I have a 71 supreme that has a 8.5 rear with 2.56 open carrier (28 spline) and I am looking for to get a posi carrier with 3.55 or 3.73 ratio. I looked but couldn't find anything legible on the stamping, is this considered a "corporate rear" that a chevy 8.5 carrier and ring/pinion will fit?

 

No thats not a corprate rear. Its an "O" style rear.

Your current carrier is probably the 673. Its for 2.56 and 2.78.

In order to install..say a 3:42 or up, you would need the 588 carrier.

FYI..if you come across the 672 carrier, thats for 31 splines...just in case it comes across your radar.

I don't think you can put a 3.55 or 3.73 on the O style without a spacer or some kind of machining=fabrication.

Lets see what some of the guys that really know, have to say about it.

Edit..You did'nt mention this but I will, If you come across the 671 carrier this one would allow you to use 3.08 or 3.23.

 

Any idea if anyone sells aftermarket carriers that will work or am I going to have to find a old carrier or a complete rear to swap? Thanks for the info, this is my first real foray into a Olds restoration.

 

if it is an original 71 Cutlass rearend it will have an 8.5" with 10 bolts on cover and 10 bolts on the ring gear, you can use the following as a direct bolt-in with 28 spline axles:

Eaton 19557-010
Auburn 542018
Auburn Pro 542050
Detroit True Trac 912A556

I personally would use the Eaton or the True Trac also, you will be able to use the gear ratios you mentioned

 

This is the 67-70 Type "O" 12 bolt which has 12 bolts at the cover and 10 bolts at the ring gear and to clearify these gears or carriers will not interchange with the 71 and newer 8.5" 10 bolt ....

 

Alright, thank you for the info.

 

If your 71 Supreme has the original rearend,then it should be the 8.5" 10-bolt.This later became known as the 8.5" corporate.It should have a 10-bolt cover,8.5" 10-bolt ring gear,28-spline axles,and 30-spline pinion.Parts for these are plentiful.They do not make a 3:55 gear for them though.They make a 3:42,then it jumps to 3:73.
1970 was the last year for the O-type rear,so your car does not have one of those,unless someone swapped one in there in the past.

 

I had a minute to go out and look at the rear again. It does have 28 spline axles but I didn't have time to look at the pinion. I did notice that the axle did not have c clips. Will that help differentiate between a corporate and type O?


Heres a pic of before I tore it apart.

 

That is an 8.5" 10-bolt.That is what I call the A-casting.If you look on top of the pumpkin,you will find a large letter "A",and there is also an "A" on each side,where the tubes go into the pumpkin.If it's grimed-up & dirty,you may not see these,but I call tell from your picture that is what you have.There are plenty of parts available for these,and they are a great rear to build.

 

Plenty of parts, correct me if I'm wrong but that'd make it a "corporate" rear that a Chevy carrier would work? Sorry for being redundant but I am still alittle confused.

 

They began making this rear in 1971,and it later became known as the 8.5" corporate,or the 10-bolt corporate.GM put these under a variety of cars & trucks in the 70's,80's,90's,2000's. The only thing they changed is in 1988,they changed the axle spline count from 28 to 30.
The newer,aftermarket posi units have a larger bearing hub,but there are bearings available to install them into the older rears.The smaller hubs used the LM501349 bearing & LM501314 race. The newer larger hubs use the LM102949 bearing,and LM102911 race.
The pinion bearings are the same for all of them: M802048 bearing(inner),M802011 race(inner),M88048 bearing(outer),M88010 race(outer),and the #2043 seal.
Your axles are bolt-in,no c-clips,and the axle bearings are # SET9 or also called A9,and axle seal # 712146.

 

Amazing info. Thank you for the assistance.

 

Will the Eaton 19557-010 mentioned above for these 8.5 rearends work with bolt on axles too? I see the c clip designation mentioned out there in the specs on the web... but no mention of the bolt on axles fitment with the 19557. Ive be assuming yes. Just want to be sure. Thx.

 

Yes it will.

 

Thx Brian