Hi range has the plunger rod in the actuator pulled up and gravity wants to pull it down. That's why you never park in HI range, is something bumps the truck the plunger could fall half way putting the rear in neutral allowing the truck to roll free.
Take the diaphragm and plates out, cut a length of tubing to fit over the plunger rod and put the two plates back on the rod...just make sure the tubing is at the correct length to have the rear fully in HI range. Put the cap back on and plug the vacuum ports to keep dirt out.
Mike B
