So i just got my whole front end fixed up like new, or so i thought. I had no 4x4 for a while beacuse i broke the shift fork which engages it. Everything was out of whack! but now everythings fixed and the whole shazam. But when i put it into 4 wheel now its thunks every 20-30 seconds. Is this because i may not have enough vaccum to keep the shift fork engaged? I see a few people around here with posi locks because the vaccum system in their jeep has failed. Would this solve my problem or am i way off? i need advise