Fun71

A rebuild, as in installing new bearings and seals, should be straight forward. Gotta make sure you get the correct axle bearings and seals.

olds 307 and 403

My point is, it is a Chevy rear end that Oldsmobile modified for bolt in axles. Another thing that took any the uniqueness of our cars. Think DRCE big block, looks like Olds on the outside, Chevy inside. The better bolt axles also eventually disappeared as well. Not saying it is bad, cheaper chebby gears, more ratios available and no c clips. Just funny it was always the Chevy designed parts that survived. Not sure why GM used the 7.625" in the later 4th gen Camaro/Firebird, was the Borg/Warner 7.75" a lot better, some argue it was not.

DurasII

Maybe I should of stated upgradeable as I would like to go with posi and deeper gears...what is that process or where can I obtain the info to figure it out from?


Thanks!

monzaz

Yes - You can get 3.42 and 3.90 gears for this 12 bolt OLDS rear which is really 10 bolt ring gear bolt count.
Bearings are available for it (master rebuild kit)
You can get aftermarket Limited slip posi units also 3 series (which holds the aftermarket 3.42 and 3.90 Richmond gears AND the 3.08 and 3.23 stock GM gears.

Axle bearings and seals are also available too.

We have all this stuff on the shelf OM if you want prices.

Jim
J D

monzaz

I am sorry corp 8.5 rear was NOT a Chevy design modified to make the olds 8.5 rear. Bolt in axles were 1970 era rears with oiled bearings... this was already in production ALL BOP rear got these axles from 1970 up to 1976. 8.5 corp rear came from all the differentials produced in the 67-70 era BUICK, OLDSMOBILE, PONTIAC AND CHEVY combined.
if anything it was a Oldsmobile AND Buick designed rear. Chevy was not even using a 8.5 rear in a A body till 1973. CAMARO And firebirds got them in late 1971
GM created a rear that all the divisions could use. It was a stream line of money again...One rear to do everything. They picked the best engineering sizes and pieces that worked to do the job.
8.5 rear pinion is unlike any other GM rear...it is the longest out of all GM rears... it gave more leverage to the pinion and ring engagement as the bearings were spread from each other ...
Chevys 10 bolt 8.125 (AKA8.2 chevy) was the weakest of all rears in the muscle car era. 25 spline pinion was he smallest - 28 spline c-clip axles.
Pinion was 1.438, yokes were very weak.
8.5 has NON of these qualities...8.5 has more to do with the 12 bolt chevy than any 10 bot rear.
The biggest failure on the 8.5 rear was when GM increased the axle splines to 30 in 1990 and they never increase the carrier bearing hub OD...they kept the small 10 bolt carrier bearing and hogged out the carrier ID hub to fit the 30 spline axle in and left not enough hub bearing material to bleed off heat from heavy loads.
We were doing 3-4 of the 1/2 ton 90 -98 trucks a week from sheared hearing hubs. Landscapers and plow trucks were snapping them all THE TIME spinning bearings on the hubs too from the heat... These guys were using the 1/2 ton trucks like 1 tons that did not help a bit either... LOL.

GM finally solved the issue with the 8.625 rear which increased the carrier bearings to 12 bolt Chevy size bearings an redesigned the spider gears also to equal up the pinion spiders with the side gear spiders ...

This rear was good enough to last from 1971 till TODAY! 47year run for a axles is INCREDIBLE! You can take 2018 10 bolt 8.625 ring and pinion and install it in your 1971 Oldsmobile 8.5 rear ...

The rear was such a good rear FORD COPIED it. that is how the 8.8 Ford was made.

I am just here to try to give the most informative info i can... I am not here to hurt feels or make anyone look or feel slighted. NOT my intentions.

I do not try an answer questions in other tech sections like trannies and engines etc. If i did it would be a 'well this is what I tried and it worked answer...' which sometimes is fine if it can help someone with the same issue I went through deal.

Take care all,
Jim
J D

monzaz

QUOTED: Just funny it was always the Chevy designed parts that survived. Not sure why GM used the 7.625" in the later 4th gen Camaro/Firebird, was the Borg/Warner 7.75" a lot better, some argue it was not.[/QUOTE]

7.625 in camaros...I think GM knew the camaro / firebird was going away and the whole car was gonna get a revamp. Engine was too far under the cowl it was fat and heavy just going in the wrong direction....
7.625 or 7.75 does not really matter as both were too small for the HP/ torque the car was putting down with the LS motors. reason for the torsen posi units they did not hold either...

7.75 was bolt in axle design and was from Australia Holden division -
it had a small pinion and spine combo and PARTS were so difficult to get

7.625 at least you can get parts if you needed, there were so many built and it at least had aftermarket support with reasonable cost.

Flip a coin...lol.

Thank goodness we have aftermarket whole rears we can just bolt in now.

no more bolt in axles?
Only reason the BOLT in axles stopped Same reason no more drop out third member design----- TOO MUCH MONEY TO MAKE AND MACHINE AGAIN... AUTOMATION PARTS always makes cheaper to produce a c-clip axle and also the axles wear on the bearing.... soon or latter you would need maintenance... keeps the jobs going...lol. It is just the way the world was going... throw it away and stick in a new one. No pressing on and off bearings etc. Get them in get them out. The worker does not need to be as knowledgeable ... cheaper labor COST for dumber guys/gals right? Lets keep making the world and easier place so we can all be dumb. 2 + 2...OH WAIT I HAVE AN APP FOR THAT!!! LOL

Jim
J D

olds 307 and 403

The whole 7.625" rear turned me off buying a used WS6 Firebird. It was another shame, chebby **** on Pontiac, lower hp and slower than the Camaro, 3rd gen and 4th gen, other than the 89 Anniversary model. Chevy was a jealous child who threw themselves on the floor an **** their pants in a rage, anytime any other division planned on a Corvette killer.

monzaz

LOL... you have to get over this stuff... your pouting over stuff you can not control. It has been that way for years and years. ALL comes down to the almighty dollar.

Adapt and over come.

Jim
J D

DurasII

So chevy 3.73 are not interchangeable with the Olds rear?

Fun71

No, they are not interchangeable with the O-Type rear.

olds 307 and 403

See above is why the 71-72 rear should be called a Chevy rear with bolt in axles. When someone refers to them as an Oldsmobile 8.5" rear, it can be very confusing and not the same as the 67-70 Olds 8.5". Good thing Olds put 12 bolts on the cover or it would take a Keen eye to tell them apart.

DurasII

Sure price on the 342 Posi please!

JohnnyBs68S

Back in '05, I spent just over $2K to rebuild my 2.78 open to a 3.90 posi, which included new aftermarket control arms, frame braces, brakes and lines. Spent about $320 on new tools too (including a 20-ton press) to do it myself, would've spent more than that in labor.