Many of your engine's ancilliary components are driven by at least one auxiliary drivebelt, also known as a serpentine belt. It operates in tough conditions such as extreme heat, freezing temperatures and at considerable tension. Since rubber is an unpredictable material, even under ideal conditions, belt failure is one of the most common causes of vehicle breakdowns.
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 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 to be replaced
The auxiliary drive belt 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, especially at startup, or when you turn on the air-con, 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 old, hardened or contaminated and no longer grips 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 auxiliary belts all you need to do is pry the spring-loaded tensioner away from the belt and pull the old 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 or take a photo before taking the old belt off. Your Haynes manual will also show you the routing.
With proper routing confirmed, pry the tensioner again and put the new belt into place over the last pulley. Be sure the belt is sitting in the centre of all the pulleys and not off to one side.
On vehicles with manually adjusted belts, you’ll need to loosen a component or crank the adjuster bolt to release the belt tension. Once the new belt is fitted, tighten the adjuster bolt to get the proper tension. The general rule of thumb is to leave the belt loose enough so the longest section can be twisted 90 degrees.
How long should a drivebelt last?
Typically, if there are no oil or coolant leaks degrading them, modern rubber belts will easily last 50,000 to 100,000 miles.
They should be inspected for cracking, contamination, fraying, or loosening of tension every time the vehicle is serviced.
How to change a drivebelt
Watch this video to see how it's done. Find the full step-by-step task for your model.
These are instructions for a vehicle with a tensioner arm. Yours may differ.
- Firmly apply the handbrake, then jack up the front of the vehicle and support it securely on axle stands. Remove a wheel to boost access, if necessary.
- Where fitted, undo the retaining bolts and remove the engine undertray, then undo screws and remove the drivebelt cover.
- 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.
- 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
- 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.
- 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.
- 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.
Tools you will need
Only basic tools are required for this job, although you will need to raise the car if you have to remove the undertray/wheel/wheelarch liner to access the belt(s).
- Trolley jack
- Axle stands
- Spanner set
- Drill bit/rod/Allen key set
- Screwdriver set
Parts you may need
How much does a new auxiliary drivebelt cost?
Garage fee savings