Mopar 8 3/4 Rear End (A-Body) - Questions & Help....
I'm not building a HOT ROD or a 3/4 Mile Racer. Just a Duster with cool stuff on it.
For this application;
If the 7.25 has a Limited Slip in it, then
it is NOT junk.
The 7.25OPEN diff. fails when you peg-leg it, as in spin only one tire. This can overheat the cross-pin and then the spider-gears seize to it and then it eventually blows up, usually just leaving you stranded and walking. Another way it fails is by continually slamming power into it with a clutch; but you don't have one of those. Automatics with lo-stalls are easy on the guts.
And a third way is with big tires, a manual trans again, and a high-compression engine; The constant on-throttle/ off-throttle at mid-rpms eventually wears out the sidegears. You can't get big tires on a Duster until you move the springs inboard and; either narrow the axle, or get custom wheels; AND the 74 340 is a low-compression engine; so...........
Before I would buy a bigger rear end, I would pop the cover, inspect the gears and case, and if in good shape I would probably just put a SureGrip into it with fresh EP oil.
However, if the 8.75 comes in cheaper than a SG for the 7.25 (if you don't have one already), then it makes sense to get the 8.75....... but yur still gonna need a SG for that one too.
The only junk 7.25 is a broken one.
Furthermore, IMO,
IT's NO BIG DEAL to run the sbp 5 on 4 for your application. I wouldn't waste my time/money changing it unless I couldn't find the wheels I wanted in that bolt pattern.
The spare tire argument is a crippling story. Carry a plug kit and a 12v compressor and just drive. I haven' carried a spare in IDK, guessing 30 years. Ok I had a flat exactly once, 3 miles from home. My car has 14x7.5" sbps on the front, and 15x10lbps on the rear. My spare tire well carries a few tools and spare parts.
Just my 2cents.
Oh yeah, about that 7.25.... I ran one behind a hi-compression 340 and a 904 for about 3 years in a 65 Valiant wagon; NO SureGrip lots and lots of peg-legging, I mean it couldn't be helped. That was 1975.
The 904 gave up first,lol..................
