How to repair, change or replace an alternator

How to change an alternator

Changing your alternator isn’t a job for the average DIY enthusiast. It requires someone with a good knowledge of motor repairs and mechanical competence. If you’re not confident about the task in hand, you’d be much better advised to leave it to the professionals.

An alternator is an electrical device located in your car’s engine bay. Its job is to generate electricity to charge the battery. It does this through a connection to the engine drive, and while it’s rotating, it creates electricity.

The electricity is created when the rotor, a selection of spinning magnets, passes at high speeds over a nest of copper wires, called the stator. A regulator is also part of its components, to make sure the right amount of electricity flows around the vehicle.

You’re going to need a range of tools, the new alternator and a replacement alternator belt. Among those tools, you’re going to need a belt tensioner tool, a voltmeter, and a few other bits and pieces to keep life nice and simple.

Step 1 – Safeguard your vehicle’s electronic preset information

Depending on your vehicle and the repair manual requirements, you may need to use a memory saver to capture all your electronic preset information.

Once you’ve got that sorted, disconnect the negative battery cable.

Check your alternator belt to determine whether it’s a V-belt or a serpentine belt. A serpentine belt will be flat and thin with ribs on the underneath. A V-belt (no surprise here) is in the shape of a V. If your alternator utilises a V-belt, you can jump to step 5.

Step 2 – Loosen the serpentine belt

The belt tensioner is spring-loaded, so be very careful that you don’t suffer an injury if it snaps back into place. Keep your hands clear whenever you can. The job will be a lot harder if you have to do it with just one hand!

Loosen the belt tensioner to gain easier access in removing the belt. You may need to be patient with the belt as it can be quite tricky to relocate or remove.

Step 3 – Remove the belt

Once you have loosened the tensioner, it should make removing the belt much more straightforward. At this point, it’s a good idea to check the working order of the belt tensioner. If it doesn’t run smoothly, is rusty, or snags at all—now’s the time to have it replaced.

A belt tensioner tool will give you extra leverage and better access to tight areas. If you don’t have one, you should consider adding one to your toolkit. It makes the job a great deal easier than a standard socket wrench.

Step 4 – Remove all the connected parts

Be sure to label all the wires and fasteners so you can be confident of which goes where when it comes to re-assembly.

Step 5 – Loosen the alternator

If you do have a V-belt, then you must loosen the alternator before you can remove the belt. It’s the alternator that provides the tension for the belt in these cases, not a separate tensioning part as with the serpentine belt.

Step 6 – Install the new alternator

You want to ensure a nice snug fit. Line up all the bolt holes and tighten the bolts to the correct tension.

Replace all the connecting components to their correct counterparts (as you previously labelled).

Next, replace the belt. If you struggle a little with this, there are a few tricks on how to get the belt back on your alternator. Some alternators have a transverse bolt that will allow movement of the alternator on its bracket. This allows adjustment to the belt tension.

If there is no transverse bolt, you can use a ‘cheater’ to hold the alternator in place while you tighten it into its correct position. Alternatively, a good assistant can help you keep the belt tight while you fasten the mounting bolts.

Step 7 – Check the belt tension

Without the correct tension, you’re in danger of creating real problems. Check your repair manual for just how tight your belt should be. After a few days, you should recheck the tension to be sure it’s still correct after a period of settling in.

Step 8 – Reconnect the battery

Reconnect the negative terminal of your battery, attach your voltmeter and start the car. The correct output of your alternator should now show a reading of 13.1 to 16.5 volts. If your reading is correct, then you’re all done. Pat yourself on the back and reward yourself with a good cup of tea.

How much is it to replace an alternator?

Replacing an alternator at a garage will cost around £200 or £300. You can expect higher prices from dealerships and car franchises.

For higher-end cars, obviously, you can expect the price to go up accordingly there as well. You could pay between £500 and £1000 for a luxury model’s alternator replacement.

How to repair an alternator

Again, this isn’t a job for just anybody. Repairing an alternator isn’t for the faint-hearted. It’s not overly complicated, but considering the good running health of your car depends on it, you want to be 100% sure you can carry the job out successfully.

You’ll need the correct replacement components and your fair share of patience.

First, you need to remove the alternator from your car, as outlined in the above process. Then you’ll need to remove its plastic cover and check that the bearing is ok. It needs to be snug. If it’s at all loose or jams, then it needs to be replaced.

Next, remove the resistors to access and remove the rectifier. You’ll need to disconnect the soldered wires before undoing the mounting screws. Then you can replace the old rectifier with its replacement—soldering up the wires to reconnect them.

It’s important to clean the armature shaft while replacing the brushes—this is your next stage. Check the springs are correctly located when remounting them in place.

The only thing left is to replace the voltage regulator. If you got this far, then well done! That’s how to rebuild an alternator. All you need to do now is fit it back into place, get the belt back on and check that the whole thing works!