Rearend Woes

[78lemans]

I've got a '78 Pontiac Lemans that originally came with a 3.8 V-6/automatic trans. Currently the car is undergoing a swap to a mildly built (about 300 hp) small-block Chevy/TH350, but I would eventually like to build a 455 Pontiac/TH400 for it.

Thus being the case, I would like to upgrade the stock rearend and wondered what kinds of suggestions you guys might have. I'm pretty poor and this car is getting built pretty slowly, so if there are any relatively cheap junkyard solutions to a stronger rearend, I'm all ears. Bolt-in would be great too, since I don't currently have access to a welder.

I also have a couple questions. A few years ago I looked at an '81 Olds Cutlass wagon with a swapped-in 350/TH350 and 12-bolt posi out of a '69 Chevelle. I had been told previously that the Chevelle 12-bolt would NOT bolt right into a G-body, but the guy with the wagon claimed it was. Who is right?

Other than a 12-bolt, an 8.2 out of a 442 or GN, or one of the ready to bolt in aftermarket 9" rears that's out of my price range, what else could I do? I'm not as concerned with my 7 1/2" holding up under my SBC, but under a beefed-up 455? Thanks guys! -Marc.

 

[mrapii]

12-bolts will not bolt in without special control arms. The rear ends out of Buick GNs and Hurst Olds/442's are 8.5" 10-bolts not an 8.2" which is completely different. The best way to upgrade is with an 8.5" 10-bolt. They're not real plentiful but they are available. In the last month I've seen 3 of them advertised for sale locally and I bought one for $500 out of a 1986 GN, 3.42" Posi in ready to use condition; just shorten the driveshaft by 1". The 8.5" 10-bolts are strong (the 12 bolts have a ring gear only 1/4" larger) and will easily handle your engine. Ford 9" and Strange S-60s are nice but expect to spend upwards of $1500.

 

[ChevyIIMan]

Yeah a 10 bolt 8.5 is the way to go. tore a spring perch off of mine, so $100 for an empty housing, a 30 splie eaton posi and Moser S/S axels, welded the tubes and braced the perches and its good to go.

 

[78lemans]

Thanks guys. I'll keep my eye out for an 8.5 10-bolt then! Is there any easy way to identify one in a junked G-body? Were they available in anything other than a 442 or a GN? Thanks again! -Marc.

 

[mrapii]

At the bottom of the 7.5" there are two "fangs"; the 8.5" has squared-off
extensions where the "fangs" are on a 7.5". The G-Body Hurst Olds also had the 8.5" but you're not going to find any in a wrecking yard. Check local ads or put a wanna-buy ad in your local "Buy&Sell". Try to find one with a Posi, they were optional but fairly common on the GNs and Olds 442/Hurst. Good Hunting!