Need advice please. 2003 Quadcab with 5.9, 178,000 miles. Standing next to my truck today and heard a weird sound, kinda like a thumping. Popped the hood and noticed the serpentine belt thumping, kinda like a guitar string being plucked. No squealing or burning. Turned air conditioner off and it quit. Turned it on off 2 more times and duplicated it. When on, A/C blows cold doesn't miss a lick. A/C on = noise/Thumping, A/C off = no noise/thumping. So, is it the A/C compressor clutch about to seize or the belt tensioner pulley about to give it up ? Or something else all together?

Thanks,

TXPower

 

Can't say for sure what the problem is. Have you ever changed the tensioner? A few years ago the belt on my truck shred one of the outside "ribs". Not sure what to call it, but one of the "V's" (ribs) got torn off. Changed the belt and it happened again very quickly. Removed the alternator and checked the bearings, but they were OK. The water pump was dripping, so changed that. Removed the tensioner and it was badly worn, but worn sort of oval and not round. No idea how that could happen. If yours is worn like mine, it could maybe cause a thumping noise. Installed a new one and as much as possible checked everything else for alignment. Installed another new belt and once again the outside rib vanished. As everything was working fine, decided to leave the damaged belt on, but carried a spare. Must have about 50,000 miles on the damaged belt and other than a frayed edge, it looks just fine.

 

Also, probably not your problem but there was a bulliten on the alternator bracket for 03's. The stamped bracket could crack, and the uptdated bracket is cast.

Anyway, if it were mine I think I'd pull the belt and check the tensioner over carefully (or just replace it) and rotate the alternator, AC compressor and whatever else and make sure none have a rough bearing going out feel.

Do you have a Jake? The vacuum pump they use has been known to fail.