motoring along at a steady 35, THUNK!!! on the bed floor; THUMPTHUMPTHUMP immediately thereafter. I first thought blowout, but it still still steered and rolled fine. Pulled over and shut down. Took a look underneath and saw that the rear u-joint had tossed a cap and started to shake like mad. No big deal, easy fix. It could have been more eventful, but I wasn't going very fast when the snap ring apparently failed.