Hi looking for some help and information, I have 1973 Buick Century Luxus with a 10 bolt 8.5 2.73 gears when they went to install a new Yukon posi unit and 3.42 gears they found that it had the bolt in axles not C clip....I was told there was no such thing.......... and yet I've seen the odd thing written about rare instances of 8.5 with bolt in.......... anyway the posi unit and gears didn't fit and they don't know why or what would work. Anyone out there have any ideas or knowledge of such a beast? Thanks.
Yes my 75 is bolt in. I have owned mostly 73 - 77 regal/Century's and all were the same. I can't say 100% for sure, but I think the c clips are mostly chevy.
I have never had any issue with gears not fitting.......just buy corporate 8 5 gears and they should fit.........all mi e have been from 71/72. all had bolt in axles even used fears from my older bolt in axles on a chevy c clip so if the ordered 8.5 gears they should fit. I think the posi where different, but I dont see why if you had a carrier ment for c clip why your bolt in axles wouldnt fit...but I know you cant go the other way. did they get a carrier for 30 spline truck?? they had 8.5 too but where different
I will check about about the different carrier for a truck ...... you never know, that just might be what happened. Thanks
Bolt in axles are superior to c-clips. Be glad you have them. The stock 28 spline bolt in axles are good into the 12s, possibly 11s . You need to determine how many splines your posi accepts and what series it is. 2 or 3 series ? Talk with either Brian Trick or Monza (JD Race) . They are both members of the board. Jim
A 408 GM Posi and GM 8.5/8.6 gears will fit just fine, there are also Yukon posis that will work too - Suggest PM Monzas (JD Race), Everyday performance or Brian Trick to get the proper applications. You might have a 70-71 Chev 8.2 application on your hands...
According to my Buick service manual, Skylarks/GS 71-72 usually got B rear ends (Buick, for example LSB, LWB, LHB). Whereas many of the other Buicks like Electra, Riveria got Oldsmobile rear ends (QEO, QHO). These B-O differentials have the bolt-in axles. Whereas the C-K axles have the c-clips, which was found in some Le Sabres. Never know what you get under a Buick. Not sure what they did in the following years, but an 8.5 with bolt-in axles is about as good as it gets for a 10-bolt.
All of the new 8.5” posi units are machined for c-clips,but will fit all bolt-in axle applications as well. The original GM 410408N posi unit is the same way. It is machined for c-clips,but will work with bolt-in axles. The side gears inside the units have a circle/pocket machined in them to accept c-clips. The axle spline and cut/pitch of the splines are the same for all of the 8.5” 28-spline shafts. What posi unit and what gears did you try to install?
All axles including and after 1971 were 45 degree spline for GM and as Brian stated bolt in or c-clip posi units will work with bolt in axles. so all 410408 410409 725 and 726 castings will ALL work in the 10 bol t 8.5 BOLT IN AXLE rears from 1971 - 1976 era... You have to also remember that the spider gears and the carrier case can only handle so much torque and flex before failing too. so even if you get better axles you will only keep finding another weak link... So pick what is least expensive to replace and cross your fingers. Jim JD
Sooooo What did you have for a rear end size? There is only 10 bolt 8.5 or the weird few that came with the 8.75 in the a-bodys which were suppose to be the 12 bolt ring upgrade heavy duty rear 10 bolt cover that looks like a Pontiac 8.2 cover but physically larger in diameter. . Or did you just have the incompetent installers... as it usually is. 50 -60% of my business is fixing other shops messes because they were suppose to be the professional expert mechanic...lol. WHAT DOES THAT ONE COMMERCIAL SAY... Hey, stay in your lane BUD....lol In other words stick to what you know. Jim JD
