How To Replace the Serpentine Belt

We’ll be replacing the serpentine belt on a 1989 Chevrolet Silverado. The idler pulley broke at the same time as the serpentine. The idler breaking may have been the reason for the serpentine breaking as well.

The serpentine belt is that long belt on an engine that winds itself around the pulleys of several engine components such as the crankshaft pulley, power steering pulley, the coolant pump pulley, the a/c compressor pulley (if the vehicle is equipped with a/c), the belt tensioner pulley and idler pulley. This is the list of components on the Chevrolet we worked on, yours may differ. The components involved vary according to the vehicle type and the components used on the engine. Your vehicles particular routing of the serpentine belt can be found under the hood on a sticker or in your automotive manual.

If the belt fails for what ever reason, the engine won’t necessarily shut off (unless the serpentine belt gets caught up on the crankshaft and forces it to shut down), but you will usually hear a loud bang when it snaps and vital power assistance will immediately end. The power steering will stop and it will suddenly be very, very difficult to steer. The power braking will stop just as fast as the power steering, and it will be difficult to stop the vehicle. The engine will begin to overheat FAST because the water pump no longer turns the coolant for the engine. As you can see the serpentine belt runs the entire engine.

One hot summer day this 1989 Chevrolet was towing a trailer, up a steep hill, and suddenly a bang came from the engine and the vehicle started overheating super fast. The driver could barely turn the steering wheel to get off the roadway. The photo below is what the serpentine belt looked like once it was untangled from the engine:

1989 Chevrolet Serpentine Belt

The idler pulley had melted and ripped off as well. The .gif below is the idler pulley:

The first thing we needed to do was replace that idler pulley. There is an after market pulley that is made of steel. Steel will be more reliable than the plastic one that melted. The steel idler pulley ran about $30 (as of 2018).

WOW! This one’s only $19! I paid $30!

We also picked up a new serpentine belt obviously. If your belt doesn’t rip off or break like this one did a good rule of thumb for replacement is when you can see cracks along the grooved side of the belt OR when the belt has been in use for between 80,000 – 100,000 miles.

Replacing the Serpentine Belt


Make a hand written note, or take a picture, of the routing of the serpentine belt before you do anything! The Chevrolet we were working on did not have the belt on when we got it, so we looked up the belt routing for its particular engine in the service manual.

If the serpentine belt on your vehicle wasn’t ripped off, like on this Chevrolet truck, you will have to remove it first. This is a very easy process. Using a breaker bar and a socket (Usually a 5/8 socket), put the socket on the tensioner nut and leverage the tensioner in the appropriate direction. It is usually in an upward direction. If the direction you leverage appears to be pressing harder on the belt than leverage the other direction until the belt becomes relaxed. Continue holding the leverage on the tensioner and have someone slip the belt off of any easy to reach pulley, then slowly lower the tensioner, releasing the tension without the belt in place anymore will allow the tensioner to go further down than when you started, this is normal. This is a spring loaded tensioner on this truck. Yours may be hydraulic or electric. Investigate which one it is to use it appropriately.

Now that the belt is off of the pulley or pulleys, un-route it from the engine. Nothing should need to be removed to get the serpentine belt out. It is one solid piece routed around components.

After the serpentine belt was removed the idler pulley was dangling from its mount so it was removed. The new steel idler pulley was set up and installed.

Once the idler pulley is back on it’s time to put the serpentine belt on. Take the serpentine belt and slide one side of the serpentine belt past the engine fan and loop it under the crankshaft. Work your way up and around each component as you come to it according to the picture you drew of the routing or the photo you took. Sometimes what appears to be the back side of the belt (the smooth side) will be the side that comes into contact with some of the pulleys. One example is the idler pulley and the tensioner pulley. These pulleys are both smooth, and the smooth side of the belt will be the side to contact these pulleys. And the grooved side will come into contact with the grooved pulleys. Pretty simple stuff here.

When you get the serpentine belt up and over and around its proper engine components you will need to use the breaker bar and socket to put leverage on the tensioner pulley nut again. Two people work better than one on this endeavor.

Attach the breaker bar and socket to the socket on the front of the tensioner pulley, apply leverage (use them muscles!) and have your assistant slip the belt over the pulley while you hold the pulley up out of the way with your breaker bar and socket. Slowly lower the tensioner pulley once your assistant is out of the way.

That is it!! Your done. Double check the serpentine belt routing and if it all looks good, fire it up and check that everything is tight and straight.


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