How to Change an Idler Pulley

by Cassandra Tribe

Most cars now use a serpentine drive belt system which means there is one large drive belt instead of several small belts powering all of your accessories. The idler pulley provides the needed tension to the serpentine belt so it can power your vehicle. The new idler pulley replaces the old style of having a separate tensioner pulley. If your belt keeps loosening or even falling off the pulleys, that is a sign that the bearings in the pulley have failed. Fortunately, you can change an idler pulley easily with only a few basic tools.

Park the car on a level surface, open the hood and remove the negative cable from the battery.

Loosen the tension adjustment bolt with a socket wrench so your serpentine belt can fall slack. The tension adjustment bolt will be in one of two places. If your idler pulley is attached to the front of your alternator, there will be a curved slotted piece of metal on the alternator bracket that is locked in position with the tension adjustment bolt. Loosen the bolt and push the entire alternator toward the center of the engine to loosen the tension on the belt. If your idler pulley is not directly attached to your alternator you can locate it and the bolt you need to loosen by identifying the one (small) pulley in the path of your belt that is not attached to any accessory (like a water pump or crankshaft). The tension adjustment bolt will be holding the bracket that supports the pulley in position to the engine block. Loosen the bolt and push the pulley toward the center of the engine to relieve the tension on the belt. Slide the belt off the idler pulley.

Hold the idler pulley so it cannot turn and loosen the center bolt with a socket wrench. Remove the bolt completely and pull the idler pulley from the engine. Installation is the reverse of removal; however, make sure you torque the center bolt of the idler pulley to 40 lbs. when installing the new pulley.

Tip

  • check Don't take your serpentine belt off all the pulleys in your drive system; just slide it off the idler pulley. This will make it easier to reinstall the belt because you will not have to figure out the (often complicated) path it must travel.

Warning

  • close Never perform any work on the drive belt system of a car with the car's battery still connected. If the battery is connected there is a risk that the engine could start as you turn the drive belt and you could be seriously injured.

Items you will need

About the Author

Cassandra Tribe has worked in the construction field for over 17 years and has experience in a variety of mechanical, scientific, automotive and mathematical forms. She has been writing and editing for over 10 years. Her areas of interest include culture and society, automotive, computers, business, the Internet, science and structural engineering and implementation.