The 8.5" 10-bolts came in 71-72 Cutlass/442 & 71-72 Skylark/GS. I have "heard" that some 72 Lemans/GTO's had them,but I have always seen the 8.2's in them. There are also 2 different castings for the pumpkins,which may make it a little confusing for someone looking for an 8.5" 10-bolt. There is the style that I have seen under ALL of the 71-72 Buicks,which has a large letter "A" cast onto the top of it,& has a smooth cover with notches at 3:00 & 9:00. This style came under some 71-72 Cutlass/442's,depending on what plant they were built at. The second style came under 71-72 Cutlass/442's built in Lansing,as well as some of the other plants.This style has a large "O" on each side of the pumpkin,frontside,where the axle tube goes into the pumpkin.This has a round cover,with a protruding rib,going from 12:00 to 3:00. Both of these have a 10-bolt cover,with an 8.5" 10-bolt ring gear,bolt-in axles,& a yoke that uses bolts & straps.The aftermarket girdle covers will fit both of these styles. The 8.2" covers will NOT fit these. You should also not get confused with the 12-bolt O-axle.This is Oldsmobiles version of a 12-bolt.They made it from 1967-1970,for the Cutlass/442. It has a smooth 12-bolt cover,with an 8.5" 10-bolt ring gear,& bolt-in axles.This particular rear is unique to itself,as the parts do not interchange with any other type of rear.
Olds 12 bolt info... The axles in a 12 bolt 'O' tpyr rear interchange with all BOP rears 67-70 and pontiac 8.2 1971 & 1972 with 60 degree spline axles and matching the sealed and or oiled tapered bearing axle with the correct housing. 67-68 sealed bearing 69-72 tapered/ internally oiled bearing. Also the yoke from the olds 12 bolt is identical to the Pontiac 8.2 10 bolt. Just some more info for everyone. Jim:3gears:
The 71-72 Cutlass/442 8.5" 10-bolt rears use the same ring & pinion sets as the 71-72 Skylark/GS. This same rear later became known as the 10-bolt corporate,like what is in the Grand Nationals. The 12-bolt O-axle actuall has 4 different axle bearings throughout the different years. 67-69 Cutlass/442 used the RW-507-CR sealed ball-bearing,with the 8594S inner seal. The 68-69 Vistas used an RW-507-G sealed ball-bearing,with an inner seal.This is a goofy bearing,& hard to find,& expensive. The 1970 Cutlass/442 used the SET-9 roller bearing,with the 712146 outer seal. This is the same bearing/seal design as the 71-72 8.5" 10-bolts. The late-69/1970 Vistas used a SET-10 roller bearing,with the 9912 outer seal This is also the same bearing/seal design as the 71-72 Vista 10-bolts. The 12-bolt O-axle shafts will interchange with some of the 8.2's,but they need to have the same bearing design.The 64-65 8.2" BOP rears were also 5/8" narrower on each side,so you can only use one of the narrower shafts from one of those types of rears. In 71,when they started making the 8.5" 10-bolt,they changed the pitch on teh axle splines.Just enough to confuse some people.They also changed the metal composition,which made a harder axle,& a little less prone to twisting & breakage,so they can hold-up to a little more abuse.
So then most Pontiac GTO's had the 10 bolt 8.2 rears even 71 and 72? Would this be the same 8.2 rear as the pre 71 GS?
Yes the Buick 8.2 will use the same axles and the Pontiac 8.2 10 bolt rears in the same years. 10 bolt Buick 1968-1970 10 bolt Pontiac 1967-1972 67 68 usually sealed bearing axle seal in the tube / 69 70 71 72 A9 tapered axle seal on the axle shaft bearing set-up 60 degree spline so those axle shaft are interchangeable as long as you keep sealed with sealed and tapered with tapered bearing housing etc. The Pontiac 10 bolt 8.2 only changed the ring gear bolt from 3/8 24 thread right hand bolts 64-68 ish and went to 7/16 20 thread count left hand thread from 1968 late to 1972 and beyond into the 10 bolt 8.5 7.5 etc. This was followed with BUICK and 12 bolt olds doing the same 7/6" left hand thread bolt being used also. Some early 12 bolt olds had right hand thread 7 /16" bolts so pay attention to the bolt head and look for the 'L' for left hand thread and sometimes might NOT BE LABELED too. BE careful. You have to watch the pontiac gears as the 7/16" 20 thread posi carriers can only be used with 7/16" gear set...all after market Pontiac 8.2 gears use 3/8" 245 right hand thread. ZOOM use to sell shouldered ring gear bolts to over come this change years ago... To the first question Since all these Muscle cars have been around for at least 40 + years it is always best to ID the rear and NOT go for just a year of the CAR IT IS IN as this will lead to trouble if you are looking for a specific rear. Be equipped with all the info and some reference pictures so that will help you go home with what you want and need. Jim 10 bolt 8.5 is 10 bolt 8.5 corp it is all the same. all gear interchangeable (excluding ABS system being used) All 8.5 rears will use 4 bolts and 2 strap yoke system and a 1 1/4" nut holding the pinion on the pinion. IF you are talking about a A-body 72 and early rear the 8.5 WILL ALWAYS BE BOLT IN AXLE PERIOD! So these few little exacts (ALL 3 of these facts MUST BE PRESENT or pass it by) will and should help you get the correct rear. ALL Pontiac rears used u-bolts...
I believe the universal joint is different in the chevy. If you have the original 8.5 ten bolt from the Skylark, it is preferable as it equipped with bolt in axles.
There are NO 10 bolt 8.5 from 1965-1972 in a chevelle FACTORY. Someone could have transplanted one from years ago if they blew the rear up. The buick / olds 10 bolt 8.5 will bolt into a 1968-1972 chevelle BUT you will need to shorten the drive shaft from 3/4"-1" and change the u-joint with a 672 precision conversion u-joint. This rear olds and buick 8.5 10 bolt will have bolt in axle retention. A Chevelle 10 bolt will be a 8.2 and have c-clip axle retention. It will bolt into any buick 1971 1972 but you may need to get a longer drive shaft by 3/4"- 1" and the u-joint swap too. The 10 bolt 8.5 was used in the chevelle in 1973 1974 then in the malibu classic 1975-1977. These 10 bolt 8.5 rears are NOT the same as the pre 72 chevelle a-body rears. Different mounting point all together. Hope this answers the questions. Jim
No pontiac a-bodys had 8.5s in them from GM...pontiac thought the 8.2 was strong enough...if it had a 455 in 70-72 it got the chevelle 12 bolt.. chevelles didnt get them either..but the 8.2 in a chevelle looks like an 8.5...it'll fool ya, if all ya look at it the inspection cover...there are no steps on the bottom of the housing.... heres a 71 buick 8.5 on the top..see the steps on the lower housing...under it is a chevelle 8.2 out of a 71...NO STEPS...but smooth cover.. heres a 71 Nova 8.5...smooth cover,but has the steps..i think this is where people get confused heres a 71 chevelle 8.2...smooth cover, but no steps
Brian I saw your posts on GM rear ends. Would you be able to tell me if a 1967 GTO complete posi rear (Drum to Drum) will fit in my 1969 Buick GS 400. Would appreciate any help or direction. Thanx Mike
I know it's been months and hopefully by now you got your answer mkeeler, but, I don't see any post so here is my response. It will fit bit it is narrower than the 68-72 rear so you will be able to fit larger tires in your wheel wells! But, it will be the weaker 10 bolt design that we are looking to replace with the 8.5 rear. Also the control arms are different length if I remember so use the arms from your car.
The A-casting should have bolt-in axles. The codes jive with a 71-72 Skylark/GS 8.5” 10-bolt. Do you have any pictures of this?
All the early Buick rears were bolt in axle. From 64-67, there were the BOP 8.2 10 bolts, and from 68-70, the BUICK ONLY 8.2 10 bolt. In 71-72 Skylark/GS and Olds Cutlass got the Corporate center section 8.5, and they were bolt in axle. Later rears in the 73 and up A body were 8.5 C clip rears as were the Grand National rears. As far as I know, those C clip rears will not directly bolt in to earlier A bodies without modification. In a 50 year old car, lots of parts get changed, so unless you have owned this 1970 Skylark from new, someone could have put a different rear in it. Some Canadian built Skylarks got the Chevy 12 bolt which was a C clip rear.
Pics are in another thread started https://v8buick.com/index.php?threads/identify-buick-rear.369869/#post-3210198
