Cheap and Easy Car Alternator Repair

Cheap easy fix to revive your car alternator

This instructable shows you how to replace brushes and the regulator for classic British car alternators, but the approach should be applicable to most other alternators.

The back story, my wife got stuck recently on the side of the road where her classic MG Midget’s battery went flat and she couldn’t start the car. She had to call Roadside assistance who checked the battery and alternator, when the car was running the voltage at the battery was barely above 12v, it should be around 14.3v to charge the battery. Hence this indicated alternator issues. A new alternator for these cars is worth about $200 plus fitting if done by your local garage, but often it is worn brushes that stop the alternator from charging the car battery and these are easy to replace.

All you need is a socket set and spanners plus a brush and regulator replacement kit for your model of alternator. So I ordered a brush and regulator repair kit for $30, once received and after tinkering for an hour and a half I had installed the kit and had replaced the alternator brushes and regulator. When checking the voltage at the battery when the car was running with lights and wipers on was the voltage was 14.4v, yippee, it’s done!

A cheap and easy fix to an otherwise expensive problem. So here’s how I did it…

Step 1: Before You Start, Purchase the Right Kit for Your Alternator

The assumption is that you have already purchased a brush and regulator replacement kit for the model of alternator you have before starting this instructable.

Step 2: Safety First, Disconnect the Car Battery

Disconnect the +ve from the battery for safety, I actually did not do this and bumped a +ve wire connected on the Alternator which created some brief fireworks, so my advice is to disconnect the +ve on the car battery first.

Step 3: Remove the Alternator

Take some photos of the alternator in position and the orientation of the wire harness, ie the wiring socket at the rear of the alternator. Before unbolting the alternator ensure you unclip the wire harness on the rear of the alternator.

You may have to google for details depending on the make and model of your car. But typically two bolts hold the alternator in place, one long pin bolt on the underside of the alternator and a short bolt through a slotted bracket on the top of the alternator. Unbolt both, the long pin bolt might take a little effort to remove, but patience and persistence you’ll get there.

Step 4: Remove the Rear Cover on the Alternator

Now you have removed the alternator, remove the plastic cover on the rear of the alternator, typically there are two bolts to be removed to remove the cover.

Step 5: Remove Old Regulator and Brushes, Fit New Kit

With the rear cover on alternator removed, take some photos of the regulator, and wiring to and from the regulator and the brushes. These maybe handy should you have issues refitting the wiring.

Now remove the old brushes and the old regular. When removing the brushes check the length of the old against the new to see how much the old have worn.

Install the new regulator, and note wiring instructions from the supplier with the upgrade/repair kit. Install new brushes, reconnect wiring and refit bolts, tighten (be mindful not to over tighten as the bolts are probably screwing into brittle plastic). Double check wiring against your previous photos and the instructions that came with the kit.

Step 6: Refit Rear Plastic Cover

Refit Black plastic cover to the rear of the alternator.

Step 7: Refit the Alternator

Refit the alternator back into your vehicle and make sure the fan belt is tight.

Step 8: Now Run Some Tests to See If You Have Fixed It

Attach your multi-meter +ve to car battery +ve and multi-meter –ve to car battery –ve, set the multi-meter voltage range to 20VDC or the next above whichever is available on your multi-meter.

Start the car and check voltage, hopefully if you have replaced the brushes and voltage regulator according to manufacturer instructions you will see a reading of +14.3v or thereabouts (14.2 to 14.5ish), this means the battery is being charged and the alternator is now working as designed.

If it’s still reading 12v then you have other problems and I would recommend starting with this youtube video from Chris Fix.

To wrap up this instructable, hopefully this has been of use to you. I literally saved my wife and I well over $200 on this simple fix and you can too.