In 1964 the F85 had another ratio marking (example: P3.08L). It is on the right rear inboard side of axle houlsing tube. "P" is vendor; 3.08 is ratio; "L" means locking axle. Axle ratio codes are located as follows:
Full size models: 1959-63 On carrier casting lower locating boss. 1964 exc Jetstar 88 On carrier casting lower locating boss. 1965-69 exc Toronado Stamped on right rear inboard side of axle housing tube. 1966-67 Toronado Ratio and date code stamped on the flange below fill tube boss. 1968-69 Toronado Ratio and date code stamped on flange near RH spreader hole.
F-85 and Jetstar 88:
1961-64 On right side of housing cover. 1965-69 On right rear inboard side of axle housing tube.
Ribs on Differential:
Look at the rib(s) cast into the side of the center section. If there is only one rib it is a "B" Buick rear. If there are two converging (towards the front of the car) ribs it is a "P" Pontiac rear. The single rib rears are much weaker than the two rib versions. Among other things, the number and size of the pinion gear splines are smaller.
On each GM differential, there is a code on the ring gear which shows the number of teeth, and therefore the ratio. Remove the rear end cover and read it, then use the table above to figure the ratio. Or do the long division.
Please refer to the
Differential Codes section for
|1959 - 1964:|
|All except Jetstar 88||2.69||43-16||2|
|Dynamic 88, Delta 88, Starfire, except Police||2.73||41-15||QA||QB|
|except Vista Cruiser||2.78||39-14||SA||SB|
|except Vista Cruiser and Police||2.78||39-14||SA||SB|
|Vista Cruiser except Police||3.08||37-12||SM||SN|
|Jetstar 1, Dynamic 88, Delta 88, Starfire||2.73||41-15||QA||QB|
|Dynamic, Delta 88||2.73||41:15||QA||QB|
|Jetstar 88, except Police||2.78||39-14||RA||RB|
|Vista Cruiser except Police||3.08||40-13||SM||SN|
|Note: Codings not available on '66 4.11-1 (37-9), and 4.33-1 (39-9).|
|except Vista Cruiser and Police||2.78||39-14||SA||SB|
|Note: Codings not available on '66 4.11-1 (37-9), and 4.33-1 (39-9).|
|Jetstar 1, Dynamic 88, Delta 88, Starfire||2.73||41-15||QA||QB|
| With heavy duty 15" wheels & hubs & drums.|
|98||2.73||41-15||QK, RO||QL, RP|
|3.08||40-13||QM, RS||QN, RT|
|3.23||42-13||QO, RU||QP, RY|
|3.42||41-12||QQ, RW||QR, RX|
|Delmont 88 w/330||2.78||39-14||RA, QV||RB, QU|
|3.08||40-13||RC, RI||RD, RJ|
|3.23||42-13||RE, RK||RF, RL|
|Delmont 88 w/425, Delta||2.73||41-15||QA, RO||QB, RP|
|2.93||41-14||QC, RQ||QD, RR|
|3.08||40-13||QE, QY, RM, RS||QF, QE, RN, RT|
|3.23||42-13||QG, QW, RG, RU||QH, QX, RH, RV|
|3.42||41-12||QI, QS, RW, RY||QJ, QT, RX, RZ|
|except Vista Cruiser||2.78||39-14||SA, S2, SK||SB, S3, SL|
|3.08||40-13||SC, S4, SQ||SD, S5, SR|
|3.23||42-13||SE, S6, SV||SF, S7, SW|
|2.41||41-17||SS, SU, ST||TA, TS, TB|
|3.42||41-12||TL, S8, TP||TM, S9, TQ|
|3.91||43-11||TN, T2, TU||TO, T3, TV|
|Vista Cruiser||3.08||40-13||SM, T4, SG||SN, T5, SH|
|3.23||42-13||SO, T6, TC||SP, T7, TD|
1968: Model Ratio Teeth Open Anti-spin Type "O" differential except Vista Cruiser and 442 2.56 41-16 R2, R6 R3, R7 2.78 39-14 SA, S2 SB, S3 3.08 40-13 SC, S4 SD, S5 3.23 42-13 SE, S6 SF, S7 3.42 41-12 TL, S8 TM, S9 3.91 42-11 TN, T2 TO, T3 Type "C" differential 2.56 41-16 R8, TR R9, TW, TH 2.73 41-15 RA, TT RB, TJ 3.08 43-14 RC, T4 RD, T5 3.31 43-13 RE, T6 RF, T7 Vista Cruiser w/400, 442 4.33 39-9 TW, TY Vista Cruiser w/350 3.08 40-13 SM SN 3.23 42-13 SO SP 2.78 39-14 TA TB 1969: Model Ratio Teeth Open Anti-spin Type "O" differential except Vista Cruiser 2.56 41-16 R2, R8 R3, R9 2.56¤ 41-16 R6 R7 2.78¤ 39-14 S2 S3 3.08¤ 40-13 S4 S5 3.23¤ 42-13 S6 S7 3.42¤ 41-12 S9 2.78 39-14 SA SB 3.08 40-13 SC SD 3.23 42-13 SE SF 3.91¤ 43-11 T3 3.42 41-12 TM 3.81 43-11 TO 4.33 39-9 TY Type "C" differential 2.78 39-14 RA RB 3.08 40-13 RC RD 3.23 42-13 RE RF 3.07¤ 43-14 T4 T5 3.31¤ 43-13 T6 T7 3.55 39-11 TL 3.73 41-11 TN 2.56¤ 41-16 TR TH 2.73¤ 41-15 TT TJ ¤ HD brake (Police) or Disc. Std brake Delmont 88 w/350 2.78 39-14 RA RB 3.08 40-13 RC RD 3.23 42-13 RE RF Delmont 88 w/455, Delta 2.73 41-15 QA, QK, QS QB, QL, QT 2.56 41-16 QC, QQ QD, QR 3.08 40-13 QE, QM, QY QF, QN, QZ 98 2.73 41-15 QA, QK QB, QL 2.56 41-16 QC, QQ QD, QR 3.08 40-13 QE, QM QF, QN Toronado 3.07 43-14 T Vista Cruiser 3.08 40-13 SM SN 3.23 42-13 SO SP 2.78 39-14 TA TB Delta 88 w/350 2.78 39-14 RA RB 3.08 40-13 RC RD 3.23 42-13 RE RF All Delta w/455, std. brakes, 98 optional 2.56 41-16 QC QD 2.93 41-14 QI QJ All Delta w/455, h.d. brakes, Police or disc brakes, 98 standard 2.56 41-16 QR 2.93 41-14 QU QV 1970: 1971: 1972: 1973: 1974: 1975: 1976: 1977: 1978: 1979: 1980: 1981: 1982: 1983: 1984: 1985: 1986: 1987: 1988:
1969 - 1970
All 1969 O axles use a sealed ball bearing as you describe. The 70 O axle uses the bearing/seal as you describe. They are not interchangeable. The Vista Cruisers use a larger bearing and are not interchangeable with your Cutlass O axle. There was a design change from 68 to 69 VC axle bearings - hence the note in the chassis manual. To replace the axle from a 69 SA code (2.78) Cutlass, you need to find an axle from a 67-69 Cutlass series (Not V/C or Canadian built). With a ratio between 2.56 and 3.23.
1978 - 1988
First, ALL GM 1981 to 1988 G-Bodies used a 7.5" ring gear rear axle EXCEPT: Monte Carlo SS - 7-5/8" 3.73, Olds 442 - 8.5" 3.73, T-Type and Grand National - 8.5" 3.42 or 3.73. The 8.5" axle is the same used in the B-body (full sized) except a shorter axle tube length. Second, the 7-5/8" axle is actually used in the mid 80's F-bodies Camaro & Firebird. This axle is the one used in the Monte Carlo SS. Third, the '80s S and T trucks use a 7.5" ring gear axle. A short trip to the service manuals on these vehicles is all it takes to check this information out.
The 442 and Regal axles are hard to find because 442s are rare and most T-types and Grand Nationals are not junked yet. For older Cutlasses, the B-body 8.5" axle might fit better than the G-body axle.RPO |--------Axle Code--------| Ring Gear Code Ratio Conventional Limited Slip ------------------------------------------------------- 7.5" G72 2.14 2AK 2BK (aluminum brake drums) 7.5" GH2 2.29 2AH 2BH 7.5" GU1 2.41 2AJ,2AZ 2BJ,2BZ 7.5" GM8 2.56 2AA 2BA 7.5" GU2 2.73 2AB,2AX 2BB,2BX 7.5" GU4 3.08 2AC,2AV 2BC,2BV 7.5" GU5 3.23 2AD 2BD 7.625" GT4 3.73 2TF 2TH (Monte Carlo SS) 8.5" GU6 3.42 3TP 3TJ (T-Type, GN Std.) 8.5" GT4 3.73 3TG,3TE 3TR,3TX (442, GN Opt.) 8.5" GU2 2.73 8YB 8YP (B-Body) 8.5" GU4 3.08 8YD 8YR (B-Body) 8.5" GU5 3.23 8YE 8YS (B-Body)
If you don't have the codes with you to indentify if it is an 8.5" or not, I found that if you measure the distance between the very bottom bolt for the cover and the next adjacent one (either right of left), it will be 3 ¾" for a 8.5" and 3 1/4" for a 7.5".
All 1978 and up Olds came with 7.5" 10 bolts, no 12 bolts (Chevy or Olds) whatsoever. So guys with 1978 and up G bodies had a few options: beef up the 7.5" with better axles and a good posi unit, or find an 8.5" out of an 83-84 HO, 85-85 442, or 84 and up T-Type or GN, or go with a Ford 9" from Currie or Moser, or buy the control arms from Southside traction and install an older 1968 or so Chevy 12 bolt or 10 bolt.
A friend of mine just old me that the 1964 to 1967 A-Body cars ("intermediates") rear end will bolt into a G-body Cutlass with minor love taps to the upper trailing arms. He said it is ½ inch wider on both sides, but other than that, it is the 8.2 inch 10 bolt. Much stronger than the 7.5in. And no matter what rear end I find it will have better gears than my 2.14's!
The 1968 to 1972 A-body differential will bolt up. Summit sells a control arm set that will properly adapt them.
Be sure to get the driveshaft with the rear end, since it is well - 1/2 inch shorter. Also get the rear anti-sway bar that links the lower control arms, to help your 60 ft. times. Posi-traction units are available from Auburn Gear works for about $295 for clutch type and $395 for the better cone type units, in case you get find a reasonable priced differential with open gears. A number of places sell 8 1/2 in. gear sets for changing ratios.
The 3.73 should have been available in the 442's, (hopefully the 442 guys can substianiate this, and give you differential numbers to look for) and the Turbo Regals had 8.5 inch rear ends with 3.42 gears standard and 3.73 optional from 84 through 87. Earlier years had reported optional higher ratios in 7 1/2 inch units (sometimes the information in the American Musclecar Publications should be taken with a grain of salt). On the front of the right axle tube the second and third codes should be TJ (for open rear end) and TP (for limited slip differentials). There may be a little tag on one of the bolts on the cover indicating the need for limited differential fluid, but do not rely on that.
The 7 1/2 inch units look similiar to the 8 1/2 inch units from the outside, but most publications show a more rounded cover for the 8 1/2 inch unit. Having had the units side by side I could barely tell the difference. They both are 10 bolt covers. The mounting points for the upper control arms hang out more on the smaller units, maybe a half inch !
[ Thanks to Chris Fair, Bill Culp, Steve Ochs, Tom Millard, Loyd Bonecutter, Thomas Martin, Charley Buehner for this information ]
Gearing is much less than an exact science. I definitely don't have any concrete answers for you here. I can only give my thoughts and assumptions, and the directions I'd consider. What you end up doing is up to you only, and either way you go, it should end up fast ('cuz it's an Olds, and that's inherent in the design, right?). The gearing and RPM range of the motor will just dictate when that fastness is most noticed.
What do you want? Good street performance or 1/8 or1/4 mile performance? If you want good street performance gear it so you keep the rpm's in the optimum power range of your motor at your typical cruise mph. If you want straight line performance gear it so that the motor is at the top of the power band at the end of the track. You also want to make sure that your tires can handle the extra torque that a steeper gear will create at the tires.
Running 3.23's, I think it's too steep for a BB and the highway. For racing, though, I'd go a bit steeper. 3.50's might be fine, or 3.73's might be where to shoot for. It will probably all boil down to your engine's redline. If your engine can stay at 8,000 RPM for a while without the mechanical rev limiter (aka rod) taking over, then the steeper gears will be great. The 455's usually don't get that high, though, (without BIG$$$) which should leave you topped before 6000, I'd assume. With 4.11's and that range, I'd guess you'd likely be topped out before the end of the quarter, I'm not sure. My GS with the 3.42's goes through at just over six, usually, but its RPM characteristics are markedly different than the Olds was for me. OTOH, with the really steep gears, you'll top out faster, but you'll have alot more speed keeping you going. You'll only go 100 MPH, but you'll be there alot sooner than the other guy, and he'll still have trouble keeping up, even if he goes through the traps at 120 MPH.
I guess in my eyes, it will depend on what RPM range your motor produces it's torque. If you'll have monster low end torque, but limited high end, then a lower (numerical) gear would probably be better. If you have a lot of power at lower RPM's, you may be happy with a 3.23 to 3.55 gear, and still maintain highway drivability.
If you have nothing but high end power, than the motor will need all the help it can get to get the sled moving, so the 3.73's and higher (numerically) would be a better choice. You need a 3.73 - 3.90 gear in order to get the RPM's up high fast. With 3.90's and 245R60/15's you are turning 3500 RPM at 60 MPH.
If you plan on streeting it, you'd want to modify those numbers a bit, too. I'd have a hard time recommending anything steeper than 3.73's for the street, unless you get an overdrive in there. It'll drive ya nuts on the highway. It looks like with the proper selection of tires, you'll have no problem locking them onto the pavement. The stall and gears will like that.
The rear end gears you pick depend on what you want the car to do. The Dart's 3.55's and high RPM HP isn't too practical for around town (35mph-45mph speed limits), because to enjoy it, it has to be wound out too much, which results in going too fast when really enjoying it. 3.73's or 3.90's would be better suited for this car for power, but it will kill all highway drivability.
I recommend 3.23's highly. I like the good combination of torque at lower rpms, and gas mileage that is acceptable.
If you're running a tall tire (30"+), then you need to take that into account in your gear selection. That 3.50 gear and a 27" tire might be the equivalent of a 3.00 gear with a much taller tire. Figure what RPMs you can live with at highway speed, and then figure out what gears will put you there with your tire and tranny selection (you might have to go with 4.56's to get you there with a tall tire).
1970 Buick GS Stage 1 with a 3:23 posi. Used for 3 years as a family car. The RPMs were not objectionable at all; my wife never complained. The car was always quiet & smooth. I believe that I was turning a little under 3000 RPM (27-2800?) at 70 MPH. Gas mileage was 14 MPG on the highway.
1973 Vista Cruiser w/455 & a 3.23 posi was always very quiet at 70 MPH & (after modifications) got 14 MPG on the highway. The Vista Cruiser was owned for 13 years with 130K miles on it. It was used often for trailering long distances.
1962 Jetfire with a 3.31 diff is just fine as far as highway engine noise. The 1968 442 has a 3.91 posi which is far too noisy at highway speeds. I am trying a 3.42 posi diff in my current 1970 GS, hoping that I will like it. It may be borderline though.
1964 Olds (330/4V) is a 3.36 diff and 215R70/14's: the 3.36's are a good mix of matching the 330's mid range torque and high RPM HP with a drivable car on the freeway. It turns 3,000 at 60 MPH; good passing, 40-70 MPH (kick down 2nd gear) acceleration is a lot of fun.
1969 Dart (built 318/4V) with a 3.55 diff and 225R70/14 tires. The engine is built for high RPM HP, it has nothing below 3000 RPM. The torque comes in at 3,000 RPM, and the the HP come in at 4,000. It turns 3,200 RPM at 60 MPH.
1974 Plymouth Satelitte (440/4V) with a 3.23 diff and 255R60/15 tires: tons of low end torque match the 3.23's at 35 MPH to 90 MPH (with 2 gear changes) quite nicely. The 3.23's allows a kick down to second at 50 MPH. This thing is a monster between 45 MPH and 70 MPH. (ex-cop car).
1970 4-4-2 with the standard 455 (mildly modified) and 3.23 diff. At 60 MPH, I could punch it and instantly pass anything I ever met. Yet the RPM's were comfortably in the 2500-3000 range.
Cutlass with 3.42's and 25 in. tall 235/60/14 tires. It turns about 2700 RPM @ 60 MPH. I like the 3.42's for all around performance and driving ease.
Why compromise? Go with the overdrive transmission and keep the 3.73s! Alternatively, get a Ford 9" and two center sections, one with 3.91's and one with 3.08's. Switch gears for your upcoming driving needs.
I have 3:91's in my H/O and, while the engine tachs out on the freeway, I don't mind the noise (I'm on the far end of that tolerance scale).
Actually, have you really considered the cheapest way out? Get a set of tall rear tires for highway cruising. This will effectively give you a lower numerical rear end for improved highway mileage and reduced rpms. Just swap the shorter tires for strip terrorizing. The only problem is that your speedo will be wrong with at least one of these configurations!
BFG makes some T/As for street trucks which are pretty tall (up to 35" diameter, which obviously won't fit in your wheel well). These are not the off-road tires which most stores stock, so you may have to order them.
[ Thanks to Doug Ahern, Charley Buehner, Bill Culp, Joe Padavano, Dave Wyatt, Bob Barry, Daren for this information ]
And Anti-spin Swap
With the replacement rear end OUT of the car: Unbolt the retainers on the ends of the housing. Get an axle puller (Auto Zone will loan one to you) and jerk out the axles. Clean those nasty axles, press off the old bearings and retainers and press on the new bearings and retainers. Then go put those axles in the corner. It will be a while before you need them. But first go try to stick them into the posi carrier you have to make sure the axle is the right diameter and has the correct number of splines.
Next remove the old axle seals and replace them with new ones. You will need a seal puller or a slide hammer with an attachment. The seals are pressed in the end of the axle housing. The best way to press them back in is to find a socket that is rhe right diameter and hammer them back into the axle tubes.
Next unbolt the cover plate and drain out all that old fluid. Next you have to pull out the old carrier. Clean off the caps that hold on the carrier with a good degreaser like alcohol. Then before removing the caps be sure to mark them as right and left or whatever. Be sure also to know which end is top and bottom. I used fingernail polish. Markings is necessary because these bastards are line bored after assembly. This is line bore thing is important to remember. Now take out that greasy carrier. You may have to pry it out. It also helps if you turn the pinion gear it will help lift the carrier out of the housing.
Now it is time to take out the pinion gear. The hardest thing will be getting the pinion nut off. I would soak it down with WD 40 or Liquid Wrench. Then get an impact wrench to get the pinion nut off. Of course you will have to find some way of keeping the pinion from turning. Once the nut is off, get a big hammer and smack the pinon gear. It will eventually come out of the housing. Do not screw up and smack the yoke.
You mihgt want to get a piece of wood and put it on the pinion and hit the wood instead of trying to hit the rear of the pinion while trying to miss the yoke. Once the pinion comes out, pry out the pinion seal. You can do this with a dull chisel or screw driver.
Next you will have to remove all of the old bearing races from the housing. There will be a notch in the housing at the rear of the race where you can get a punch in there to knock out the race. Actually there will be two notches. Now press the new bearing races into place. For this I found some really big sockets and an extension. I put the socket on the race and proceeded to hammer away. This was a major PITA for me because the rear end was still in the car. There are two bearing races in the carrier. The rear and front pinion bearings. Now get your new posi carrier and press the bearings onto the carrier. Go ahead and put your ring gear onthe posi carrier if it is not already on there. Be sure everything is clean. Be sure to put in the new pinion oil seal.
Now the fun begins. If you have a richmond gear there will be a check distance engraved on the face of the pinion gear and a backlash measurement engraved on the ring gear. These are CRITICAL numbers. If not you will have to use some general numbers. I think factory backlash is .005. My Richmond gear backlash was to be .008. If you have too much backlash you will know in a hurry. When you drive down the road and let up onthe accelerator you will get one loud whine.
The check distance is the distance from the centerline of the ring gear to the face of the pinion gear. This is one MF to measure. Technically you cannot do what you think is right. That is: lay a flat piece of metal across the face of the two caps and measure down to the face of the pinion. The reason this is not accurate is because the saddles are line bored. The caps are not exactly split in 1/2. Unless you have a pinion depth setter, you may just have to use the above method and hope for the best. However, if you do not have a check distance dimension you will just have to do it like this. I am going to ASSUME that you do not have a check distance dimension. In that case do the following:
If a shim came off of the pinon gear, put it back on the new pinion gear. Then press the rear pinion bearing up on the pinion shaft untill it is tight against the rear face of the pinion and shim. Then put the crush sleeve on then put the front pinion bearing on. The front pinion bearing is not pressed into place. It is held in place by the yoke. Then slide this mess back into the housing, put the yoke on and tighten it up slightly. You tighten up the yoke untillit takes about 15 INCH pounds to turn the pinion gear. OK assume this is done.
Now it is time to put the new posi carrier in place. Try to hold the races on the bearings and put it in the saddles. The ring gear should engage the pinion nicely. Now comes the trial and error BS. You put shim packs on each side of the carrier untill you get the proper backlash on the ring gear and the proper paint pattern. Once you THINK you are close, get some gear marking compound and apply it to the ring gear. Be sure to put your caps back on and torque them to about 65 FOOT pounds. Double check that torque I am doing this from memory. Once you have everything in place and painted up turn the pinion gear and see what pattern you get on gears. You are looking for a rectangular pattern that is even across the drive face of the ring gear. I am sure it will not be right the first time. Now you get to move shims from side to side untill the pattern is correct. Then check the backlash. I kinda did mime backwards. I got the backlash right and then checked the paint pattern. It turned out to be perfect when the backlash was correct. I also was able to measure my check distance before I ever put in the carrier. But I am assuming you can't.
Once you have the paint pattern anb backlash correct, you are good to go. Put everything back together and drive off. And listen. If you have strange noises. TRY AGAIN. Be sure to use a good lube and put the limited slip additive in there or you will get chatter and grabbing and such. Do not use synthetic gear lube!
The most critical part in all of this is getting the correct gear teeth mesh. Take your time with those shim packs. Of course if you have crappy luck like me and your pinion depth is wrong, you will be screwed. You will have to take the pinion gear back out and put in the right shim to adjust the depth of the pinion in and out.
[ Thanks to John Harris for this information ]
Clutch Plate Anti-Spin
I can see no reason why a rebuilt clutch plate type posi can't be rebuilt good as new. This assumes no obvious mechanical failures which would otherwise render the unit useless. It is/was common practice among drag racers to take a brand new unit and tighten it up as much as possible by using thicker plates and other means. If the car is street driven, you must use gear lube formulated for posi units.
[ Thanks to Bob Handren for this information ]
Cone Plate Anti-Spin
It is also a cone type posi unit. If that is shot it cannot be rebuilt in the same fashion as the plate/friction type. They can however be made functional with a little work.
[ Thanks to Bob Handren for this information ]
General: The prices you were quoted for gears are about twice the going rate it you buy direct. Usual practice is to double the cost if you ask someone else to order 'em for you.
For most applications, gear and carriers are available, but cases are not.
1967-1970 "O" Axle Overhaul Kit:
Until now, many items required to properly overhaul an O axle were unavailable (Chevy 12 bolt parts do not interchange). Which meant reusing the old parts. This often results in premature bearing wear and shortened ring & pinion life. Our new kit includes the following items required for a complete differential overhaul and/or ring & pinion change: carrier bearings/races, pinion bearings/races, ring gear bolts, our new crush sleeve, case side shims, pinion lock nut, marking compound, Loctite pinion seal, cover gasket and sealer.
Available for all 1967 thru 1970 (A body) O axle 12 bolts. Open or Anti-Spin. Specify year and ratio. Complete kit priced at $159.95. Available only from the mechanical parts specialists at Supercars Unlimited. Where Cutlass/442 is ALL we do!
8029 A SW 17th
Portland, OR 97219
PH: (503) 244-8249
FX: (503) 244-9639
"O" Axle Parts:
Check with the gear suppliers that advertise in just about every worthwhile auto magazine. Ring and pinion gears are now available also. Either Perfection American or Zoom. A great dealer I have used it Drive Train Specilaties (DTS). They (as well as others) even have the shims, bearings, seals and gaskets in kit form so the rear can be set up properly.
28 Spline Axles:
If the differential has 28-spline axles, Reider Racing (313/946-9231) can fix you up.
31 Spline Axles:
If the diffential has 31-spline axles, you'll have to find an original unit and have it rebuilt.
[ Thanks to Brad Nicholson, Bob Handren for this information ]
Gears are available for most every differential. But buying and installing a bunch of parts can get expensive - fast. It would probably be a bunch cheaper in the long run to find the rear with the gears and anti-spin that you want.
This table works in the opposite direction ("year to" to "year from") as well.
Year From Year To Model(s) Comments 64-66 64-66 GM A-body - Cutlass, Chevelle, LeMans, Skylark Bolt in. 67 64-66 GM A-body Lower spring perch is different, requiring the use of the 67 springs. 68-72 64-66 GM A-body Axles are about an inch wider than the earlier ones and also have the control arm mounting locations in a slightly different place; the axle will physically bolt up to the early car but the pinion angle will be wrong.
[ Thanks to Joe Padavano for this information ]
To upgrade an open differential to a posi, you must change the carrier to a posi type. That is, just the "guts" inside the rear end. You can even keep your existing gear set. A new or rebuilt unit should be about the same in durability. If you have a regular "C" type rear end then parts for this are very easy to find. However, if you have a "O" type rear end used in 1967 to 1970 models then a posi carrier is very difficult to find. Best bet is to get a rear end specialist to do the work.
An entire rear end from another GM product is a bolt-in fit as long as you're doing it in the same body style. Minor differences such as brake lines and U-joints are the only trouble spots. Buick, Olds, and Pontiac rear ends are interchangable if they are the same frame size (an "A" body GTO rear will fit in a Cutlass).
In regards to swapping 1964 to 1967 A-body 10 bolt rear axles, with 1968 to 1972 A-body axles, the entire housings will swap. First of all, the 67 and 68 Type-O axle housings carry exactly the same part number (don't know about Type-C axles). Regarding the 1968 and up axle being wider, I first heard about this width difference (which was more like an inch, not 1/4") in Car Craft about 20 years ago. I sometimes wonder if this isn't in the same catagory as the notorious "offset engine mounts" allegedly in the Supremes.
A couple of things you do need to look out for, however. First, the early axles (1964-66) may have slightly different mounting points for the control arms. Installing these in a later car with the late control arms could result in an incorrect pinion angle and the attendant U-joint wear, unless you use the control arms that go with the axle. Second, some axles (for example the 1971-up corporate 10-bolt) have a different dimension from the u-joint flange to the axle centerline. This will sometimes require a slightly different driveshaft length. I ran into this problem when I installed the axle from a 1972 442 into a 1968 Malibu. The Chebby driveshaft was about an inch too long.
As a general rule, most of the axle shafts will swap as long as they have the same spline count. This excludes 10 bolt "C" axle shafts (as in Ch*vy) which are unique in that they have an internal "C" clip to retain the axle in the housing and use a roller bearing in the tube end. This is as opposed to a bearing which is pressed onto the axle and then bolted to the tube end as most other sane manufacturers do.
Most GM diffs carriers carry ring and pinion sets up to 3:42 ratio, from 3:73 and up you have to change the carrier. The reason is that as the pinion gets smaller (with the lower gear ratio), the deeper the crown gear has to be. Instead of making extemely thick crown gears, GM made two types of carriers instead. Some after market suppliers have a spacer which allows you to put a 3:73 gear set on a 3:23 carrier. I have done this before on several cars than run both on the street and the strip, and don't want to change the carrier.
As for gear combo, say if you had just a posi carrier with say a 2.73 gear, you could put a 4:10 gear or even 4:33. Consult the chassis manual or the gear manufacturers catalog for compatible gearing. The only thing you will need to do is buy a shim kit because when you put higher gears on the carrier, the carrier shifts relative to the pinion. These shims go between the carrier bearings and the start of the axle tubes in the housing.
The service manuals from 1967 and 1969, and also the illustration section of part listings from that era, have pictures and diagrams of the center section castings (using the ribs to ID the rear) and rear covers (Chevy rears have that goofy wrinkle).
If you have an old bearing handy, it has the # on the race that can be used to get a replacement. This # is a standard that can be found in any bearing parts shop or even at the usual auto parts place that you frequent.
[ Thanks to Bill Culp, Joe Padavano for this information ]
The big question for swapping the internals is of course, just what did the new internals come out of. Many cars being very close in model year used different internals, even though the cover on the differential has the same number of bolts. Identify what you have first.
You need a few tools to do the swap correctly:
- Impact gun, for loosening and tightening the pinion nut
- Dial indicator, for setting gear backlash
- An inch/pound torque wrench
- Pinion depth guage (no, you won't find that one at Pep Boys or AutoZone)
If you don't have these tools, you can buy a set of ring & pinion installation tools for $150-$200, and an impact gun would run you around $90-$120 for a cheap one (of course, that is assuming you have an air compressor).
Now if you have or can borrow all the tools, the critical things to measure are the pinion depth, pinion bearing preload, carrier side clearance, and gear backlash. These are all outlined in the shop manual (which you should refer to when doing this job).
[ Thanks to Bob Barry for this information ]
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