How to Replace your Serpentine Belt

Friday, 19 April 2024

If you know your way around a car’s engine, then you’ll know what a serpentine belt (or drive belt) is. Automatic belt tensioners are now standard in most cars, so replacing a serpentine belt is one of those jobs that it is possible to do yourself.

Here’s our DIY guide to how to change your serpentine belt.

Mechanic holding car engine belt part

What is a serpentine belt?

A serpentine or drive belt is important in a car because it transfers power from the engine’s crankshaft to numerous key components of the vehicle, such as the alternator, air conditioning compressor, power steering pump and water pump. But the belt will wear with age and can develop cracks, so it might need to be replaced during the lifetime of the vehicle.

Older or classic cars will have multiple belts and should be replaced by a professionally trained mechanic.

How will I know it’s time to replace my serpentine belt?

Most belts last between 50,000-100,000 miles. If you hear a squealing or squeaking sound coming from your engine, then chances are it is your serpentine belt slipping and sliding. This means it is wearing out and you should get it replaced as soon as possible.

Before you start …

Check the tensioner belt

It’s important to ensure that the tensioner itself is where it needs to be before you think about swapping the belt around: a good tensioner belt needs to exhibit a slight vibration of around 1/32 inches or less of movement, and the belt should be able to move smoothly, with no jerks or visible vibration. If this isn’t the case, then the tensioner is bad, and will need to be replaced first. This is not a DIY task – take it to a mechanic!

Check the belt actually needs replacing

Typically, serpentine belt cracking is most likely in older belts. If you’ve got cracks in more than three adjacent ribs of the belt that are bigger than an inch or so – or there are four or more cracks per inch on one of the ribs – then the belt will need replacing. It will also need replacing if you notice any of the following:

Chunks missing from the ribs
Torn or frayed fabric
Glazing on the belt’s back
Debris trapped anywhere in the ribs

In the case of more recent belts, cracking is less common and you’re better off looking for wear. Wear is harder to locate than cracking, but there are actually smartphone apps that can detect wear, or you can use a conventional belt wear gauge.

Where does the serpentine belt go?

Each belt will snake round the engine in a different way, so make sure you know where to put the serpentine belt replacement. Check your car’s manual for a schematic diagram of the belt or search online. It may also be worth taking some photos of the engine from different angles.

Changing your serpentine belt: step by step

Remove the old belt

First you will need to release the tensioner which keeps the belt taut as the car is moving. Use the serpentine hand belt tool to rotate the tensioner in order to remove tension from the belt. You might need a ratchet or breaker bar to do this, or a socket on the pulley. The belt should be fairly easy to remove but take care not to disturb any of the pulleys. Slowly release the tensioner once the belt is off.

Check for misalignment and other signs of damage

This is a good opportunity to check for any signs of misalignment on the old belt. These won’t be fixed by replacing the belt. If there is any disintegration along the edges and separated ribs, then you could have misalignment issues. Remove any dirt and grime from the pulleys and look for oil leaks. Check the tensioner pulleys are spinning correctly – they shouldn’t make a noise when they spin. If there is any excessive movement on the pulleys, from side to side or in and out, they will fail and so will your drive belt, meaning instant loss of power to the vehicle.

Install the new belt

Using the belt tensioner tool, you can then route the new belt around the belt path. The belt will usually need to go first around the crankshaft pulley, and then the grooved ones. Finish the job by sliding the belt into a rounded, non-grooved, smooth roller. Make sure the belt is completely on and centred on each pulley and tighten the pulley with the tensioner tool. Slowly release the tensioner and start the engine. Keep the engine idling for a minute or so to make sure the new serpentine belt is working as it should.

Changing a serpentine belt FAQs

What tools do you need to replace a serpentine belt?

You will just need a new belt, a belt tensioner tool and a socket wrench to replace your serpentine belt.

How long does it take to change a serpentine belt?

If you have the right tools and do some basic prep it should take about 15 minutes to put a new serpentine belt on. If you want to know more about doing more car maintenance yourself, we have a range of handy guides.

Find engine parts at ASM

Here at ASM Auto Recycling, we can help with your search for replacement parts for your car. In our used car parts store you can search by your car registration, make and model and find all the parts that we have available for your vehicle. These include oil filters, fuel system parts, engine and transmission parts. You can also use our parts enquiry form. Plus, we offer a 90-day parts peace of mind guarantee for fitting used replacement engines or car parts purchased from ASM.

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