1972 Buick Skylark 8.5" 10-bolt upgrade to 30 spline w/posi

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1972 Buick Skylark 8.5" 10-bolt upgrade to 30 spline w/posi

Post by coffee4matt » Sun Apr 03, 2016 11:43 am

My 20 year son has a bone-stock, one owner 72 Skylark 350 purchased a few months ago w/ 80K orig miles, and put a new CPP stage IV suspension, coilovers and 4 wheel disc brakes on it. It has the original "peg leg"/ open differential, 28 splines and bolt-on axles. After a few one-wheel burnouts w/ the stock engine - remember he's 20 so every standing start is a burnout opp - he recently fried the 44 year old rear end internals. Since we plan to eventually upgrade the power on the existing engine somewhat, we'd like to UPgrade rather than merely return to stock the strength of this 8.5" rear end.

We considered just replacing the rear end w/ a 12 bolt or a 9" rear, and if that ultimately looks simpler/ cheaper than rebuilding/upgrading this seemingly rare stock rear end, we will reconsider that solution instead. But it seems these 8.5" 10-bolts for the 71-72 Skylark/Cutlass are almost as strong as a GM 12 bolt if you upgrade them to 30 spline, and since they are so rare, it would be cool to preserve the original rear end if we can make it stronger, and do so economically...

My questions for Jim:

1. Would it be difficult to find any of the parts needed to upgrade our stock, 28 spline axle 8.5 inch rear to a 30 spline rear end w/ posi traction? Every axle I find online that "almost" fills the bill is either 28 spline, or if it's 30 spline it's a C-clip axle (Chevy). Can you source these axles and all other needed parts & sell them to us?

2. If we shipped you our sandblasted/repainted stock rear housing, and our new 12" rear disc brakes, approx how much would it cost for you to rebuild & assemble it all for us as described above, ready to install? (ignore shipping each way) I assume using the stock rear end means the original drive shaft will still work (correct length/ not 1" too long)?

Thanks for your thoughts...Matt

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Re: 1972 Buick Skylark 8.5" 10-bolt upgrade to 30 spline w/posi

Post by monzaz » Mon Apr 04, 2016 6:29 am

First off - These are NOT rare rear ends. They came under EVERY 71 72 Buickand Cutlass and even some Pontiac Lemans etc I have seen them. There were a lot of these cars built.
Being a corporate 8.5 the parts are everywhere and a large selection of parts and ratios.

So you are correct on your drive shaft issues switching to ANY OTHER rear end other than the stock 10 bolt 8.5 you will need a NEW / longer drive shaft

We can have the 30 spline axles custom made and always do each month for other.

Best to PM us with your email address and will send you out a quote for the job.
axles are in the 370.00 range as Bolt in axles only come in race axle alloy. Best for strength and sanctioned racing classes.
Then you have a Posi - gears- master rebuild kit- axle bearing and seal kit and finally labor for set-up and assembly for all the parts.

We also do carrier 12 bolt Chevy rear ends using MOSER housings which are rear heavy duty.

Jim Mitschke
J D Race
J D Race

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