well one possible reason, when you stomp on the gas the pinion gear attempts to climb up the ring gear. when this happens, the nose of the rear end tries to pinion up. when this happens it can shock the heim joins of the ladder bars hard enough to shear them. if the tires dont break loose before you reach failure, or if the joints are brittle or made to the incorrect spec. then this happens. had a friend's 72 nova big block do this when he had 12.5" slicks and a 400 shot of nitrous, at the line he was at peak torque and it gave him about the equivalent of a 250 shot when he came off the transbrake, it was only supposed to deliver a 150 off the line. live and learn.