#1  
Old 07-29-2020, 01:59 PM
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Default Rear diff. ID

Can anyone tell me what diff. this is? GM 67 and up 10 bolt 8.5? Its in a 66 GTO I picked up.
thanks
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  #2  
Old 07-29-2020, 02:11 PM
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That would be my 1st guess, as it is designed for a A-Body vehicle vs a leaf spring car and for sure not a typical Pontiac 10 bolt configuration.

The 8.5 rear axle seems to be a lot better rear axle vs the old 10 bolt Pontiac A-Body parts.

Tom V.

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Old 07-29-2020, 02:31 PM
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On front right hand axle tube, viewed from rear,should be a code. Usually 2 letters.

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Old 07-29-2020, 02:34 PM
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I'm pretty sure that's a 8.2 Chevy "C" clip rear.

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Old 07-29-2020, 03:00 PM
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I'll be taking it out in a few days and take a better look for any markings on it.
I didn't see any that matched it online figured somebody would know.
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Old 07-29-2020, 03:09 PM
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looks like an 8.2 to me

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Old 07-29-2020, 04:07 PM
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The rear cover does look like a Chevy diff cover.
Without the code though it is a 50/50 on being a 8.2 or 8.5 10 bolt rear
cause I know little about 10 bolt chevy rears.
The only 12 bolt A-Body rear did not last long in my GTO.
Post up the code.

Tom V.

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Old 07-29-2020, 07:40 PM
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I don't think the 8.5" GM came out until 1971.

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Old 07-29-2020, 07:54 PM
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I would agree with that but it could be installed in any 1964-1972 A-Body vehicle.

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Old 07-29-2020, 08:14 PM
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Looks like 8.2" Chevy to me. The 8.5" GM rear has square lugs at the 5:00 and 7:00 location on the bottom of the housing that run parallel to the ground

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Old 07-29-2020, 08:37 PM
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Great, Gary H. I will remember that tip.
Tom V.

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Old 07-29-2020, 08:50 PM
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Thanks guys I just couldnít find that cover online anywhere.

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Old 07-29-2020, 09:09 PM
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This is a ‘71 Cutlass 8.5 that I own. ID’ed by Jim Mitschke at JD race. Looks close, if not identical.
Another good identifier is to look at u-joint retention. 8.2 usually have u bolts holding them in, the 8.5 have straps.
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Old 07-29-2020, 09:24 PM
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Default facts...

-there were a little over ONE MILLION '71-72 8.5 A-body rears installed in 71 & 72 GM divisions cars.
-3 different versions of the 71-72 8.5 A-body rear were built. The differences are due to the center housing design, & whether the housing ends accepted A9 or A10 axle bearings.
- one thing ive noted many times: It's never smart to try & identify a housing by poorly written ID Guides & generalities. How many folks use the term "BOP 8.2"? No such thing, just a long time generalization. From decades of hands on experience, there were Early Buick 8.2's, Early Pontiac 8.2's, LATE Buick 8.2's ('68-70), & LATE Pontiac 8.2's. Bunch of differences over the years.

The above pictured rear is indeed an 8.5 A-body rear. Ive posted a pic of that particular style housing on here before & on BuickV8.com when I used to have time to post on that site. In my housing racks have several of that particular style 8.5 A-body housing (only accepts a round cover). Began building up the '71-72 8.5 A-body rears up in the early 90's, while not as common as the style of 8.5 A-body housing that accepts the scalloped style 8.5 cover, have built up over 3 dozen of the style with the round cover.

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Last edited by 'ol Pinion head; 07-29-2020 at 09:35 PM.
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Old 07-29-2020, 09:41 PM
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I didnít notice the difference in the straps there was no driveshaft but it looks like a strap setup not u bolts. I have a 66 10 bolt 3.55 with an Eaton posi
for it but want to run a taller gear a friend has a 66 12 bolt with 3.08ís. I was considering But maybe this will work. Iíll try to get to it tomorrow.

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Old 07-29-2020, 09:49 PM
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Quote:
Originally Posted by JLuger View Post
I didnít notice the difference in the straps there was no driveshaft but it looks like a strap setup not u bolts. I have a 66 10 bolt 3.55 with an Eaton posi
for it but want to run a taller gear a friend has a 66 12 bolt with 3.08ís. I was considering But maybe this will work. Iíll try to get to it tomorrow.
Neither did I. Just blew past the pictures with that info. My bad.

Thanks OPH for the informative post.

Tom V.

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Old 07-30-2020, 03:23 PM
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Well pulled it looks like 2.73's 41/15 on ring gear. Not sure how that went with the M20 2.52 first gear, sounds gd for the interstate though.
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Old 07-30-2020, 04:17 PM
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2.73 was most common ratio on that particular 8.5 A-body rear.

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