Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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the 8.5 housing I build off of for early A body's is a '71-72 Old/Buick piece. At the very end of the '72 model year, a few actually made it into a few very late Fremont plant built ElCo's. To install in the place of any 8.2 rear, a type "O", or any 12 bolt, will need to shorten the stock length driveshaft 7/8".
Built from the factory with a posi, the early 8.5 A body rears are next to non existent. Since the early 90's, I've pulled well over four hundred of the early 8.5 A body rears, and only two were factory posi rears, plus another I picked up at '01 Norwalk (seller didnt know what it was). Another issue, is if you do stumble onto a factory 8.5 posi out of a '71, good chance its a cone type Warner Motive posi, and most likely, it will be worn out. I've had '71 original posi 8.5 A body rears in here from Cutlasses and 442's to Stage 1 GS's, and each one had a well warn 2 pinion cone posi. All through the '90's, I rebuilt the S spring 8.5 posi's, shimmed up with new clutch packs. Eventually, the price of the GM clutches more than doubled, then GM discontinued them. Today, there is a limited reproduction of the clutches, but at $200 a set, (unless one buys 20 sets), it hardly makes sense to rebuild the S spring posi carriers. Just makes a lot more sense to buy a new Eaton posi carrier. Behind something like a moderate performance 389 or 400, can stick with 28 spline carrier and run the stock tapered beating axles. The stock tapered bearing axles actually are quite strong, Having seen where both will twist and break, many of us would put them on par with the forged axles out of the HD Safe-t-track Pontiac rears (only avail with 3.90 and 4.33 HD STT rears). Running quicker than high 11's on slicks in a 3700 lb streetcar, ESP with manual trans, I'll build with new HD 30 spline Eaton carrier and matching axles from Moser or Dutchman. Will even go that route for extra insurance in a 12 sec car. Desiring to go even quicker, into the high tens, footbraked,, will build off an A10 tapered bearing end A body housing and fit a lh steel cap and a higher end spicer 1350 pinion flange.