His truck is equipped with manually locking hubs already in addition to the automatic system. The manual lock is just a backup in case the auto system fails.Chipper;1230305 said:Just change the lockout hubs to manual type from Warn or Milemarker. I wouldn't waste any time trying to trouble shoot for a vacuum leak. Couple hundred bucks or less and a hours labor. Then you will NEVER have to worry about them again.............. Best part is you will KNOW that the hubs are locked or unlocked and not hanging up wearing out your front end and wasting fuel.