Sierra Bravo U-Joint Assembly 18-6401 Bravo U-Joint Assembly | Sierra 18-6401 Direct replacement yoke assembly for Mercruiser Bravo I, II and III stern drives from 1998-2005. Sierra replacement U-joint assembly For Mercruiser Bravo I, II, and III model stern drives serial number OB664190-up from 1998-2005 Includes O-rings Replaces Mercury 12784A10, 864244A2