[SSDiv6]

Originally Posted by Greg Reimer 7376

Seems to me that the 7.5" rear end was a V-6 rear end that came out in the mid '70's when everything got downsized and cheapened to the point of near extinction. The 8.5" rear end came along in the 72 model year in a few cars, it replaced the 8.2" 10 bolt and the 12 bolt, but by '73 or so, nothing made enough horsepower to break it anyway. The 8.5 would probably hold up if you put steel web caps in it, the right hardness gears, of which there are not anywhere near the ratios available that the 12 bolt has to offer, a good spool, proper axles, and by the time you did this, you might as well have bought an aftermarket 12 bolt housing that's right for the car. This is a clear cut case of paying to do it right and paying only once. The Buick GranSport turbo cars had the 8.5, but the turbo cars didn't leave nearly as hard as a small block stocker will, they made up for it with boost down the track a ways.

There are a lot of GM Heavy Stock Eliminator cars running the 8.5 rear end with no problems. Replace the cap bolts with ARP studs, use a solid pinion spacer with shims in lieu of the factory collapsible/crush spacer and put the girdle rear cover and you are good to go.