2. Locate the serpentine belt. On the 1989 GMC Vandura van the serpentine belt is located in the front of the engine bay, running over several pulleys on the front of the engine and the power steering pump.
3. Loosen the belt tensioner. On the 1989 GMC Vandura, this can be done by using a 15 mm wrench to turn the tensioner pulley counterclockwise.
4. Remove the serpentine belt. To do this, you should start by slipping the belt off of the tensioner pulley. Then you should be able to remove the serpentine belt from the other pulleys.
5. Inspect the serpentine belt. While the serpentine belt is removed you should inspect it to make sure that it is not damaged or worn. If the belt is cracked, frayed, or has any other damage it should be replaced.
6. Install the new serpentine belt. If you are installing a new serpentine belt start by installing it onto the tensioner pulley (the last one removed when taking off the old belt). Then continue placing it around the rest of the pulleys in any order you choose until it is properly routed.
7. Tension the serpentine belt. There are several different types of tensioners that can be used on a 1989 GMC Vandura van, if the tensioner uses an adjusting rod with two nuts or a bolt at one end loosen one nut allowing the adjusting rod to move freely, use a 15mm wrench on the other nut to turn it clockwise until the rod moves enough so that the serpentine belt has about a 1/2" deflection (amount it moves up or down) when in the middle pushed with a finger. If the tensioner uses a spring tighten the tensioner pulley and then push it towards the engine by using a breaker bar or large screwdriver through the hole in the tensioner to release it, you should hear a click when it releases indicating it is properly tensioned.
8. Check your work. Start the engine and let it run for a few minutes. Then, turn the engine off and check the tension on the serpentine belt. The belt should be tight, but not too tight. If the belt is too tight, it can cause damage to the engine.
