Diff pulleys have been a weekness, on some vehicles, mainly 501, 511, and db01r. You have to setup the slipper clutch almost perfect as well as the diff, especially if your going to use a 5.5 motor. When the diff pulley gets hot, it's just a matter of time before it fails. Jumping a buggy and immediately punching the throttle with that hot motor, will cause damage every time, if your clutch is not setup properly.
I've gone through two rear diff pulleys on my db01r and I finally loosened my slipper clutch, and now things are good.
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