How To Replace A Serpentine Drive Belt

Serpentine belts will last about 150,000 miles unlike the older V-belts which wore out around 40 or 50,000 miles. Serpentine belts usually give you plenty of warning before they fail totally unlike the V-belt, which might not give you any warning before breaking. Serpentine belts start to squeal way before they are at the point of failing. When they start squealing it is time to replace them. Of course, the belt may not be failing; a seized up tensioner or idler will cause the belt to squeal, as will pulleys that are out of alignment.

Tools And Supplies
Service manual with belt routing diagram
New serpentine belt
3/8 inch drive ratchet
3/8 inch extension bar
24 inch metal straight edge
Dial indicator with magnetic base

Inspect Before Replacing
Check the wear pattern before removing and discarding the old belt. Normal wear occurs on the belt ribs. Looks for cracks’ running across the belt’s ribbed surface indicating a normal wear pattern. Look for damage to the belt edges indicating an abnormal wear pattern. Look for rubber banding or exposed tufts of fiberglass reinforcement indicating that other serious problems exist. Damage to the belt edges indicates a problem with one or more of the pulleys or a problem with an idler or tensioner. You should locate and correct any problems with a pulley, idler, or tensioner before installing the new belt. Depending on what the problem is, not fixing it could lead to more serious damage to the engine and its accessory components.

Check To See That All Pulleys Are Coplanar And Square
If the term "coplanar" is unfamiliar, it comes from geometry and means "lying in the same plane." To check to see if all the pulleys are coplanar all you need is metal straight edge that is "true." Lay the straightedge across any two pulleys and it should make contact with the pulleys edges. If it makes contact with one edge but not the other, the pulleys are not coplanar, and you need to correct that problem. The easiest way to check to see if a pulley is square is with a dial indicator.

You need to replace idler pulleys and tensioners with worn bearings because they will be out of square. A bent accessory-mounting bracket could cause accessory pulleys to be out of square. A bent bracket can be straightened but you are better off replacing the bracket. You can pick one up at a salvage yard for a couple of bucks and save yourself hours of frustrating trial and error work.

Inspect the area for oil and other fluid leaks
You must locate and repair any oil and power steering fluid leaks before installing a new belt. Any fluids, even antifreeze will cause a serpentine belt to slip because the smooth side of the belt drives some accessories. Replace or have replaced any leaking oil seals, gaskets, or accessories such as power steering pumps or water pumps.

Remove And Replace
Back in the day when the V-belt was omnipresent, the mechanic needed three hands to replace a single belt, or so it seemed. We needed to hold the alternator in just right position with one hand while tightening the hold down bolt with the other hand, which was not always an easy task. How many times did we tighten that hold down bolts not quite all the way and then pry on the alternator to get the belt tension just, right? Prying against the alternator’s case was not good for the alternator, but we did it. For once, the engineers were thinking about those who have to repair the cars they design. All you need to remove and replace a serpentine drive belt is a 3/8-inch drive ratchet and a short extension bar. The engineers placed a square hole in the tensioner that the end of a 3/8-inch drive extension bar fits perfectly, allowing you to use a 3/8-inch drive ratchet or breaker bar to pivot the tensioner away from the belt.

Double Check The Belts Routing
Check and recheck the path the new serpentine belt is taking around the various pulleys. With its serpentine path, it is very easy to get it wrong and having an a/c compressor, water pump, or power steering pump run backwards is not a good thing. Check the hash mark on the tensioner, it should be in the center of the notch. The two sides of the notch represent the upper and lower tension limits.

The engine compartments of modern cars are very crowded and we often have to remove components to get to the part we need to work on. You may have removed the radiator reservoir tank or some other component to get access to the serpentine belt, so be sure to replace everything.