Serpentine Belt and Tensioner

A/C Pulley Bearing Article

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All Hummers built from 1994 and up use a serpentine belt. If the tensioner spring or belt breaks you will be dead in the water. The belt drive is what keeps your alternator, vacuum pump, air conditioner and water pump running. The belt and tensioner are maintenance items and don't last forever. Problems with the belts and pulleys usually identify theirselves with a squeeling noise of a slipping belt, a high pitched whine of a bad pulley bearing or the smell of burning rubber. The tensioner is what keeps the belt tight around all the pulleys. If the tensioner wears out or the spring breaks the belt will slip.

Inspect the belt at every oil change. There is an indicator on the tensioner that shows how much the belt is stretched. The picture shows a perfect reading right in the center.

Look for tears, pinholes, bumps, oil on the belt, cracking and parts of the ribs missing. If you have oil on the belt you have to find the leak. Bumps and pin holes mean you have dirt in the grooves. Check for abrasion on the sides of the belt which means the belt is scraping on a bracket or the side of a mis alligned pulley. Abnormal belt wear can be the result of a pulley bearing going bad. Replace the belt if hairline cracks are seen 1/8" apart all around the belt.

Troubleshooting V-ribbed Belt Noise by Gates

Gates engineers recommend replacing your belt every 4 years. If you have over 50,000 miles on your truck I'd replace the belt. Keep the old belt for an emergency spare. There is a belt routing diagram on a sticker under the hood and in the owners manual. My 98 has one on the battery bracket which I luckily didn't paint over. Make sure that you know how to put the new belt on before you take the old belt off.

Serpentine Belt 6.5 turbo
GM Part# 12555011
Goodyear 6PK 2575
Gates KO 61015

Goodyear also has a new style belt. It's called a Goodyear Gatorback ("the quiet belt"). The packaging sleeve lists: AM General - 6.5L diesel, Chevy - 6.5L diesel and GMC - 6.5L diesel, Mercedes-Benz - 6.0L There are two (2) numbers printed on the front of the sleeve:
4061015 and 6PK2580

To replace a belt just take a 3/8" drive breaker bar or ratchet and stick the square end into the square cutout on the tensioner. Pull the bar back to release the spring tension while you push the belt over the pulley.


The Torx socket is a T55

User Note: I've replaced my fan belt for the 5th time in 56,000 mi. It seems that the standard size belt is a bit too long and after a few thousand miles the tensioner extends to its max. When that happens, it flips over center 180 dg. and the spring can't bring it back around causing constant maximum pressure on the belt. When that happens, it seems to put extreme pressure on the fan pulley on the water pump and it causes the bolt holes in the pulley to fracture and shortly thereafter the outer part of the pulley breaks away from a ring inside of the bolt circle. Its happened three times in my trucks life. I bought a shorter belt this time Gates # K061010. It just fits on the truck if you have a long 1/2" socket handle but after it stretches a little the normal tension marks line up. Hopefully this will keep some spring pressure on the belt and not let the tensioner roll over.