The internal diaphragm on certain Ford and Lincoln vacuum-activated hub actuators is highly failure-prone. This patented Dorman OE FIX replacement restores 4WD while eliminating the problematic original functions for greater reliability. With over 80 .000 products backed by a team of product engineers and experts based in the United States . Dorman is the first choice of automotive professionals . backyard mechanics . and do-it-yourselfers all over North America.