* Warnings & Safety
* General Information & Procedures
* Factory / Stock Setup
* Rebuilding / Removing and Installation

* Upgrade / Improvement Considerations
* Upgrading
* Customizing / Alternative Setups
* Tuning / Examples

Submit corrections and additions to this information to The Olds FAQ Compiler.

Warnings & Safety

Stainless Steel Braided Lines/Hoses

If you go with braided stainless steel (SS) brake hoses, you should plan on replacing them every year. If you do not plan to do this annual replacement, then you should not install braided SS hoses on your car. That being said, I strongly urge you to read the following webpage on this subject:

This page explains a lot about braided SS brake hoses, which are really Teflon lines with a SS braid around the Teflon. The Teflon has advantages over rubber, but these brake lines are not bulletproof.

Here's some quotes from the above mentioned webpage:

"Here's the thing, though: Since stainless-steel lines don't bulge as they age, and since the inner Teflon lining is hidden behind the braid, there's no easy way to inspect the lines for warning signs of imminent failure."

"This is no big deal on a race car, since the lines are (or should be) replaced at least once a season. On a street car, where most people are likely to let YEARS go by without even looking at their lines, it can be an issue."

"When steel-armored hoses were run through a test, it was found that the hoses tended to bend right at the junction between the hose and the hose-ends. After a while, the stainless-steel braid would start to tear, and the broken wires would cut into the inner Teflon liner, causing it to fail."

I have seen other postings on a different car forum where people have seen this same type of failure - over time the steel braid cut through the Teflon brake line.

So, again I urge you to read that webpage, and be fully informed before you consider whether stainless steel lines are right for your car. Brakes are no place to cut corners, so if you don't want to make the commitment that SS lines require, then you should stick with rubber, IMHO.

[ Thanks to Drew Senko for this information. ]

General Information & Procedures

ALL brake systems I have ever encountered on cars have been of the hydraulic kind. I believe some trailers have electric brakes and some heavy duty trucks and semis have air brakes. A hydraulic brake system works by generating pressure in the master brake cylinder by way of a piston which is connected to the brake pedal. This pressure travels through the brake lines to the calipers and/or drums, which causes the calipers to press the pads against the rotors or the wheel cylinder to press the shoes against the drum.

In addition, there is a boost system of some kind if the car is equipped with power brakes. The most common boost system is by using engine vacuum to pull a diaphragm that helps you push the master cylinder piston when you press the brake pedal. My BMW uses the pressure generated by the power steering pump to boost the brakes and I'm sure some cars have an electric boost system. You can check and see which booster you have by looking at the booster itself, it's the large round contraption that the master cylinder is bolted to. If there is a large vacuum hose that runs from the brake booster to the intake manifold, you have a vacuum booster (which I think is the most common kind).

Drum brakes require more fluid to operate than disks. Disk brakes do not retract from the rotor when released. They just loose pressure and friction when stopped. Drum brakes have springs to retract the shoes from the drums. These springs are required as the front brake shoe becomes self energizing with tire forward rotation. The pistons in the wheel cylinders are forced to retract into the cylinders sufficiently to assure disengagement.

The reason that rear brakes lock first is that during severe braking the vehicles weight transfers to the front wheels. As you unload the rear tires the pressure needs to be reduced to limit wheel lockup. This is cumbersome to do so the manufactures reduce rear brake pressure in all conditions. depending on the weight distribution height tire size etc, etc. 75-90% of the stopping power comes from the front brakes.

[ Thanksk to Erik Nowacki for this information. ]

Compression Nut Removal

Ah, yes, the old flare-nut-rusted-to-the-steel-line trick. Chances are, you're screwed, but here are a couple of things to try first:

The soak-it-with-penetrating oil suggested by others should be the first thing you try, but I must admit I've not had good luck with this. Again, as others have noted, do not even attempt to turn the nut without using a special flare nut wrench, as you will be guaranteed of rounding the nut. Usually, however, you'll simply start twisting the hard line.

Failing that, and not wanting to give up on saving the hardline just yet, here's a last-ditch thing to try. Unbolt the bracket holding the rubber line to the frame and remove the clip holding the line to the bracket. Pull the C-clip off of the fitting on the end of the rubber hose and you should be able to slide the bracket down onto the rubber hose. Since you'll be replacing this hose anyway, cut it somewhere in the middle and remove the bracket. Now, firmly hold the flare nut on the hard line (if all else fails, you may even want to use a vice grip pliers) and use another wrench or pliers to turn the fitting on the hose while holding the flare nut stationary.

If you manage to succeed in loosening the hose fitting, you can now attempt to break the flare nut free from the hardline. If you succeed, great, if not, you can reverse the process of holding the flare nut while turning the hose fitting. In this case you will need to remember to pull the C-clip off the fitting and slide the bracket on temporarily until you get the hose tightened on the flare nut. In addition, if this is a drum brake setup, you'll need to unbolt the wheel cylinder from the backing plate, pass the new hose through the hole in the backing plate, and screw the wheel cylinder onto the new hose before reattaching the wheel cylinder to the backing plate.

[ Thanks to Joe Padavano for this information. ]

Bleeding the Brakes

When performing brake work, if your brake system is working well before you change the brake pads (no squishy pedal) and you're careful when you take off the front calipers to keep the bleeder screw at the topmost point of the calipers at all times (turn em upside down and sometimes air will leak past the bleeder screws) you probably won't need to bleed the brakes after you're done. Pop the new caliper and new pads back in place, pump the brake pedal a couple of times to take up the clearance you made when you pushed the caliper piston in far enough to fit the new pads, make sure you have a firm pedal, then take the car off the ramps or jackstands. I've done this many times during my problematic 12" brake rotor swap, with no problems.

On the other hand if you're feeling industrious it never hurts to bleed the brakes. The easy way is to just crack each bleeder screw slightly and let gravity do the work. Fluid, and any air bubbles, will dribble slowly out of the bleeder. It will take 5-10 minutes to bleed each caliper as the fluid flow is quite slow. Make sure to remove the master cylinder reservoir cover plate, and keep the master cylinder reservoir topped up as the fluid bubbles slowly out of the bleeder screws, if you let the master cylinder reservoir get dry you'll suck air into the system from the top and then you have to bench bleed the master cylinder, which is a pain and requires disconnecting the brake lines to the master cylinder.

If you have a helper, the usual "pump brake pedal slowly three times, hold brake pedal to floor, crack bleeder screw, let bubbles and fluid spurt out, close bleeder screw, let brake pedal up, repeat until no more air, repeat at each bleeder screw" procedure works very well.

Whatever method you use, it's a good idea to slip a length of rubber vacuum tubing over the head of the bleeder screw, and immerse the free end in a small mason jar or similar container with an inch of brake fluid in the bottom. This will reduce the chances of sucking air back into the system, and also minimize brake fluid spillage on the ground. A very small amount of brake fluid can contaminate a very large amount of ground water, so it pays to be careful here.

[ Thanks to John Carri for this information. ]

Bleeding Master Cylinder

The easiest way I know to do this is actually to mount the master cylinder in the car, rather than in a vice, but leave the brake lines disconnected. Then connect up the plastic adapters, run short lengths of rubber vacuum tubing from them back into the master cylinder reservoirs, and bleed away using the brake pedal, from inside the car. Not only does this eliminate the hassles of trying to push in the plunger with the tip of a slippery phillips screwdriver covered in brake-fluid or whatever, but also there is less chance of air creeping back into the master cylinder while you transport it from the vice to the car and mount it up. If it's already in the car, it only takes a few seconds to remove the plastic adaptors and hook up the brake lines, and there is less likelihood of fluid dribbling out and air going in to replace it.

Ideally you have a friend watch for the bubbles while you pump away (slowly!) at the gas pedal, but you can do it singlehanded by just plain overkill - pump till you're sure there can't be any bubbles left!

[ Thanks to John Carri for this information. ]

Factory / Stock Setup

1967-1968 Disc Brakes 4 Piston Calipers

Although the calipers off of other GM applications may appear to be the same as the Cutlass/4-4-2's, they are often not interchangeable. The calipers used on the Cutlass/4-4-2 feature 2 1/16" pistons. Whereas the Nova/Camaro/Firebird use 1 7/8" pistons. The Corvette calipers while also similar in appearance also use 1 7/8" pistons. The only (OEM) four piston calipers that will directly interchange with the Cutlass/4-4-2 are used on the other 1967-1968 A bodies (i.e. Chevelle, Skylark/GS, LeMans/GTO).

As for the calipers themselves, one big advantage of the 1969-up calipers over the 1967-68 units is that the later calipers use a piston seal fixed in the bore and a chrome plated piston which slides in this seal. The chrome prevents the piston from rusting, and since the sliding surface is between the piston and the seal, pitting in the caliper bore itself in relatively unimportant. Contrast this with the earlier (four-piston) calipers, where the seals are fixed to the pistons (sort of like the engine's piston rings) and thus the sliding contact is between the seal and the caliper bores. In this case, even minor pitting in the bores has an obviously detrimental effect on sealing. That's the reason why you see so many ads for companies that put steel sleeves in these calipers.

[ Thanks to Joe Padavano for this information. ]

1970 - 1972 Master Cylinders

There was some discussion earlier regarding the differences between the 1970-1972 master cylinders. Hopefully the following info will help:

1970 Power disc. All models (1st design. Dual bail) 1.125" bore.
1970 Power disc. All models (2nd design. Single bail) 1.125" bore.
1970 Manual disc (including W-30) dual bail. 1" bore.
1970-1972 Power or manual drums. Single bail. 1" bore.
1971-1972 Power disc. (incl. W-30). 1.125" bore. (Same as '70 2nd type).
1971-1972 Manual disc (W-30). Dual bail. 1" bore.

[ Thanks to BAP ( for this information. ]


The drum brake spindles have three mounting bolts, two at the bottom to which the steering arm attaches and one at the top for the backing plate. Typically aftermarket disc brake conversion kits will include a caliper bracket which picks up at least two of these three bolts. Note that even the factory 1967-72 disc brake spindles used a separate bolt-on caliper bracket, unlike later cars where the caliper mounting features are forged integrally into the spindle.

[ Thanks to Joe Padavano for this information. ]

Rebuilding / Removing and Installation

Master Cylinder Replacement

First, to test your current master cylinder, check the brake fluid level, look at it to see if there are any visible leaks, press the brake pedal hard and see if the pedal sinks toward the floor under pressure. If it sinks or if you have visible leaks, your master cylinder is bad. It could be bad even without these symptoms, but these are the most comon ones.

Replacing the master cylinder is probably one of the easiest jobs you can do on a car. Start by removing the actuating rod from the brake pedal. If you look under the dash, you can see where this rod attaches near the top of the pedal. It is probably attached with some kind of retainin clip that you have to remove first.

Then place some kind of protective cloth under the brake cylinder, there will be some leakage. Remove the brake lines (I recommend a tubing wrench if you have one), then unbolt the master brake cylinder from the booster (usually 2 bolts).

Before you install the new master cylinder, you must bench bleed it. When you buy a rebuilt or new master cylinder, you should get a bench bleeder kit with it. Essentially it is a couple of hoses that you run from the brake line attachment points back into the reservoir and pump the piston untill there are no more air bubbles.

The installation is the reverse of disassembly. Mount the cylinder on the booster, attach the brake lines and attach the actuating rod to the pedal.

Finally, it is time to bleed the brakes. Start at the wheel that is furthest away from the brake cylinder and work your way toward the master brake cylinder. Make sure the reservoir never runs dry. Since you will be bleeding each wheel, why not push enough fluid through the lines to bleed them at this time? A quart or two should do the trick.

I just did this on my Vista Cruiser. Total cost was $45 for a rebuilt cylinder and $2.50 for some brake fluid. Total time was less than 1 hour, including bleeding the brakes.

[ Thanks to Erik Nowacki for this information. ]

Parking Brake Adjustment

Having the parking brake on while backing up or going forward will make your rear brakes engage. If you were able to move the car with the brake fully on, the cable is probably out of adjustment. One side could also have been dragging more than the other which would help explain the "cup" of brake dust you found. You would probobly do well to re-adjust your parking brake cable. With the parking brake on and backing up, it is possible that the adjuster assembly expanded too far on one side (because the shoes were already expanded outwards against the drum by the parking brake cable) causing your brakes to drag. A parking brake cable left on a couple of notches may also do this (cause a slight dragging). I emphasize that you should not be able to move your car in reverse if the parking brake cable is adjusted properly. NOPE, I haven't had to adjust the cable on any of my cars yet, so consult the shop manual for that procedure. However, I have done the rear brakes and hence the adjuster assembly several times, so read on for some "care and feeding" tips.

The brakes do get adjusted during braking when the car backs up. You will notice a "star wheel" between the bottom of the two rear shoes. The star wheel is turned by a plate which mates with the flanges on the star wheel, but only while braking in reverse. Note the design and play with it to get the idea. It's usually handy to use a screwdriver to close or shorten the adjuster assembly. Wearing gloves you can adjust it with your fingers quite a bit.

When I take the rear brakes apart, I ALWAYS disassemble, clean, and lubricate the adjuster assembly. An old toothbrush and some "parts cleaner gasoline" work great! The gas has evaported long before you put the parts back in, so there is no risk of fire, etc. Paint thinner work great as well, and has less odor and is less toxic. The short end of the adjuster assembly has a cap which slides off; clean this and then lubricate with some lithium/white grease; do the same with the threaded end on the long side (un-thread, clean, & lubricate the threads along its entire length). If rusty, feel free to use some steel wool or wire brush to clean the threads well. The LH & RH sides are threaded the opposite of each other, so don't get them mixed up. Once the entire assembly moves freely, put it back together; if the assembly does not move freely after your best efforts at cleaning, just buy new ones. They are well-worth it and less than $10.00 each. I believe I also got all new shoe springs and retainer springs and pins as well in this kit.

Another good place to lubricate is the contact points of the backing plate -- where the brake shoe sides contact the plate; just don't get any grease on the face of the shoes. This helps since the shoe assembly does move back and forth on the backing plate under the forces of braking.

Proper re-assembly is critical to adjuster effectiveness. Expand the adjuster until you can barely place the drums back on over the shoes BY HAND. You will hear a metallic screech as the pads slide over the drums as you force/push them on. Move the drum around on the shoes; it should not rattle. If it does rattle, take the drum back off and expand the adjuster some more. This ensures you have good shoe contact with the drums. Once the drums are "sufficiently tight" and you are back on the road, the final step is to back up several times in reverse to about 20MPH. Step firmly on the brakes, just keeping them from locking up. This gives you maximum rear adjustment. You cannot over-tighten your shoes this way.

The adjuster tab will simply pop over the star wheel when fully adjusted. Do this periodically to make sure your shoes maintain proper contact with your drums and wear evenly.

[ Thanks to Bruce Brumm for this information. ]

Upgrade / Improvement Considerations

Disc Brakes

For front disc brakes, just to throw a few ideas out for you, you have two options. First is to source a factory 68-72 disc brake setup. The other is to convert over to the F/B/X/1973-77 A-body spindle.

The advantage of the factory discs is that it's a simple bolt in using all factory parts. The downside is that they are getting hard to find, and when you do find them, they usually need a fair amount of new parts (rotors, calipers, hoses, etc.). The downside of the later spindle is that it takes a little more effort on your part to make it work but can usually be accomplished for less than the factory setup. The reason is that the donor cars are so plentiful that you can usually find a car that has just been pulled into the yarde that has a recent brake job where all the parts are serviceable. This is aside from the handling benefits that are the usual reason for the spindle conversion.

1964 - 1972 A-Body Front Drums to Discs

Front Disc Brakes
Converting from drums to discs, the results are great. The car will have much greater braking than those four wheel drums. Plus if the brakes get really wet for some reason, the car won't pull which ever way it wants to. Make sure to get all the parts, brake lines, spindles, proportioning block. If you want to have manual disc brakes use a master cylinder for a W-30 stick or W-31. You can still find them at you auto parts store.

While the factory disc brakes are light years better than the drums, they are still significantly worse than those available on just about any new econobox. You may want to investigate upgrading even further to the larger F-body brakes instead. This obviously takes you even further from original, so you must consider if this will be a driver or a show car.

Obviously, you will need more than just the spindles. In addition to the discs, calipers, backing plates, and master cylinder, the frame brackets to which the hoses attach, and the proportioning valve. From the donor car you will need to take everything from the spindle to the dust cap, along with a combination valve, which is the valve that distributes the brake fluid via the brake lines to both front wheels, rear wheels and incorporates the brake warning light switch. Older cars use seperate proportioning and distribution valves.

You will also need a disc brake master cylinder along with possibly the brake lines that go from the master to the combination (or proportioning and distribution) valve(s). Remember to get the disc brake hose brackets that bolt to the frame and connect the flexible brake hoses to the hard steel brake lines. And of course, purchase new disc brake hoses.

One other thing to note: The disc brake master cylinder flare nut fittings use different size threads than the drum unit. Unfortunately, these are not standard for the tubing size used, so if you bend up new lines from the auto parts store pre-flared tubing, the fittings will be wrong. You can buy adapters (you may have to search a while to find them), use the lines from the donor car, or bend new lines and reuse the fittings only from the donor car.

Avoid 1967 to 1968 four piston caliper units. The single-piston calipers from '69-'72 are preferred, and a setup from a '71 or '72 is even more preferrable, as the separate metering valve and proportioning valve are combined into one combination valve. You should use the master cylinder and combination valve from the disc/drum setup, though you'll still have brakes if you don't.

The only parts you can't buy over the counter at your local parts store are the spindles, combination valve, and very-importantly, the frame mounting brackets for the front brake lines, so if you have to get a setup, make sure you at least get those parts. If everything else is in good or rebuildable condition, however, get them as well.

If your car has a single circuit system, invest in a tubing bender and make the system into a dual-circuit system (your stock master cylinder would only have one resevoir for the entire braking system; should one part fail, it all fails).

To convert an A body (Cutlass) from drums to disc brakes, there are a number of options (some apply to full size as well):

  1. 67-68 A-body four-piston caliper discs. This is a bolt-on, and is correct for your car (if you care). Unfortunately, these pieces are quite rare (read: expensive) and frankly, not the best design.

  2. 69-72 A-body single-piston caliper discs. This is also a bolt-on, but uses the much more common (and some, like myself, will argue better) sliding caliper design. Both Options 1 and 2 bolt on from the steering knuckles outboard.

  3. Second generation (70-81) F-body discs. This setup uses the spindles from the Camaro/Firebird family, which were available with bigger brakes (11", I think) than the A-body cars. The parts are quite common, but unfortunately, require an adapter kit (and preferably, a new upper control arm) to fit properly. The advantage (aside from the larger brakes) is an improvement in handling as well. Global West Alignment (in Ontario Ca. (714)923-6180) sells the kit for adapting these brakes.

  4. Aftermarket brake kits. Several companies make extreme (read: very expensive) high-performance disc brake kits for A-body cars. The most well known is Baer (yes, that is the correct spelling), which makes a 13" kit. Engineered Components Inc. (ECI) also markets a kit which allows the use of Corvette brake components on both the front and the back of A-body cars.
[ Thanks to Mike Bloomer, Chris Smetana, Jim Chermack, Joe Padavano, Bob Barry for this information ]

Consider that most kits, even those containing factory upgrade components, will cost just about the same if you sourced/pulled/located the components yourself.

Using parts yard parts for the drum to disk conversion, and having all the parts removed by the yard, cost about $75. Resurfaced the rotors (approx. $15), bought new pads (approx. $15), new hoses (approx. $40), and a new master cylinder (approx. $40) for a total of $185.

[ Thanks to John Monnin, Bill Culp for this information. ]

Difficulty Factor
The work isn't hard and can be done with ordinary tools. You would need some of these parts in restoring your car anyway (master cylinder, brake shoes, hoses, turn drums). The cost isn't out of line at all.

[ Thanks to Bill Culp for this information ]

Optional Suspension Upgrade
The B/F/X/73-77 A-body disk-brake upgrade/negative roll conversion spindle swaps on the 64-72 A-body change the front track width of the car. The front track will widen enough that some tires no longer fit inside the wheelwell with adequate clearance. See later sections on this page for details.

[ Thanks to John Carri for this information. ]
Rear Drum Factor
Disc brakes stop much better than drums, but for those of you with four wheel orginal drums, retain your rear drums which have much surface area, reduced in later years because of increased stopping power of front discs.
[ Thanks to for this information ]

Rear Disc Brakes:

I've done a lot of research on front and rear disc conversions lately as I work on my 1966 442. There are a lot of options, ranging from somewhat expensive to very expensive. I'll try to briefly outline what I've found. I should note that the original post (Matt's, I think) asked about discs for a Type-C 12-bolt. These kits are much more common than those for the Type O, obviously.

There are a number of weld-on options available. I've been concentrating mainly on the bolt-on options, however. I've also concentrated on rear disc kits with emergency brake options, as I plan to run this on the street. There are many racing-only kits without the e-brake (Mark Williams and Wilwood, to name two) which use bolt-on brackets and fixed four-piston aftermarket calipers. These kits, in addition, use aftermarket rotors which typically use an aluminum hat section and a steel rotor. The goal for most of these kits is reduced weight for racing in addition to increased stopping power.

In the street brake area, one of the lowest-cost systems I've seen is from ECI (Engineered Components, Inc). This system uses Seville/Eldo rear calipers with integral parking brake and includes a bolt-on bracket. The rotor appears to be the second generation F-body rear rotor, which is something like 10.75" in diameter. I believe some minor machining of the axle shaft pilot is required to clear the rotor, which is 1.1" thick.

ECI also markets a rear disc kit using the rotors and calipers from an 1984-87 Vette. These are 12" rotors, 0.81" thick, and aluminum calipers, but there is a problem in adapting this kit unless you also use Vette front calipers. It seems that the newer Vettes require a higher pressure due to the size of the caliper pistons, requiring a unique master cylinder. It isn't possible to mix Vette rears with A-body fronts. ECI used to market a front disc kit for the A-body using the Vette calipers, but discontinued it due to lack of interest. This rear kit is mainly for street rodders using Vette front brakes and a 12 bolt rear.

Wilwood makes a street rear disc kit for the 12-bolt. It includes 12" aftermarket rotors (either 0.81 or 1.25" thick, I don't remember) and fixed four piston aftermarket calipers. They use a separate mechanical caliper as the e-brake. Bolt-on brackets are included. They also market a matching front kit which include a machined aluminum hub and the same calipers and rotors.

Top of the line is Baer Racing. You've seen their Baer Claw systems in numerous magazine articles. Front and rear kits are available using 12", 13", and 13.5" rotors in thicknesses from 0.81 to 1.25". Their least expensive kits are based on the 1984-87 Vette rotors and calipers (again, you must match fronts and backs). Mid-range uses the 1988-96 Vette designs (13" rotors with 1.1" thickness, same calipers), while the high end uses 1.25" thick rotors and aftermarket Alcon fixed four-piston calipers. A complete four-wheel conversion kit for an A-body (note that this is a complete bolt-on setup with master cylinder, braided lines, pads, front spindles assembled and ready to bolt on) starts at $2200 or so. Top of the line kits exceed $5000.

Finally, it is possible to adapt the second generation F-body rear discs to a 12-bolt, which is basically what ECI did. You can use the OEM-style caliper brackets, though I seem to recall that they needed to be redrilled for the axle end bolt pattern.

Note that someone on the list (Scott Wheeler, perhaps) indicated that the Type-O axle end bolt pattern matches the Type-C and that those kits should fit the Olds axles as well. If you are running a Type-C with aftermarket C-clip eliminator kits, the brake kits either may not fit or may need to be modified.

At this point, a little editorial comment. I plan for my 1966 to be a driver and I want to be able to get parts for it if I take it on a trip and have a problem. As a result, I'll probably shy away from kits that use aftermarket rotors and calipers. In addition, since this car will be driven in some inclement weather (rain, for example), I'm concerned about the effects of galvanic corrosion where these aftermarket kits have aluminum parts in contact with steel (say, the aluminum hats on the steel rotors). As a result, I've committed to using the B-body 12" brakes on the front, with OEM-style calipers, and I'm currently struggling with the backs. I really want 12" rotors on the back, but I want to use OEM parts, including the Seville/Eldo calipers. One thing I'm investigating is the use of the 12" diameter by 1.1" thick 1988 Vette rotors, which should have the correct 5x4 3/4 lug bolt pattern. The potential problems are the rotor offset (distance from the centerline of the rotor to the axle flange) and the fact that no caliper brackets exist for this combo. I've already assumed I'll need to use the F-body brackets and modify them.

For rear disc brakes on a budget, use the late 70's/early 80's Trans Am rear disc set-ups. Most of the parts are available, but the cost from GM was more than the $625 that the Wilwood kit costs from Summit. At least the Wilwood kit gives you 12 3/16" rotors and aluminum 4-piston calipers. VERY nice quality. I was surprised at the vast quantity of disclaimers on every component of the Wilwood kit.

One factor to consider is to measure the run-out on the rear axle shaft flange. My friend had to have the axle flanges trued at a machine shop to eliminate rear disc wobble and pedal pulsation. This was a cheap operation. He even used his stock master cylinder, drilling a new hole in the brake pedal rod to mount the push rod at an angle that provided good pedal action and favorable pedal height. As I perform this operation on my car next month, I'll let any interested parties know how it went. Best of all, only the truly observent will ever notice the non-stock rotors peaking through the rear wheels.

The following fabricated parking brake setup can be used. I drilled a hole in the brake pedal arm that was approximately halfway between the two existing holes to give a better feeling pedal geometry. All in all, I heartily endorse Wilwood's products on the basis of quality and design of components.

[ Thanks to Scott Mullen, Joe Padavano for this information. ]



This is not an all inclusive list of aftermarket suppliers, just examples of what has been discussed on the Olds Mail List.

Name E-mail Website Notes
Global West (909) 349-2090 - Sold directly
HO Enterprises (909) 608-0022 - Sold directly
Hotchkis Performance (562) 907-7757
Malibu Performance (818)222-6725
Wilwood (562) 907-7757 - Sold directly

1964 - 1972 A-Body Front Drums to Discs

You'll need:
  1. Spindles
  2. Larger piston master cylinder
  3. Proportioning valve for the rear brakes and valve for the front brakes.
  4. New hoses for the front calipers.
  5. Frame brackets that hold the inboard end of the hoses to the calipers. These are different for disc brake hoses
  6. Flare nuts for the lines to the front wheels. GM used some non-standard size flare nuts to ensure that the lines could not be cross connected on the assembly line. Unfortunately, these flare nuts are not readily available. Your options are 1) grab the lines (if in good condition) from the donor car, 2) buy repro lines, 3) get the flare nuts from the donor car and bend/flare your own lines, or 4) use adapters (ugly, but it works).
  7. Wheels to clear disc brakes. Prior to 1971-or-so, GM used different wheels on drum cars than on disc cars. The 14" drum wheels will not clear the calipers on the disc setup. All SSII/SSIII rims will clear, however the SSI rims come in two flavors, the 1970-earlier (which do not clear) and the 1971 (which do).
  8. The power booster is a little trickier, as you must get a power booster from a car with a dual-circuit braking system (1967-up). I know from experience that the 1967 booster will work on a 1964-66 car, but I don't know personally if a 1968-up booster is a bolt-in. The problem with all of these is that the booster is larger in diameter than the 1966 booster, which may force you to get the factory "notched" valve covers for clearance on your big block. Alternatively there are a number of small diameter aftermarket boosters available as well.

Master cylinder/power booster
The early-style small diameter power booster will not work with the dual-reservoir master cylinder due to the length of the pushrod (it's longer on the early boosters). You can disassemble your early booster and rebuild it with a shortened pushrod, however the length of the pushrod is critical for proper brake functioning, so unless you can get the exact measurement and have access to a machine shop, this is probably not a good choice. The large diameter booster from a 1967 works with the dual-reservoir M/C, will bolt up to all 1964-67 A-bodies, and it will clear the valve covers on a 330 or other small block Olds. I can't say for sure if it will clear a big block (the "notched" covers may be required, or it may not fit at all - I just don't have any experience here). You can also go with the aftermarket small diameter boosters (a la Mondello and others), but be aware that they are not necessarily a direct bolt-in.

The following spindle part numbers are listed in the dealer parts book for disc and drum brake applications for A bodies:

Application Part Number
1966 (and presumably earlier) 385091
67-69 Except Disc Brakes 396876
67-69 Disc Brakes 3894475
68-69 Canadian (?!??) 1383958
'69 A Body disc brake metering valve 3905525

Note that my parts book only covers 66-69, however I assume that 64-66 are the same, as are 67-72. I was surprised that there was a different listing for disc vs. non-disc. I was even more surprised that there was a different listing for Canadian-built cars, which did not specify disc or non-disc. I infer from this that either there is no functional difference between the spindles, or there were no disc brake cars built in Canada (my first 68 442 was Canadian-built and it originally had drums). Note also that the four-piston (67-68) and single piston (69-up) calipers both use the same knuckle.

I did a little more research in the parts book, and discovered that the bolts which hold the backing plate/caliper bracket on the knuckle for both disc and drum applications for 67-up are the same, implying that while the part numbers are different, the knuckles should be functionally interchangeable. Unfortunately, all of my drum brake hardware is long gone, so I can't easily compare the two.

1966 and earlier cars used a smaller diameter bolt to hold the steering arm to the knuckle (one of these bolts also holds the lower end of the caliper bracket). This means that when adding discs to the early cars, one must swap the complete knuckle.

You are right in that the listing of P/N's are different, but the 70 Cutlass I changed over to disc had the same part number stamped on the back of the spindle assembly for both spindles (disc and non-disc). Both sides were the same way. I just reused the old spindles and bolted up the disc brake parts. Strange, but it fit like it was supposed to.

The top anchor bolt hole is recessed on the disc brake spindle.

Brake line flare nuts
GM, in an attempt to prevent the incorrect connection of brake lines on the assembly line, tried to make every different connection a unique thread size. As a result, GM used some non-standard flare nut fittings on the brake lines going to the M/C and proportioning valve. When I say non-standard, the male thread on the nut is not necessarily the same one that you'd get if you went to an auto parts store and bought a flare nut for that size tube. The result is that when you get the disc setup and proportioning valve from the donor car, be sure to get all the mating flare nuts. You may need to reuse some of them. In a pinch, you can also get adapters from most well-stocked auto parts stores, but this is a less than sanitary solution, due to the added chance of leakage.

Proportioning valve
GM used two different valve configurations, the integral and the separate. The separate design was used from 1967-70, and usually takes the form of a valve mounted below the master cylinder and plumbed in series with the rear brake line between the M/C and the brass distribution block. Typically cars using this separate proportioning valve used the same distribution block as the drum cars. Starting in 1971, the proportioning valve was combined with the distribution block (and the brake warning light switch, which was also located in the drum brake distribution block) into a single housing which mounted to the frame near the starter. As has been discussed here before, there are a number of different proportioning valves, each calilbrated for a specific application (2 dr, 4 dr, wagon) due to the differences in weight distribution. Unless you can get one from a donor car of the same configuration as yours, you may find it easier to go with an aftermarket adjustable proportioning valve. Note that you will need to do some experimentation on valve adjustment if you choose this route; this testing must be done in a safe area (empty parking lot, for example). If you go the adjustable route, do not use a factory proportioning valve. Instead, use the drum brake distribution block and plumb the adjustable proportioning valve in series in the line to the rear brakes; it can be located on either side of the distribution block.

Distribution block location
If you plan to run headers at any time, locate the distribution block somewhere other than the stock location on the frame rail. If the car is an automatic, I've found the top of the frame rail below the M/C to be a good location.

Parts Cars

The following can provide disc brake setups for swapping to A bodies:

67-74 Nova's and clones
68-72 Buick Specials
68-72 Chevelle
69-72 Grand Prix
67-72 Tempest

Other Links

A complete writeup on the B,C,F,X-body spindle swap conversion is at: .

The Chevelle Online Interchange Manual has some good information. Since the Chevelle is an A-body, much of the information should apply to Cutlasses.

A list of the parts required for the 12-inch brake conversion under the chassis section. It's at:

[ Thanks to Doug Kitchener, Greg Pruett, Bob Barry, Mike Rothe, Joe Padavano, Doug Kitchener, Stephen Hoover, Walter, Scott Mullen for this information ]

1965 - 1970 B, C-Body (full size) Front Drums to Discs

I know a good deal about the swap to disc brakes in big cars. Here are the main points:

1965 to 1970 full size cars (88s, 98s) ran the speedometer off the driver's side spindle. Rear gear independent!

You might want to put in the master cylinder from a Chevy Tahoe or Suburban. These have the plastic reservoirs that you can see the brake fluid in and are setup for a vertical, not slanted, firewall. Also these are all dual circuit masters cylinders.

On the big cars from 67-70, the drum and disc spindles are definitely different. There is a horizontal interference between the spindle and the rotor a little way (moving from center to outer diameter) into the machined portion of the rotor. You could potentially have it machined off, but why not just get the right thing. Have it magnafluxed to check for cracks though before using, remember, it had a full life before you put it in your car.

[ Thanks to Chris Fair for this information ]

4 Piston Calipers

4-piston unit do offer the advantage of pistons clamping on both sides of the rotor, but our stock car that operates on a fairly demanding asphalt oval (brakewise) will do just fine on a set of their floating single-piston units with cooling ducts from the front of the car attached to the spindle.

While technically not correct for a 1967 or 1968, the later single piston calipers are better, and are more plentiful. The modern single piston design was introduced in 1969 and carried forward from there.

One other consideration is that the four caliper pads are murderously hard to find, and expensive. Four piston calipers were offered in 1967 and 1968. Not only are parts expensive, but the calipers are fixed to the spindle, not floating, and thus any side-to-side wobble in the rotor causes the pistons to be knocked back into the caliper, greatly increasing pedal travel; not the best design.

In addition, the early units use the caliper cylinder wall as the sealing surface (rubber seal ring is on the pistons), which makes them susceptible to rust and often requires the calipers to be sleeved. The later units actually have the seal ring in the caliper bore and use the piston surface as the sliding surface. The piston is then chromed, which prevents (or at least delays) any rust effects. In addition, a replacement piston is a lot cheaper than four sleeves for the early caliper.

The spindels from 1968 to 1970 are the same, but the calipers are a little different. So buy new calipers and the problem is solved.

[ Thanks to Ken Snyder, Joe Padavano for this information. ]

Brake Fluid

Convert from DOT 3 to DOT 5 in conjunction with a complete brake system rebuild. Start by removing all lines from the calipers or brake cylinders. Rebuilding is a good time to perform the conversion since you can rebuild and clean the calipers and/or cylinders completely, which allows you to remove all DOT 3 fluid. If you are rebuilding, make sure none of your seals are silicone rubber. Most brake components are EPDM, but some can be silicone rubber, and DOT 5 (silicone) will eat silicone seals!

NEVER FLUSH THE SYSTEM BY PUMPING DOT 5 (silicone) OVER DOT 3. Does not work and it's expensive too!!! Silicone brake fluid is expensive. You will uses more than one quart, but less than two quarts of DOT 5. Prices vary, but you will spend $20-$50-70 for fluid alone in a typical change over.

Pump de-natured alcohol into all lines and use compressed air to clean them out. Master cylinder should be removed and cleaned with alcohol using a bench bleed method. With every thing clean and dry, reassemble, fill master cylinder with DOT5, and begin the bleeding process. DO NOT REUSE the DOT5 that is bleeding out. Pour only clean DOT5 into the master cylinder. Cloudy fluid is a sign you missed some DOT3 (this is usually why the brakes are spongey).

A listee reports that 99% of the people that he has converted to DOT 5 (All Corvettes, racing and street applications), do not notice any difference in the "FEEL". Silicone has a high viscosity index and therefore maintains the same viscosity over a broad temperature range. Boiling point is important but not the biggest concern. When temperatures get high, regular brake fluid gets thin and the brakes fade or pressure drops.

[ Thanks to for this information ]

Brake Hose Brackets

There are some subtle differences in the 1970 and 1972 disc-brake brake hose brackets (another essential element in a disc-brake conversion).

The hole in these brackets appears, at first glance, to be a simple hex-shaped hole. On my '70's original brackets, however, two points of this hex are kind of rounded, presumably so that the hole in the other end of the brake hose is properly positioned in relation to the caliper when the hose is installed in this bracket (with a simple hex, 2 out of 3 ways you could install it would be wrong). On the brackets from a 1972 Vista, however, only one of the points on the bracket is rounded, so the hose can only be installed one way. It appears that the '70 hoses would fit in the '72 brackets, but not vice-versa. The easiest solution to use the '72-type hoses in the '70-type brackets would be to grind off the one offending point on the hex, if you need to use that combination.

[ Thanks to Bob Barry for this information ]

Brake Linings

Soft linings (pads and shoes) don't necessaryily provide more pedal feel with manual brakes. Using Wagner metallic linings, and have had no problems (well, other than the constant buildup of black brake dust on the SSIIs).

[ Thanks to Joe Padavano for this information ]

Combination Valves, Metering Valves, and Proportioning Valves

The proportioning valve is application specific which takes the following into account: 1) whether drum/drum, disc/drum, or disc/disc 2) front/rear weight distribution of the vehicle and 3) the maximum braking force at each end of the vehicle (as in disc diameter, drum width/diameter).

The small cylinder located near the master cylinder (about the size of a 35mm film container) is the external proportioning valve. GM used this configuration through 1970 on disc brake cars in combination with a normal drum brake style distribution block bolted to the frame.

Starting in (I thought) 1971 GM went to a combination valve that incorporated the proportioning valve into the distribution block, eliminating the exteranal valve and saving dollars and part count in assembly. The two are equivalent in function, however your car must have either one or the other. It's possible that GM may have switched to the combination valve part way through the 1970 model year (is your car a late build date, for example), or your car may have been converted to discs at some point in the past using 71-up parts. Look at the distribution block on the frame of your car, below the master cylinder. This is the block that the two lines out of the master cylinder go into. If the block is a rectangular brass machined part, this is the distribution block without the proportioning valve. If it is a rounded cast iron part, it is the combination valve.

What you are referring to is a Brake Metering Valve. They are used on disc brake applications. Its purpose is to prevent the front brakes from locking before the rear shoes have a chance to activate. It functions by delaying fluid pressure to the front brakes until there is approx. 75 lbs of pressure in the system. Since the rear cylinders require more more fluid travel to push the shoes out against the drums than the discs do (as well as overcome the return spring pressure), the valve will in effect balance and equalize the pressure applied to all four brakes. The metering valves were remotely mounted to the master cylinder on all 1967-1970 disc applications. In 1971, the metering valve was combined with the distribution block. And consequently renamed a combination valve. When bleeding the front calipers on a 67-70 system, don't forget to depress the plunger on the metering valve. This is a little rubber boot covering a pin that should be held in when you are bleeding the brakes. This pin is part of the metering piston.

I'm intrigued by the statement that these metering valves were only used until 1970. As far as I know, all cars with a disc/drum brake combination use both a metering valve and a proportioning valve; the metering valve prevents brake fluid going to the disc brakes until enough line pressure has built up to overcome the springs in the drum brakes and take up the clearances between the brake shoes and drums, and the proportioning valve controls the ratio of braking force coming from front and rear wheels to prevent one locking up long before the other.

The reason for the metering valve is that without it the front disc brakes would come on at even the slightest touch of the brake pedal, while the rear drum brakes would not even move; this way the front brakes would do all the work in light braking, and wear out much faster than the rears.

The disc brake proportioning valve is definitely different than for drums. However, don't confuse that with the frame-mounted distribution block, which simply splits the two lines coming in from the master cylinder into three lines going out (one for the rear axle and one for each front wheel). This distribution block also contains the differential pressure switch which activates the BRAKE warning light on the dash if you loose pressure in one side of the system. This is the brass (usually discolored) block which bolts to the frame and which must always be moved to install headers.

The proportioning valve for A-body discs comes in two flavors. There was a separate unit which was plumbed into the line going to the rear brakes. It is about 1½ inches in diameter and about two inches long and is usually mounted below the master cylinder (the valve has a bracket which is held with one of the fasteners which holds the master cylinder to the power booster.

I seem to recall that there is another design which incorporated the proportioning valve into the distirbution block. In that design the dist. block is cast iron, not brass, and is more rounded than the square-cut brass unit. This design is mounted to the frame.

I put in the hydraulic splitter from a 1971 big car with the electrical low pressure switch to warn of loss of fluid; some peace of mind there. Wired it to the brake light for logic's sake.

Currently, I have a Direct Connection (Mopar) dial-adjustable brake proportioning valve installed in-line in my rear brake line. I installed this by cutting the main line running to the rear of the car where it runs in the frame, about even to the area where your headlight switch is. I coupled a line to the master cylinder side of the line, and ran it up through a grommeted hole in the floor pan and to the valve, which is mounted to the underside of the dash, directly below the headlight switch. I then ran another line from the valve and down through a grommeted hole, coupling it to the rear axle side of the main line.

Now I have easily accessible control for rear brake line pressure. I can thus increase or decrease pressure to the rear brakes as road conditions or brake heating conditions warrant. Prior to installing this valve, premature rear brake lock-up (i.e. rear brakes locking up before the fronts, instead of all four tires locking at the same time, which is the ideal situation), especially in wet weather, was a dangerous condition. Also, due to the uneven heating/cooling characteristics of the 12" front disc/semi-metallic shoes with rear drums set-up currently on my car, extended vigorous driving can result in a need for rapid adjustment.

Around 1971 the separete metering valve and proportioning valve were combined into one combination valve.

[ Thanks to Joe Padavano, Scott Mullen, Bob Barry, John Carri, Joe Padavano, for this information ]

Eliminating Junction Block:
I eliminated the factory junction block by straight plumbing the lines and installing an adjustable proportioning valve. Adjust it until the rears lock up right before the fronts and your good to go. Jeg's list a Wilwood unit for $39.99. If you used the factory 2 piece spindle disc brakes (up to 1972) you could use an original proportioning valve from an original disc brake car, but that may be a pain to find.

I'm trying to bypass my proportion valve to the rear brakes. I would like to use a union from the line of the master to the line that feeds the rear. It seems to be a very odd ball size i have gone to several places. My lines are all stainless steel so I cant cut and flare. By the way im trying to add an adjustable proport. valve.

What you've suggested will work (just don't forget the adjustable proportioning valve), however be aware that the brake pressure warning light will no longer function properly. The switch for this light is built into the combination valve (I assume you have a 71-later car, otherwise this is not the case) and senses a differential in pressure between the front and rear brake circuits. If you bypass the valve, the switch will think that you've lost pressure in the rear brake circuit and the light will stay on. If you simply want to eliminate the light (and thus the warning function), pull the electrical connector off of the combination valve. After doing this, the light will still function to indicate that the e-brake is on, but you will obviously lose the brake pressure warning function.

As for the fittings, as you've noted, GM used unique, non-standard flare nuts on the lines to preclude the chance of misconnections on the assembly line. Find an auto parts store which is well-stocked in adapters (they're out there) and have at it.

Also, if you feel you'd like to retain the brake pressure warning function, replace your combination valve with the distribution block from a drum brake car. This block has the pressure warning switch, but no proportioning valve. Then, simply plumb the new adjustable proportioning valve into the line going to the rear brakes. This is actually how the 67-70 disc brake cars are plumbed.

[ Thanks to Mike Bloomer, Joe Padavano for this information. ]

Correct Combination Valves (1970-72):
The 2 function valve is used on manual disc brakes and all station wagons.

The 3 function valve is used on everything except manual disc brakes and all station wagons.

OAI has nothing to do with the brake system (this is why I questioned the description from Year One). After spending some time at the local Olds parts counter cross comparing the parts books and the service manuals, we determined from the GM descriptions that someone at GM must have thought OAI and W30 meant the same thing. The 3 function valve is p/n 2550-9418 and the 2 function valve is p/n 1257177.

Both have the warning switch and metering valve functions, but the 3 way adds a balance function. The balance function "operates to reduce the pressure of the rear brakes because of weight shift during high deceleration stops to improve front and rear brake balance." With that being said, either valve should function, but the proper valve would give better hard braking control.

BTW, combination valve is the correct term since the 2 function valve does not have the balance (proportioning) function.

[ Thanks to Kurt Heinrich for this information. ]

Cross Drilled Rotors

Cross-drilled rotors will crack easier and will wear pads out even quicker than non-drilled rotors. Most manufacturers will not recommend cross-drilling rotors.

[ Thanks to Ken Snyder for this information. ]

Flare Nut Fittings

Note that the threaded flare nut fittings on the brake lines going into the M/C are different sizes for drum and disc brakes, specifically to prevent installation of the wrong part on the assembly line. I have to assume that since my car currently has a disc M/C, and these lines and fittings haven't been changed, that it originally had a disc M/C.

[ Thanks to Joe Padavano for this information. ]

Four Piston to One Piston Caliper Conversion

Although there were different rotors used form the factory, all 1967-72 GM A Bodies use the same replacement rotor (.965 inch discard if memory serves). The pads on a 1968, like the calipers, differ from the 1969-72 ones.

The single piston calipers will bolt on to the 1968 car if the caliper mounting bracket is changed as well. This part bolts onto the steering knuckle - get it off of the same car as the calipers.

Second, my understanding is that the early (four piston) rotors can be used on the later (single piston) cars, but not the reverse. The reason is that the two rotors differ in the relationship of the rotor face to the spindle, however the sliding single piston caliper can accommodate this difference. The fixed four piston unit will not. Please note that this information is provided second hand from a friend who claims to have done this on Pontiacs.

[ Thanks to Brent Pinkstaff, Joe Padavano for this information. ]

Hydraboost Diesel Power Booster

In converting to a hydroboost power booster, I had to change the rod on the hydroboost unit to retrofit it to my 1975. Other than that, it's pretty much a bolt in. One problem, has anyone ever removed the push rod from a hydroboost unit? I can't seem to get it out. Any advise?

By the way, I found the hydroboost unit on a mid-eighties gasoline engined big Buick wagon. I've seen MANY of them in boneyards. Look for big GM wagons, GM diesel pickups and cars, some Caddies. I had to have a push rod fabricated but I have a good friend who own a machine shop. I also had to drill one hole in the hydroboost's bracket to mount it to my firewall. The other three holes match up fine.

Cadillac used Hydro Boost in all their disc-braked '76-'78 Eldos.

For a lumpy cam, what I did was use a booster off of a (Olds) diesel Chevy truck, which runs off the power steering pump. Not exactly the cleanest looking option, but it is quiet, and bulletproof. Some of the electric vaccum pumps can be noisy. Also gives you more clearance around the engine. When you consider that to reliably run the booster off a vacuum pump, you should also use an auxilary vacuum tank, it comes out looking a lot cleaner if you route the lines right, IMHO.

As for the vacuum pump I have seen them at the local chain stores and JC Whitney catalog. Once again, I would strongly recommend using a vacuum resevior in this setup for safety. You never know when you'll have to hit the brakes a couple times in a row (would suck to run out of vacuum, no pun intended).

[ Thanks to Mike Bloomer, Edward Binnix for this information. ]

Larger 1964-1972 A-Body Rear Drum Brakes

The easiest swap to upgrade the back brakes on a 64-72 A-body is to use the 11" drums from a 73-77 A-body. Just be sure to measure the parts in the wrecking yard, as the 73-77 cars came with both 9 1/2" and 11" drums. Get the backing plate, hardware, and drums. This is pretty much a bolt-on operation.

Decided one day to see if the brakes off of our junked `77 Ch*velle would fit the `72 Vista Cruiser since they were a much larger diameter. (10 or 11 inches, I can't remember). They bolted right up after a little filing on the baking plate. The hole in the backing plate that slides over the very end of the axle housing was too small by .01 inch or so. Just took a round chainsaw file and ran it around the hole until it was just large enough to slide over the axle tube and allow the backing plate to sit flush against the flange on the axle tube. The bolt holes in the backing plate lined up perfectly with the bolt holes in the flange. Stock parking brake cable worked fine, and the steel brake lines on the rearend that went to the brake cylinders on each side had to be re-bent a little bit to fit the wheel cylinders. Decided later to replace the steel lines since it didn't seem like a great idea to put new bends in 22 year old brake lines. The brakes work great. Better stopping power, less fade, and the parking brakes alone can drag it to a stop even in reverse.

I don't remember for sure, but I think we managed to unbolt the Chevelle backing plates without removing any of the brake shoes or hardware. Just had to unhook the brake line and parking brake cable.

If you swap in the bigger brakes you may need a different proportioning valve. You can try the proportioning valve from the vehicle donating the brakes if it has about the same front/rear weight distribution. Or you could get a new adjustable one($90). My Vista Cruiser didn't seem to need a diffeent valve, even in wet weather the rears don't lock up before the fronts. But the V-C has much better weight distribution than a coupe, in that it has an extra 700 pounds of rear weight. Since more of it's weight is positioned over the rear wheels it's more forgiving if the rear brakes grab better. I'm not sure if your coupe will be able to get away with it or not. If you swap brakes you'd better find a wet empty parking lot or some loose gravel where you can't do any damage if you lose control and do some test braking. Practice some panic stops. You can judge for youself whether you like the way the car is stopping and decide on whether to change valves. If the rears want to lock up sooner than the fronts the car will want to fishtail, which is not cool if you happen to be panic stopping.

The Vista Cruiser rear drums are, in fact, 9 x 2 1/2, as opposed to all other A-body cars, which use 9 x 2 rear drums (actually, I think the Buick Sportwagon also uses the 9 x 2 1/2 rear drums.

Here's the trick: All 1964-72 A-body cars with front drums use 9 x 2 1/2 drums on the front. These front drums can be used on the rear of the VC! I don't know if they are the same part number, but they are functionally identical. If you get the front drums off of the VC, compare them with the backs - I bet you'll find them the same. Back when I used to own a 1968 VC, I actually used junkyard drums off of the front of an early-70s Nova on the rear of my VC. No probs.

While we're on the subject of VC brakes, I've asked this before but gotten no response: Where is the extra 1/2" of brake width accounted for in the rear axle assembly? I notice that the parts book lists VC-unique rear axle housings, axle shafts, and brake backing plates, but obviously no dimensions. Is the extra width accommodated with dished backing plates on a normal width housing, or flat backing plates on a narrower housing? Or do the axle flanges stick out an extra 1/2" per side? If the width is accommodated in the backing plate, this is an easy way to gain 20% swept area on the back brakes on a 442. Anybody have any dimensions?

The Vista Cruisers have larger rear drums. I believe they are 1/4 or 1/2 inch wider than the regular (lesser?) Cuttlai. I don't know how much of the braking system you would have to swap out, but if necessary, the entire rear end should fit your car without any problems.

The VC brakes are 9"x2.5", whereas other A-bodies use 9"x2" drums. I've long wondered if these would swap out, but I don't know if the additional 1/2" is accommodated through an offset in the backing plate, a narrower axle housing, or different axle shaft spacing (I doubt the latter, as this would increase rear track by 1"). The parts book lists different part numbers for both the backing plates and the axle housings, but doesn't describe the differences. As you've noted, the entire housing _will_ swap.

Another option is to use the 11"x2" brakes from the 73-77 A-body cars. From what I understand, these will bolt up to the earlier cars.

[ Thanks to Erik Nowacki, Greg Pruett, Joe Padavano for this information. ]

Manual, No Assist, Brake Conversion

To convert from power assisted to manual brakes, you'll need a manual brake master cylinder (I believe the bore is a different diameter), the correct pushrod to connect to the brake pedal, and a rebending of the lines to the master cylinder due to it's new location. You'd also need to plug the port on the intake manifold used to feed vacuum to the power booster.

I converted to manual brakes on my 68 442, and used a manual master cylinder from a 1975 four wheel manual disc brake Corvette. The 442 stops really well.

[ Thanks to Butch Vosburgh, Joe Padavano for this information. ]

Master Cylinders

Consider upgrading to a 1980 or so plastic topped master cylinder. An advantage here is that you can see the fluid level. A problem here is that the master cylinder it is angled and the firewall is vertical, so you will need to find an angled vacuum assist; back to the boneyard.

[ Thanks to Chris Fair for this information. ]
Manual, Power Assist, Drum, Disc
Although the 1975 Olds parts book lists the 1970 3200, 3600, 4400 OAI and manual disc (part number 5471817) master cylinder as being the same for 1967-1972 drum brake applications. This is the only reference of these two being the same that I have ever seen. So, the '70 w-31 and stick w-30 cars (manual disc) did not use the same master cylinder as the drum brake cars.

And I can only conclude this is a typo. Reason number one being a drum brake cylinder and disc brake master cylinder do not and cannot interchange due to the fact that a drum brake cylinder requires check valves in both ports. Whereas a disc brake master cylinder cannot use a check valve in the front reservoir. I have an older Delco brake parts book that shows part number 174-318 for all 1970 drum brake applications and part number 174-262 for 1970 manual disc applications. The 1970 chassis manual also states a different cylinder used in drum vs disc applications.

I have personally restored two 1970 W-30 4 speed cars. Both were low mile originals. Both had the same disc brake style cylinder. Tonight I called a local customer who recently picked up a low mile 70 W-30 4 speed car (which by the way is for sale), it too has the disc style master cylinder. I rummaged through some old magazines and found several pictures of 70 manual disc cars. They all have the disc style master cylinder. Other than the 1975 parts book reference, I cannot find any evidence to believe that 1970 manual disc cylinders are the same as the drum brake cylinders. I would be interested to hear from other List members who own a 1970 with manual disc brakes. What type of master cylinder is on your car? The original style disc cylinder features a large front and a small rear reservoir. Whereas the drum style cylinder originally had equal front and rear size reservoirs.

There are difference (mainly internal) between power, manual, drum and disc brake master cylinders. Always get the correct one for your application! Parts sources list four different types of master cylinders:

Power Front disc
Manual Front disc
Power Front drum
Manual Front drum

Manual brakes master cylinders have a smaller piston and longer throw than a power master cylinder. The power master cylinders has a larger piston but shorter throw.

On all counts, I think you can say that you'd have some braking ability if you used the incorrect master cylinder, but you'd have optimal braking ability if you use the correct one for your application. So, there is a difference between power and non-power master cylinders (see next paragraphs). And, there is a BIG difference between drum and disc master cylinders!!

Drum brake master cylinders differ from disc master cylinders in at least ONE, and a very important way. Drum MC's have a check valve on the FRONT reservoir going to the drums to ensure that like the rear, a residual pressure is maintained by the fluid on the wheel cylinder, reducing the pressure build-up time to the brakes (read faster-acting).

The reason for the check valve is to maintain about 7 psi in the brake system to keep the cup seals in the wheel cylinders sealed. They require a small amount of pressure to maintain contact with the cylinder wall of the wheel cylinders. You should not use a drum MC for disc brakes, or vice versa.

Without the check valve, residual pressure is not high enough to keep drum brakes engaged. Disc brakes do not have this check valve in the front, for if there were any residual pressure at all, the closeness of disc to pad would allow contact all the time, eventually ruining the pad/disc. So don't use a drum MC in any case on a disc brake system, unless the check valve is removed.

One other thing to note: The disc brake master cylinder flare nut fittings use different size threads than the drum unit. Unfortunately, these are not standard for the tubing size used, so if you bend up new lines from the auto parts store pre-flared tubing, the fittings will be wrong. You can buy adapters (you may have to search a while to find them), use the lines from the donor car, or bend new lines and reuse the fittings only from the donor car.

The drum master cylinder is divided into two reservoir compartments (for front and rear brake circuits); each reservoir is the same size. The disc master cylinder is also divided into two compartments, however they are different sizes. The reservoir for the disc circuit is much larger than that for the drums. The reason for this is different way that drum and disc brakes adjust for pad/shoe wear.

Drum brakes incorporate a self-adjuster mechanism which mechanically makes up for wear in the brake shoes. This self-adjuster is a screw mechanism which is positioned between the lower ends of the shoes and expands outward (like a turnbuckle) as the shoes wear to maintain the proper distance from the shoe to the drum.

Disc brakes typically position the caliper piston(s) directly behind the pad(s). As the pads wear, the piston must extend further out from the bore in the caliper, resulting in a larger volume behind the piston. This volume must be filled with brake fluid drawn from the master cylinder to prevent the inclusion of air bubbles in the system.

This is why the fluid level in the master cylinder of a disc brake system will drop as the pads wear, even though the system is not leaking. Obviously, this additional fluid needed to backfill behind the piston requires a larger reservoir on the disc side of the master cylinder.

While a drum master cylinder may work (and I would be concerned about differences in piston diameter), the fluid level would need to be checked frequently to avoid depleting all the fluid in the normal course of driving. Also, the manual brakes MC has a smaller piston and longer throw than a power MC. The power MC have a larger piston but shorter throw. Another way to think about it is that GM is always looking for ways to cut costs. If a single master cylinder design would have worked for both discs and drums, they would have taken advantage of the cost savings of only having to design and inventory one type. They still chose to have two different designs.

[ Thanks to Joe Padavano, Mike Rothe, Bob Barry, Dave Paulison, Dan Lacey for this information ]
Single to Dual Master Cylinder
To convert a 1966 98 from a single to a dual circuit master cylinder, I put on a power booster and dual master from a 1971 98 and it bolted right in, but I had to persuade my inner fender with a lot of strong blows with a hammer for clearance enough to run the hardlines. It worked, but the brakes never really felt like they had enough backpressure.

When you swap from single to dual master, you need to put in a variable brake proportioning valve. This keeps the right amount of pressure going to the rear brakes and keeps them from locking up first. Try Wilwood brakes; they also setup racing car brakes. You can tap into the rear line on the frame just behind the hydraulic front/rear splitter and bolt it to frame.

[ Thanks to Chris Fair for this information ]

Power Booster

Before adding a power booster to a manually braked car, consider whether there is enough vacuum to operate the power booster. The cam used in W-30'sand W-31's did not, so they cam with manual brakes from the factory.

Be aware that many power boosters are almost binary in nature (brakes either off or on), whereas manual discs allow for modulation. I have not noticed the requirement for excessive pedal pressure, either.

[ Thanks to Joe Padavano for this information ]

Racing Setups

If you want to spend the bucks on seperate rotors and hubs, again racing fabricators can set you up with just about anything you need. I recommend Coleman Machine, they have a very comprehensive catalog and reasonable prices. Check them out at
[ Thanks to Ken Snyder for this information. ]

Rear Axle Backing Plate Flange Bolt Pattern

The backing plate flange bolt pattern is the same on all GM passenger car RWD live axles from 1964 to today, drum and disc brakes inclusive. So I know caliper brackets will physically bolt up.

[ Thanks to Frank Evan Perdicaro for this information. ]

Rear Wheel Disc Brakes

I wouldn't convert the rear drums on my Delta if you paid me. The brakes on these cars are pretty good from the factory, I have no problem doing four wheel lock ups on pavement. These were two emergency stops in downtown Toronto which made me glad I'd spent the extra money on quality brake parts.

I really think trying to find discs for the back of your convertible is going to be a waste of time. The factory rear drums are 11"x(2 or 2.5", I can't remember) which are not small by any means. Rear drum brakes are MUCH more reliable in daily average use driving than rear discs, normally due to problems stemming from corrosion. Just ask anyone who owns an '88 thru '94 Cutlass Supreme (or any other FWD mid size GM for that matter), the rear discs on these cars are TERRIBLE.

This is what I would do to ensure your car has the best brakes possible without modification: FRONT: Start with high quality SEMI-METALLIC pads, such as Bendix METLOCK (fleet duty pads) or CarbonMetallic or even Raybestos PG Plus. Put in an installation kit(clips, bushings etc), new sliders, shims and of course, NEW rotors. Lubricate with COPPER antiseize compound and SILGLYDE. Make sure everything is properly lubricated to prevent corrosion.

REAR: Start with a high quality shoe, made by any manufacturer, such as Bendix or Raybestos. Get a combi-kit(includes hold down and return springs) and make sure your self-adjusting mechanisms are working properly. Replace them if necessary, otherwise lube very well to make sure they don't seize up later on. Buy NEW drums, even if the old ones are dimensionally OK on the inside. Often some of the fins fall off older ones causing vibration problems that are normally blamed on tire imbalance.

MASTER CYLINDER: If you even slightly suspect your master cylinder is bad, replace it with a NEW unit, not a rebuilt. For these master cylinders the price difference between new and used is so small that it's not worth going with a rebuild. Most of the time rebuilt masters are junk anyways.

I have done the above on my Delta, except for the rears (mine are still in excellent condition with AC Delco parts). You'll notice a difference with the METLOCK pads alone, but the new master cyl made the largest diffence in my car. Making sure everything in the rear is adjusted and lubricated properly is VERY important as well.

If your really gung-ho on upgrading your rear brakes, forget disc and go with the 12" drums from a station wagon or Cadillac. These brake were also available on our cars with the heavy duty J-?? axle option. I've seen these brakes on a Cadillac and they're huge! It's amazing how the one inch inside diameter makes the drums so much bigger. All you have to do is swap the backing plates I believe, but I've never seen anyone do it so don't quote me on this.

This whole thing about rear discs has me a bit perplexed. The front discs do most of the stopping. Spend your money there. Discs on the rear are neither easy or inexpensive to install, and WILL NOT help your braking very much if at all.

For $30 install the larger rear drums from a 1973-77 A-body onto your axle. Easy. Cheap. Damn near a bolt-on. Simplicity. Works 99% as well as discs for this application.

Examples and Parts:
I took the backing plate off of the 1980 TA and swapted it with the backing plate of the Olds. I did have to grind it down a bit because it was thicker where the bearing retainer is. Bolt pattern was the same, I forget the measurement. At the time I was running new style 15" ralley rims which rubbed the caliper a little. So I had to take a little off of the caliper. But all in all it worked, and looked cool when you look threw the rear rim and see disk's on a 72. I took this system off because the calipers were so dam expensive at the time, and both were frozen from sitting, no rebuilds were available. They were $180 each. I'm sure you can get them much cheeper now.

The first thing to look for is the flange type on your 86 rear end. GM used both 3-bolt and 4-bolt flanges on the G-body axle housings, while I'm pretty sure the 78 Seville (with an 8.5" 10 bolt with rear discs) used the four-bolt setup. While I'm sure the Seville used the 5 x 4 3/4 bolt circle, check the diameter of the axle flange and pilot on both your axles and the Seville. The pilot is the raised area in the center of the flange which fits into the center hole on the drum or rotor. As an aside, the original Sevilles were actually built on the Nova platform (supposedly the first time all five GM car divisions had sold the same platform) and thus used the leaf spring rear suspension. I also believe that this rear end will bolt in to a second generation F-body. BTW, that car doesn't have the fuel-injected 350 Olds motor, does it?

This month's Street Rodder magazine has an article on adapting Eldo rear discs (from a later Eldo) to an S-10 rear end (which I believe is similar to the late G-body rear ends). This S-10 setup used the 3-bolt axle housing flange and thus required the caliper brackets to be welded to the flanges. In addition, I seem to recall that some minor machining was required to the axle flanges to allow the rotors to fit.

Plan on using the adjustable valve in any case. If nothing else, your front-to-back weight distribution (well, your car's front-to-back weight distribution) will be different than that of the Seville. Don't forget that you'll need a disc/disc master cylinder as well (perhaps the very one from the Seville?).

I think you may have just hit on the key. The front to back proportioning valve setting is key to the performance of the brakes. It is very dependent on weight bias, weight transfer during braking, tire patch size, and brake capability. The F-body proportioning valve is almost certainly not optimized for an A-body application. An adjustable unit, properly dialed in, is mandatory. Even worse (and likely the source of others' frustration with rear disc conversions) is the use of the original disc/drum proportioning valve. This unit is _designed_ to limit the pressure to the rear drums to preclude premature rear wheel lockup; due to their non-self engerzing design, discs need higher line pressure than drums, so you can see the negative effect this incorrect proportioning valve would have.

The proper way to install rear discs is to remove the factory proportioning valve and install an adjustable unit in its place. As you also correctly point out, cars with the combination valve (proportioning valve, brake warning light switch, and junction block all in one housing) require this valve to be bypassed or replaced. I wanted to retain my warning light switch, so I used the configuration of the 69-70 cars with the separate proportioning valve - just use the _drum_ brake junction block from a 67-up car. This allows you to retain the warning light switch without any proportioning valve hardware. Plumb the new adjustable valve in series with the back brake line (the factory mounted a small cylindrical unit under the master cylinder) and away you go.

FWIW, You can get the backing plates for the rear disc for the Firebird (all 79-81 Birds, not Camaro, were available with rear disc) from GM NEW for about $50. The calipers are pricey, but if you don't care about emergency brake (can't say I recommend that!) you can use front calipers on the rear.

Calipers. 76-78 Cadillac Eldorado, and maybe Toro (help me out if you have seen this!! I have not confirmed it yet) had an optional rear disc. The Eldo/Toro rear caliper has a 2 3/8in piston.

1979-81 Firebirds. Available, all had 2" pistons.

Difference? Well, easy! The Firebirds mounted one caliper on the front of the axle, one rear. This was to clear the rear shocks (as they were staggered for axle twist control). The Eldo/Toro has them both on one side. The bleeder valves MUST be on top, the Eldo/Toro setup will bolt on 90% GM rear drive cars. The 78-88 G-Bodies mount the backing plate differently, so some work there.

A friend of mine has added this setup to his 1961 Pontiac Catalina. So yes, it fits the old 9.25 in Olds/Pontiac axle. Minor grinding on a hole or 2. Bolted up nice.

I have a complete (minus rotors) setup from a 1977 Eldo, I just haven't installed it yet. Make a nice fall project.

The 1979-81 Firebirds were some of the best stopping cars ever, having 11 in rotors all around, they did work. Again, valve proportioning was VERY important. Consider the Disc/Drum cars are 11in front, 9in drum rear. But my 1991 Bonneville Disc/Drum will easily outstop my 1991 Lumina with 4 disc. Just plain bad design!

The biggest reason is not braking power, it is FADE, disc brakes are very resilient to fade because they have far more surface area to give off heat. HP Books on brakes covers this very well.

If you did not change the master cyl, that is the problem. There is a residual pressure valve that keeps a constant pressure (1-2 psi) for the rear disc brakes. This is something in the design. Remove and all should ok, but to be correct, you need the master cylinder that has the capacity for the larger capacity of the calipers. A good one is the 1976 Corvette with MANUAL brakes, convert to manual brakes with 4 wheel disc, lose weight, and keep good braking feel!! The reservoir should have equal size front and rear on the 4 wheel disc cars.

[ Thanks to Warren Whitmore, Peter Sliskovich, Thomas Martin, Joe Padavano for this information. ]

1968 - 1972 Rear Discs:
There are a couple of ways I know of that you could do this, but one is only part of the needed system and the other will require extensive welding.

1) If this is just a race-only car, you could use weld-on caliper brackets that will allow you to use the same calipers both on the front and rear, along with some rotors from any of the better-known racing parts manufacturers. We have some of these on our stock car, and they work fine (but our car has a type 'F' rear end, the usual choice of stock car racers). The drawback is you don't have emergency brakes, an important option for the street.

2) You could find a rear end out of a GM F-body, and either cut the ends off that rear end that will have the disc brake parts (caliper brackets and E- brake cable mounts), or if the rear end track width is right have a competent (very competent) welder install the necessary brackets to mount it under your Cutlass.

What you are needing is a way to actuate your emergency brakes, which makes these calipers entirely different from the typical GM front calipers. These calipers cannot be compressed with a C-clamp like front ones are, the piston screws in and requires a special tool to do it right. The emergency brake cable causes the piston to screw out to lock the discs up I understand some Corvette rear ends use a small set of drum brakes in addition to the discs. I know our Mazda RX-7 uses the screw-in caliper pistons, and I found out the hard way.

These ways are not necessarily the only way to do this, and I'd also like to know any alternatives to what I've suggested, someday I'd like to put discs on the back of my 70 Cutlass Supreme.

Late 70's Trans Ams have a complete disc setup which should bolt on. The calipers have a parking brake provision, the brackets should bolt to the axle housing you have, and the rotors will slip over the lugs. The only thing is that the pilot hole in the rotor is slightly larger than the pilot on the axle shaft. This is the center hole in the rotor (or brake drum) that fits over the raised circular area on the axle flange. A simple machined ring pressed over the pilot on the axle flange fixes this. Unfortunately, I'm not aware of anyone selling these (which surprises me), but a machine shop can whip a couple up very cheaply.

[ Thanks to Ken Snyder, Joe Padavano for this information. ]

B, C-body Rear Discs:
1977-79 Cadillac Fleetwoods came from the factory with standard 4 wheel disc brakes. Therefore, it would seem the parts are available to convert any similar vintage GM (B or C-body) car to rear disc breaks by using a Fleetwood as a model.

The rear disc on the F-Bodies from 79-81 was a 2" piston, the 76-78 Eldorado's (Never saw a Toro with, but rumored to be an option) have the larger 2 3/8" piston, like the front brakes.

[ Thanks to Flynt Myrick, Thomas Martin for this information. ]


The only difference from 1969 to 1972 is that some cars used two-piece rotors (separate rotor and hub, held together by the wheel studs) and some used one-piece. The rotors are interchangeable, but I'm not sure which should be used where if absolute authenticity is important. All replacement rotors available today are the one-piece design.

[ Thanks to for this information ]

Silicone Fluid

Ethylene Glycol CH2(OH)CH2(OH) is a polar species, and thus will not dissolve in the non-polar silicone fluid used to "flush" the brake lines. In essence, picture oil flushed out with water. The oil will form discrete "pockets" where it can in the brake lines. In retrospect, Ethylene Glycol is more like water, and silicone more like oil, but the principle IS the same.

For those unclear on polar/non-polar; know what happens when you put gasoline in a styrofoam coffee cup? Styrofoam and gasoline are both non-polar. The gasoline disolves the styrofoam. Particularly amusing when the unsuspecting attempt to put gas down the carb with what is available.

What is needed for a proper "flushing" is for the lines to be flushed with a hydrophilic species that can readily be removed from the lines, and ~then~ the system be flushed with silicone.

I believe that the recommended conversion procedure is to rebuild the wheel cylinders, proportioning valve and master cylinder and flush the lines with 100% ethanol (or perhaps it was 100% propanol. I can't remember which) and blow them out with compressed air. You can't get 100% ethanol at the drugstore either, so perhaps it was propanol.

I hate to be a wet blanket, but with a system as critical as the brakes there is no substitute for doing the job right.

[ Thanks to Karl Aunan, Charles Dempsey for this information. ]

Single to Dual Circuit Master Cylinder Conversion

When swapping a dual master cylinder (drum or disc) onto a power brake car which originally had a single system (ie, 66 and earlier), the power booster will also need to be changed. Dual reservoir brakes were introduced in the 1967 model year. I suspect the A-body hardware is similar to that of the big cars.

Turns out that the single brake circuit cars use a significantly longer pushrod on the front of the power booster than the later dual-circuit cars. The good news is that I had a good power booster on the 1967 Cutlass parts car that bolted into the 1965 like it was born there. The later booster is an inch or two larger in diameter than the original unit, but it just clears the inner fender. The bottom line is that you will need to swap the power booster in addition to the master cylinder. The problem is that the pushrod on the power booster which operates the master cylinder is longer for the single reservoir units than it is on the dual reservoir units. Unless you completely disassemble your power booster and cut down the pushrod (which, by the way, only allows about 0.010" tolerance on the length), a replacement is required.

Also be aware that an A-body with a big block would need the notched valve covers. Installation of the wiper motor is tight but doable. I was hoping to retain the small booster on my 66 to allow the use of taller valve covers, but apparently not without modifying the pushrod. A quick comparison of the two master cylinders (after the fact, naturally) reveals that the single master cylinder piston has a much deeper hole for the pushrod than the dual master cylinder piston.

The other thing to watch out for is clearance between the new master cylinder and the hood. We used a 70 A-body disc brake master cylinder, which obviously is longer and thus comes closer to the underside of the hood. It clears, but the underhood pad will likely rub on the master cylinder cover, eventually wearing away that beautiful Eastwood Golden Cad paint. Note that aftermarket master cylinders may not use the same cover configuration as the original disc brake master cylinders (this one almost looks like a Ford cover - taller than stock), so you'd better check.

Another pointer: this 65 was originally a column shift car (since converted) and still had the linkage bracket bolted to the frame at the base of the firewall. We pulled that off, and lo and behold, the disc brake combination valve bolted right up to two of the frame bracket bolt holes - correct spacing and even the right thread! It's a little further back than stock, but conveniently appears to be out of the way of potential future headers.

Once you get past the power booster problems, you'll also need the distribution block from a drum brake dual reservoir car (I assume you're keeping front drums for now) and new brake lines from the M/C to the distribution block. The lines to the front brakes will likely need to be replaced, as they will be routed differently (and thus almost guaranteed to be too short) to reach the distribution block. The rear brake line will likely be a smaller diameter than the size for which the distribution block is designed (probably 3/16" vs 1/4"), so adapters will be required. Also, if you're bending your own lines, be aware that each port on the M/C and distribution block use unique (and non-standard) flare nuts to prevent incorrect installation on the assembly line. These parts are virtually impossible to get new, so plan on reusing old ones. The best bet is for you to find a donor car with the correct power booster, M/C, distribution block, and lines and grab it all. Even if you plan to bend new lines, you'll have all the unique fittings. Naturally, you should either plan to rebuild a junkyard M/C or get a rebuilt unit.

Some things to consider 1) Think about doing your soft brake hoses just for safety at the same time. Maybe hardlines too if they look suspect.

2) Carefully check the clearance of the dual circuit master against the inner fender well. You may need to persuade the fender with some hammer blows. Both my 66 big cars needed this when I swapped in dual circuit masters. The best thing to do would be to find a master which has engine side outputs, but I don't think Olds ever used these in factory applications. Be sure that the bore of the master you select is the same as the one you're replacing.

3) Go to a junkyard and get a dual circuit hardline junction block. There are old and new styles. Old is a rectangular block and was used from 67 or so up to the early 70's. New (maybe 1973 and later) is rounder on the corners. The piece you're looking for is square and has two inputs and three outputs with an electrical switch in the middle. When properly wired to your brake light, this switch will warn of loss of pressure during a problem.

4) Get an adjustable proportioning valve. Wilwood makes these and Jeg's has 'em. Maybe $50. Plumbing this in is the hardest part of the job, but it will allow you to control the pressure to the rear brakes after the swap. This is important because you want the front / rear bias to be correct. Can't recall now just which should lock up first.

6) I think pedal feel will be better if you use a brake booster which was made for a dual circuit master. I'm in the market for one now, so I can't confirm this. 67 and up is what you're looking for.

Great swap. It will increase your confidence in your brakes. Especially good if you do this _and_ put on front disks at the same time. Wow. What stopping power.

[ Thanks to Chris Fair, Joe Padavano for this information. ]

Fluid Resevoir:
I've had a dual master cylinder on my 66 98 for a long time for safety and to work with my disc brakes. About two years ago, I put on on of the modern ones (79 and later?) with the semi-see through reservoir, thinking it would be good to be able to see any drop in the fluid level. This conversion will work for A,B and C bodies with vertical (as opposed to canted) firewalls. This would include, oh, 65-70 big cars and the Cutlaii.

I used the master cylinder from a 79 Toro, whose reservoir was unfortunately molded for a slanted firewall. The problem in mounting those see through reservoirs on old cars is that they're molded to have the master cylinder pointing upwards, not flat. The years these were (and are) used all have firewalls which are slanted backward (towards the driver) which causes the master to point slightly upwards. So when you mount 'em on the older cars with vertical firewalls, you can only fill 'em half full or they spill over the front. My firewall is vertical, so I could never fill the reservoir full, because it would spill over the front when the rear was just getting full. Maybe you've seen these slanted reservoirs on late model cars where the master cylinder is higher in the front than the rear.

So there I am with a sort-of full reservoir that looks kind of funky for years, like it obviously doesn't belong there. Which of course, it doesn't.

I found one: The Pontiac Fiero. They pop right off with a long socket extension or big screwdriver. Messy, but effective. Suburbans have these flat ones too, but I think they have a physically longer and and larger master cylinder. Anyway a Fiero reservoir on a 79-82 Toro or Custom cruiser master cylinder will work.

I checked the swappability fit on a '82 custom cruiser master cylinder in the yard. It worked like a charm. Put it on my car in less than half an hour, no need to bleed the lines either.

[ Thanks to Chris Fair for this information. ]


It's not hard to bend and flare tubing, and the $35-$45 you spend on the flaring kit is far cheaper than the hours of labor you would pay someone else to repair the lines.

The disc brake master cylinder flare nut fittings use different size threads than the drum unit. Unfortunately, these are not standard for the tubing size used, so if you bend up new lines from the auto parts store pre-flared tubing, the fittings will be wrong. You can buy adapters (you may have to search a while to find them), use the lines from the donor car, or bend new lines and reuse the fittings only from the donor car.

[ Thanks to Bob Barry for this information ]

Vacuum Power Boosters

First, let me say that while I can't tell you what the differences in power boosters are between disc and drum applications, I have successfully used drum brake boosters with disc M/Cs on several occasions. Obviously, you'll need the correct master cylinder.

Yes, the early and later cars use M/Cs that look different, but I haven't found a functional difference. Again, I can't recite specifics about bore diameter, though a smaller bore will obviously provide higher line pressures. I suspect the bores are the same size.

Which proportioning valve do you have - the 70-earlier proportioning-only valve or the 71-up combination valve. The early valve has only two ports and is designed to be used in conjuntion with a separate distribution block like the one for drums. The proportioning valve was mounted below the M/C on a bracket and plumbed into the line between the rear brake outlet on the M/C and the distribution block. The combination valve has five ports and an electrical terminal, combining the proportioning valve, distribution block, and brake pressure switch into one housing which mounts were the drum brake distribution block was located. Either configuration works.

Some of your existing brake lines may be useable, however keep in mind that GM used unique flare nuts on all the lines to preclude incorrect assembly. In addition, the drum brake lines use different diameter flare nuts than their disc brake counterparts in some cases. Add to this the fact that you're guaranteed to break at least one of the lines during disassembly and I'm sure your looking at fabricating new lines. The alternative is buying a set pre-bent from an outfit like Inline Tube (who I highly recommend, by the way). 'Course, at that point, you MIGHTASWELL get their complete stainless brake line set...

I have converted 3 cars from drum to brake, all 3 were power assist. I left all the original boosters, lines, and proportioning valves and I have never had any problems. As long as the rear brakes are in good working condition and properly adjusted, the cars feel to me just like and other disk/drum car. I have tried both the early style and the later style master cylinders and even a drum master cylinder on disk brakes and I personally have not been able to tell the difference in any of them.

The early power booster will not accept the later master cylinder. Power boosters used with single reservoir master cylinders (66-earlier) use a longer pushrod than the 67-up boosters. This longer pushrod will push the MC piston too far in the relaxed position. You'll need to use a 67-up booster (drum or disc, it doesn't matter). While larger in diameter, the later booster will fit (we had to do this on Tom Simmons' 65 Cutlass). If you're running a big block, you may need to use the "notched" valve covers of the later cars to clear. Actually, the booster will fit with the un-notched covers, but you will likely have a problem if you ever need to remove them.

When converting from manual to power assited brakes, check the location of the clevis pin from the booster to the brake pedal. Power brake applications use the lower hole in the pedal for the clevix pin. If inadvertently installed in the upper hole (for manual brakes) the working angle of the rod is off and will be in a bind, causing a rock hard pedal and poor braking abilities.

[ Thanks to Stephen Hoover, Joe Padavano for this information. ]

Wheel Interference After Disc Conversion

After a disc brake conversion, I had to grind off a little of the corners of the disc pad backing plate for SSIs to fit. Note nothing instrumental to their structure or effecting function needed to be removed. Took about 1 minute per side with a grinding disc with the pads in place before the wheels were put on.

[ Thanks to Glenn Connors for this information. ]

Customizing / Alternative Setups

B, C, F, X Body Tall Spindles on A-Body

A good first step is to read a couple of articles about the swap:

The page at contains a write-up of Mick Gillespie's conversion to 12" slotted rotor, disc brakes on his 1969 Cutlass convertible. Lots of photos and descriptions of the step by step process. Also included are all the problems run into, and how they were solved them. It's under the tech section on the web page. Please check it out and give him feedback.

Mike Bloomer's page at gives you most of the details, and gives you some pics to go by. As far as what cars you can get the discs off of, 1970-81 F-body, 1973-77 A-body, 1975-79 X-body, etc. I would suggest pulling the whole spindle assembly as a whole. The reason being that I know some people that have run into problems finding the right replacement parts, and if you don't have the old one to match it up with, well you can imagine. I've done this conversion a few times, along with a few others on the list and there are a few ins and outs to doing the swap and I'm sure we can answer any questions.

Check out and for some very useful information on the conversion, including a list of donor cars.

A complete writeup on the B,C,F,X-body spindle swap conversion is at: .

Components for these swaps come from the 1970-81 F-body, 1973-77 A-body, 1975-79 X-body or 1977-up B-body cars originally equipped with the "sister" 11-inch Components.

The 1973-76 A-Body spindles will not fit on a 1964 to 1972 A-body correctly (or safely) without the custom upper and lower ball joints available from Hotchkis or Global West, as the tapers on the ball joint studs are different.

Some 1976-later fullsize passenger cars (typically police cars, station wagons or heavy-duty towing packages) used 12" rotors with a 5x5 inch wheel bolt pattern. The caliper was the same, but the spindle was different. For the ultimate in braking, the larger rotor and spindle can be used if desired with convertion kits.

The 1967 to 1969 and 1968 to 1974 Camaro/Nova (which includes the Oldsmobile Omega) used the same spindle, but the steering knuckle is a separate piece. There are three bolts on the disc and drum spindle, and the spindle assembly for discs (Camaro/Nova) will fit into a 442, but the steering arms must be changed.

12" rotors from the B-body will fit your spindles, but if you want the A-body bolt pattern (5x4 3/4) and not the B, C full size pattern (5x5), you have to use the rotor from 1LE F-car (part# 18016035). You could also redrill B, C 12-inch rotors for the 5x4 3/4 bolt pattern.

The F-body spindles were taller and would change the geometry of the front end. This would raise the roll-center from 2" below ground to 2" above ground. Camber is changed from +½° to -½°, caster is changed from +½° all the way to -3½°!

Using F-body dics brakes on A bodies requires about 1" of shims on the control arms to get correct alignment settings. The solution to this problem is to buy the special offset upper control arm shafts that are (were) available from HO racing. I assume they are also available from NAPA or the like. These shafts are offset to compensate for frame sag on old cars, since in that condition, you can remove all of the shims and still not be in specs. By installing them backwards (i.e. with the offset towards the frame), you can eliminate the vast majority of the shims!

Hot Rod tested a 1964 GTO before and after. The after test had 16" wheels and peformance tires. This car was put on a skid pad and recorded a 0.96G, which was equal to the newest Vette, and better than an IROC Camaro!

A listee made this change to a 1967 Chevelle, and has to say that the change was startling. He had to learn to drive the car once again. The suspension is very fast, and he had to add a faster steering box from a '72 Cutlass.

As an alternative to using the F-body knuckle, consider using the knuckle from a GM full-size wagon with 12" rotors. The increased knuckle height is the same, and so is the ball joint/tie rod end, but by using the station wagon knuckles, you can use the early-90's 1LE Camaro 12" super beefy rotors (which have a 5" x 4.75" bolt pattern). For 12" front disc brake conversion, the PN for the station wagon knuckles I used is 369055LH/RH.

The caliper/pad is the same as the standard A-body disc caliper, and you have 12" front disc brakes. This conversion gives outstanding results. Switching to all urethane bushings, TRW 70 442 w/o AC coils (500+ lb rate) and 245/60 VR15 Eagle Gatorbacks on 15 x 8 wheels (minimum of 15" wheels are needed for the 12" brakes). Handling is top notch. A Vericom accelerometer mounted in the side window (for skidpad measurement), showed low .9G for a 1970 GTO, with stock sway bars and 255/60 VR 60 Eagle Gatorbacks.

I did a disc brake conversion to my '72 Supreme using Mondello's mini-booster/master combo. It wasn't an easy bolt up proposition, but the results are great.

[ Thanks to Tom Lesniak, Chris Smetana, Scott Mullen Trevor Lee, Mike Bloomer, Joe Padavano, John Carri, Mick Gillespie, Stephan Hoover, Roger Peterson, Jonathan Parke, John Monnin, Kerry Kroger, Trond Jarle Trond Pedersen for this information. ]

Tuning / Examples

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