W126 failed alternator, DIY repair?

[jkeith]

Rescued by the AA after a the engine cut out in bank holiday traffic. The AA man's tester showed the alternator was not charging.

Am I correct in assuming that this will mean replacing the alternator and is this a DIY job? I see there are two 13 mm bolts but not sure how the belt tension is released.

Any helpful advice would be appreciated, thanks. Keith

 

[grober]

Its possible that its just the alternator regulator/rectifier pack at the rear of the unit has failed. Its a lot less expensive to replace than a complete alternator. Any good vehicle electrician should be able to repair it if you don't feel up to the job.

 

[jkeith]

Thanks Graeme, is it possible to test the regulator / rectifier or is it a case of replacing the parts and using the process by elimination?

 

[Steven Stoole]

Thanks Graeme, is it possible to test the regulator / rectifier or is it a case of replacing the parts and using the process by elimination?

Once you get the regulator out have a look at the brushes on it. there are two brushes on them and once they have worn to a certain length they dont make proper contact. If the regulator was shorting or if your alternator had a short in it, it would normally blow a fuse. I did mine not so long ago. It is not an expensive part and they are readily available. Hope this will help.

 

[jkeith]

Thanks Steve, my fuses all seem to be ok. I'll certainly do more exploring to pin point the exact fault. I'm not sure yet what the regularor looks like but assume it's the Bosch cylindrical unit at the back of the alternator on the left hand side (when standing facing the engine from the front).

 

[Dieselman]

If the red charge warning light glows dimly at all times the rectifier pack is blown, if the alternator fails to charge either it isn't being fed with +12v on the trigger line so the dash lamp won't illuminate at all, the earth strap is loose, or the regulator pack has failed.

After coursery examination i would go with the regulator.

 

[jkeith]

That's very helpful thanks Dieselman. There are no lights showing so I will check the earth connections and go for the regulator. Hoping to get the faulty parts identified tomorrow and replaced asap.

Many thanks, Keith

 

[grober]

Here you go [YOUTUBE]WYvZRz5Truo[/YOUTUBE]

 

[Vlad]

I have a man who charges £60 to diagnose the problem...mostly the regulator pack on the back and to fit a new one. Im sure he would be happy to get yours in the post and then send it back.

Top man and very much of the old school of mend and repair.

 

[jkeith]

Thanks Graeme, perfect description on you tube. My local auto electrician is closed until Tuesday so I'll be looking for a replacement regulator from him.

Vlad, thanks for your offer but I'm hoping I've got it cracked. On another matter, your handle includes many Merc cars, do you have a web site?

 

[jkeith]

Dead easy job! Thanks for all the good advice. I bought a replacement regulator for £10. The old unit had one brush shiny and the other was black. The auto electrician suggested the copper surface could be damaged and the alternator could be duff.

I was very suprised at how little of the brushes were left. I fitted the new unit in a matter of minutes and the multi-meter showed a very healthe 14.39 with the engine running. Job done.