[Handy930]

My 1991 300E 4matic died while driving. Battery dead. I jumped it the next day and was able to drive a short distance to a service station. They charged the battery. Checked out the battery and alternator,and diodes all OK. Drove home 5 miles. Next morning checked the battery 12.4 volts with engine off. 14+ volts with idle speed. Drove about 25 miles and it all happened again. The terminals are cleaned. Charging battery now and hope to get the car home today. Any thoughts or experience out there? What about the OVP relay? Checked the 10 amp fuses and are OK. Anything else to check before I give up and go to the dreaded dealer.

 

[Uboater]

There are only a few things that go bad on alternators . Brushes get too short to make steady contact - Diodes go ( you said they are good)-regulator ( it wouldn't charge at all or cook the battery ).Bearings ( remove the belt and shake the shaft).

You could have a shorted cable or bad starter relay, Rare ,Draining current.

I always recommend having your battery load tested for free at an auto parts store.Can the battery crank steady 30 seconds at a good speed ?

Batteries dieing / radiators leaking / air leaks on tires ,,, cost way more ,if not replace the time a problem is found .

 

[Handy930]

When it dies there is no 30 seconds of cranking. I am going to have the system tested again tomorrow at a parts place and Sears(it's a DieHard). I have to think it is the alternator. It might be putting out voltage but not the amps. Still trying to understand the relationship to the VOP relay that some talk about. I am paranoid about going to the dealer where they are accustom to deep pockets. I have been keeping older Mercedes and Porsches going myself for years, but this has me stumped. Thanks for your thoughts.

 

[Handy930]

Fixed I think. Took the alternator in for check and brushes and commentator are bad. I was told it would probably test enough volts at idle without much load, but crash with rpm and load. Get it back today and will try it out.

 

[Uboater]

NICE Fix ,,,,, In the go old days you could buy a KIT $29 bearings ,brushes ,diodes . In 30 minutes it was ready to run. I love it when its a cheap fix.

Not to be a wise ass , its a slip rings on an alternator ,not a commutator ( that's more motors or DC gens )

 

[Handy930]

All is well. I should have followed my gut and did the alternator straight away, but the service guy gave it a clean bill. Live and learn and try to remember the next time. Great fix at $100.