1999 FLD 120 Rear end keeps going

How exactly did it "went"? Need some details or it's just guessing

 

just a couple thoughts.

First the rear axle can handle the torque. Torque is something that needs resistance to be produced, you can have a 1000ft/lbs of torque at the fly wheel avalible and there is a 23:1 reduction going to the rear axle (you can do the math) but if there is little resistance, it will only use what is needed to reduce the need.

Second, what has failed on the rear axle, it seems this is very important to know. Did the carrier itself implode or did the ring/pinion have a failure. This needs to be answered.

Third, I wonder if the complete axle unit was replaced or just the pig. If it was just the pig, then the entire unit needs to be replaced and realigned at a good rear axle shop.