* Worn belt: The most common cause. A worn belt will stretch and slip. The solution is to replace the belt.
* Worn or damaged pulleys: A pulley that's wobbly, seized, or has a damaged groove can cause the belt to ride improperly and slip. Inspect all pulleys carefully for damage. A damaged pulley needs repair or replacement.
* Incorrect routing: The belt must be routed correctly around all the pulleys. A misrouted belt will be improperly tensioned, or may even slip off. Consult a repair manual or online diagram for your specific truck engine to ensure correct routing.
* Tensioner issues: The tensioner pulley is what provides the correct belt tension. On a 1990 Chevy truck, the tensioner likely uses a spring to maintain tension. Problems here could include:
* Broken spring: This will result in a loose belt. The tensioner needs replacement.
* Seized tensioner: This could make the belt too tight, causing premature wear. The tensioner needs replacement or repair (if possible).
How to check and potentially replace a serpentine belt:
1. Identify your engine: Knowing the specific engine (e.g., 4.3L V6, 5.7L V8) is crucial for finding the correct belt and diagrams.
2. Consult a repair manual: A Haynes or Chilton manual for your specific year and model truck is highly recommended. These manuals will have diagrams showing the belt routing and provide step-by-step instructions for replacement.
3. Locate the tensioner: This pulley has a mechanism to adjust the belt tension. It might have a bolt to loosen it, allowing you to adjust the belt. (Again, usually you don't adjust, you replace the belt)
4. Inspect the belt: Look for cracks, fraying, glazing, or excessive wear. If any of these are present, replace the belt.
5. Inspect the pulleys: Look for any damage to the pulleys. Wobbly or damaged pulleys should be repaired or replaced.
6. Belt replacement: If the belt is worn or a pulley is damaged, you'll need to replace the belt and/or the damaged component(s). This usually involves loosening the tensioner (following your repair manual's instructions carefully), removing the old belt, and installing the new one in the correct routing. Make sure the new belt is the correct size and type for your vehicle.
In short: You don't typically adjust a serpentine belt; you replace it if it's worn or if there's a problem with the tensioner or pulleys. Always consult a repair manual for your specific truck model before attempting any repairs. If you're uncomfortable working on your vehicle, take it to a qualified mechanic.
