Mercury - U-Joint Bellows Assembly Sterndrive Driveline Protection 86840A05. Overview. This U-joint bellows is the flexible sleeve that keeps water out of the driveline area on Bravo, Blackhawk, and Vazer drives. When the old one dries out or starts cracking, it doesn't take much for water to find its way in, and that can turn into an expensive mess pretty quickly. Swapping in a fresh OEM bellows is one of those jobs that feels small but makes a big difference. The kit comes with the clamps you