Introduction: How to Replace a Serpentine Belt

By 4DIYers
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Video tutorial on how to replace a serpentine belt on a vehicle. A serpentine belt is a wide thin style belt with multiple ridges that drives multiple components such as the alternator, water pump, power steering pump, and ac compressor. As for maintenance intervals, this will depend on the vehicle’s manufacturer. Manufacturers recommend to inspect the belts at every 32,000km or 20,000 miles to 160,000km or 100,000 miles and then replaced accordingly if you see any cracking, pieces missing, fraying, glazing, etc. Normally when I’m ever under the hood, such as during an oil change, it should be inspected. If the belt were to fail, as in breaking, sometimes they might just fall off or it can damage other engine components in the process. This particular vehicle I am working with here today is a 1997 BMW 540i.

Tools/Supplies Needed:

  • ratchet and socket set
  • torque wrench
  • new replacement belt
  • new tensioner
  • new pulley
  • wrench set
  • jack and axle stands or ramps

Step 1:

Start by locating the tensioner mechanism. For this model I am able to pull the tensioner pulley back, and then lock it into place by tightening back up a bolt which also maintains the tension once set. Loosen the 13mm pivot point bolt and then the 13mm bolt which locks the slotted adjustment bracket. Use a 17mm wrench to pull the tension back, then tighten the 13mm bolt which locks the slotted portion in the bracket. Remove the belt, this can be tricky if you are working with an inline drivetrain that is equipped with a mechanical fan. When removing the belt, make note of it’s position as they can only fit on in one way and at times can be routed in a complicated way. Sometimes it helps to take photos, draw a diagram or find a photo online. It’s easiest to remove the belt from the pulleys which ride on the backside first as the ribbed side needs more room to be disengaged from the pulleys.

Step 2:

As you can see the old belt is cracked and is required to be replaced in order to maintain reliability and safety. Pair up the old and new belt to ensure they are the same size.

Step 3:

As for the tensioner replacement, remove the cap on the pivoting pulley using a standard screwdriver, then remove the 13mm bolt. The tensioner is removed back taking off the two 13mm fasteners. Pair up the old and new tensioner to ensure they are correct. Install the new tensioner mechanism and then install it back onto the engine.

Step 4:

We can’t install the other belt as of yet, because the ac compressor belt also needs to be removed. The tension for this must be accessed from the underside of the vehicle. Same basic principle, loosen the 13mm bolt, then the 10mm for the slotted bracket, pull back the tension, and lock the 10mm bolt again. Remove the belt, for this I am also replacing the pulley as the bearing is slightly noisy too. After the pulley has been replaced, again pair up the old and new belt, then install. Ensure it is routed in the proper orientation, install it on the ribbed pulleys first and then on the smooth idler or tensioner pulleys afterwards. Over the longest span between two pulleys, when pushing the serpentine belt in from the smooth side, it should only flex about a 1/2”. Install the final outer belt. Finally tighten the belt to the proper specifications.

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