I broke one once. it was out of a 73 Duster 340 car with near 100,000 miles on it, installed in a 35 Dodge 2 door sedan with my 150lbs son sitting directly above the rear end. It was a "limited slip" 3:55 gear rear.

It was a fairly cool Sunday morning, we were heading to a car show. I was having issues with the carb. The stupid thing would cough and die every time I was trying to get through a stop sign on a busy street. After about the 4th attempt, I put the car in neutral, revved it to about 2500, and shifted it it into drive. Away it went, for about 2 feet before the bang and the sound of breaking gear teeth joined with the car no longer moving under power. Lets say we didn't make it to the car show that day.

One of the two bolts that holds the carrier bearing cap on one side broke off even with the housing and allowed the carrier to get cocked. That action stripped off about 6 teeth from the ring gear, and most of the teeth from the pinion gear. I replaced the 8 1/4 with a 9 1/4 I had in my pile of parts.

The odds are about even that if my son wasn't sitting directly above the rear end, the tires would have spun and the rear probably would have survived. It is also possible that the failed bolt was already cracked from previous abuse. I bought the Dusted used, and beat the crap out of it, then I beat the crap out of the sedan before the axle failure. The axle failure didn't change my driving habits, I was pretty used to accumulating broken parts.

How tough that 8 1/4 is depends on how bad you plan on treating it. My broken 8 1/4 went 100,000 miles on the street (and the strip at least a few times) before it got to me and then was in the sedan at least 3 years before I broke it with the neutral drop.