7 3/4" and 8 1/4" rear weaknesses? (and other ?'s)
7-1/4" rear weakness comes from the small size of the gears, the 7-1/4" ring gear means an proportionately small pinion gear, and tiny little side gears and planetary gears, these are the weak spot, they are so small it doesn't take much abuse to break them, they are fine for normal driving, but if you put any hard loads on them, (like hard launches) they just break, a 7-1/4" with sure grip is stronger only because the sure grip splits the load between both side gears, so each side only takes half as much abuse, with the other side taking the other half, resulting in a stronger longer lasting rear,
8-1/4" rears do not suffer from these problems, there only weakness is due to how the axles are retained, 8-1/4" rears use C-clips to hold the axles in (like a ford 8.8 rear in a fox body mustang) the bad rep that the 8-1/4 got is not due to it being a BAD rear (its actually a very good rear), but rather from MOPAR deciding to use it to replace the superior and venerable 8-3/4"