71 cutlass posi unit?

[gumbyssfakee]

hi i have a 71 cutlass 4dr and id like to put in a posi but cant tell if the rear is an 8.2 or 8.5. all of the numbers on the rear have been worn away. how can i find out what i have without these and hopefully without opening the rear. also any sugestions on where to get a good unit in the 400-500 dollar range would b appreciated

[sklbndt]

Check on the front and back of the axle housing on the passenger side. It should be there....I know it seems like it's worn off but mine did as well. Lots of wire brushing and you should reveal a stamped code about 1/4 inch high. If on the rear of the axle housing it will be upside down.

[monzaz]

You can check www.JDRace.com in the rear ID section. The 1971 8.5 has 2 straps and 4 bolts that hold the u-joint in place. The 10 bolt 8.2 has 2 u-bolts and 4 nuts that retain the ujoint in place. That should help

And of course this must have 10 bolts on the cover.
If you have a true olds 8.5 the rear cover will be round and have a passenger side bend /ripple in the upper 2 oclock position . (reference picture)
Some Buick 8.5 were put under the olds rears also which have covers that look almost like the 8.2 covers BUT they do not interchange because the 10 bolt pattern for the cover is slightly different. this cover has 3 and 9 oclock scallops in the cover like most 8.2 rears.

Hope that helps

[tpssonic]

Hi,

I'm new to this forum and I have what I think is an Olds posi diff. Can someone tell me if this is an 8.2 or 8.5? If it is an 8.5, is it as strong as the other (Chevy) 8.5s and are part available? Most 8.5s I see have the "full" tabs at the 5 o'clock and 7 o'clock positions- not the BOP scalloped tabs. Thanks,

Tony

[tpssonic]

monzaz,

So the above pic is of an 8.5? That is what I have. The tabs at the bottom look like those of a BOP 8.2- that is what is confusing to me. Mine is a posi and has had 3.42 gears in it (not original). Being that it has 3.42s (using the driveshaft-turning method), I don't think it could be a 8.2. It has "407296" on the pig near the pinion as well as "CFD" (I think) , a big "CE", a "4" (again, not for sure) and has "C19" on the axle tube. Thanks for any information on this rear as there is very little information on this style of differential in the other GM rear end sites. All of the other sites do not mention this unit.

Is this a strong unit? I will be putting it behind a roller cammed 455 Pontiac in the near future.

[monzaz]

OK- Well let me tell you...A true olds 8.5 rear is a tough id in the junk yard.

The picture supplied is the olds 10 bolt 8.5...AND yes it does look just like a 8.2 chevy rear...lol.

The buick 8.5 will have the scalops in the cover at 9 and 3 oclock and the triangular (normal casting) at 5 and 7 o'clock these casting triagle off the bottom of the housing casting are on every 10 bolt 8.5 all the way to 2008 trucks too. OLDS 71 72 were the only castings that were NOT.

WELL HOW THE HECK CAN i TELL difference?
-1. if the yoke has 2 straps and 4 bolts to hold the u-joint in the yoke
-2. must have bolt in axle 1971 1972 a-body
These are absolutes!!!

8.2 Olds will have U-bolts to hold the u-joint in .
and the axle will also have bolt in axles


If you supply pictures I will id it for you if you still are stuck.

here are some other absolute differences
-10 bolt 8.2 olds will have 27 spline yoke
-10 bolt 8.5 will have 30 spline yoke

10 bolt 8.2 axle shafts are 28 spline 60 degree spline
10 bolt 8.5 axle shafts are 28 spline 45 degree spline and WILL NOT FIT INTO A 8.2 SIDE GEAR UNIT. 8.2 WILL FIT THE 8.5 BUT WILL BE A BIT SLOPPY.

Hope this info helps there is always more to learn and again jdrace.com is all GM rear axle info questions are always welcome. I try to hit as many forums as i can in my free time to help. Jim
chevy 8.2 rears and c-clip axles and never had bolt in axle shafts