Many of your engines’ critical components are driven by belts. Belts operate in tough conditions such as high heat, high speed and considerable tension. Since rubber is an unpredictable material even under ideal conditions, belt failure is one of the most common causes of breakdown on the road. 

Luckily belts are easy to check, and replacing them at home is relatively easy and inexpensive. We’ll show you how.

Most modern vehicles use one or two V-rib drivebelts that drive the water pump, alternator, air conditioning compressor and other components. While these belts are very reliable, failure usually makes the vehicle undriveable. So, it’s important to make sure your belts are in good shape and tensioned properly. 

How to tell when a drivebelt needs replacing

Belts should be flexible and not shiny, which indicates slippage. Look closely at the belt for signs of cracking. Also check that there are no oil or coolant leaks that can get on the belt.

If you hear a squealing noise like this, especially at start up or when you turn on the AC, you’ve got a slipping belt. This can be caused by something as simple as the belt being too loose, but more likely it is just so old, hardened or contaminated that it will no longer grip properly. 

Most recent vehicles use a spring-loaded tensioner to automatically maintain the correct belt tension. On some older vehicles the tension may need to be manually adjusted. 

To replace most belts all you need to do is pry the spring-loaded tensioner away from the belt and pull the belt out from among the pulleys.  Since the routing of the drivebelt is critical, be sure you have a diagram handy. The diagram is usually on a sticker in the engine compartment. If your vehicle does not have a sticker, make a diagram before taking the old belt off. 

With proper routing confirmed, pry the tensioner again and put the belt into place over the last pulley. Be sure the belt is riding in the center of all the pulleys and not off to one side.

On vehicles with manually adjusted belts, you’ll need to loosen a component, and pivot or slide it to release the belt tension. On this type of belt, you need to pry the component away from the engine, or crank the adjuster bolt, to get the proper tension, then tighten the bolts. The general rule of thumb is to leave the belt loose enough so the longest section can be twisted 90 degrees. 

How and when to change your car’s auxiliary drivebelt

How long should a drivebelt last?

Typically, if there are no oil or coolant leaks degrading them, modern rubber belts will easily last 50 or 100,000 miles. 

But you should inspect them every 30,000 miles for cracking, contamination, fraying, or loosening of tension. 

How to change a drivebelt

  1. Firmly apply the handbrake, then jack up the front of the vehicle and support it securely on axle stands (see Jacking and vehicle support ). Remove the right-hand roadwheel.  
  2. Where fitted, undo the retaining bolts and remove the engine undertray, then undo the two screws and remove the drivebelt lower cover.  
  3. Engage an open-ended spanner with the lug at the top of the tensioner arm, then rotate the tensioner arm clockwise to release the belt tension. Insert a 4.0 mm diameter drill bit or rod into the hole in the tensioner body, so that the tensioner arm rests against it and locks it in this position. It is useful to have a small mirror available to enable the alignment of the locking holes to be more easily seen in the limited space available.  
  4. Note how the drivebelt is routed, then remove the belt from the pulleys. Note that if the belt is to be re-used, mark the direction of rotation. The belt must be refitted the same way round.  

Refitting the drivebelt

  1. Fit the belt around the pulleys, ensuring that the ribs on the belt are correctly engaged with the grooves in the pulleys and the drivebelt is correctly routed.  
  2. Using an open-ended spanner, hold the tensioner arm so that the locking drill bit/rod can be removed, then release the pressure on the spanner so that the automatic tensioner takes up the slack in the drivebelt.  
  3. Refit the drivebelt lower cover and, where applicable, the engine undertray. Refit the roadwheel then lower the vehicle to the ground and tighten the wheel nuts to the specified torque.