alternator brushes causing this?
 

i've been reading search threads, but am not satisfied with what i'm reading yet. i think i have the stock marchal alternator still in my '74..three years ago i had a shop inspect it and they said it was okay, but my car is a daily driver so it has had probably another 20,000 miles or more put on it since then. for nearly a year i've noticed that i tend to keep a very, very dim glow on the alt light even after the diodes have come online (revving up to between 1500-2000 rpm).

typical symptoms are i'm listening to the radio on high volume and it suddenly quits - i can either reduce volume or do something else to reduce load like turning down a/c fan speed..or i could turn off my headlights (if i didn't need them). this is definitely a load-related issue and is certainly worse at night because i'm running headlights, but it's annoying..everytime i come to a stop i have to turn volume wayyyy down because engine speed isn't great enough to keep alternator output high. does this sound like an alternator that's just reaching its life limit? does this mean just replace brushes? thanks.
ryan

Ryan,

Worn-out brushes can cause dropouts if they lose contact with the slip rings ... but it also could be the VR or a grounding problem at the relay/regulator panel! I wouldn't make the assumption that the alternator needs replacement due to aging alone, though!

The dim-glow alternator warning lamp problem is unlrelated, as that is a classic problem of buildup of Voltage drops over time in the many connections between instrument panel and alternator ...

looks like a problem. tested my system voltage with an analog meter..11-12 volts battery only..12 volts with engine running..turn up radio volume to loud still 12 volts..headlights on still 12 volts..a/c on still about 12...rev engine to 3k and get about 13 volts..
ryan

Ryan,

Sounds like it is time to pull the alternator and get it tested ...

With those Voltage readings it is impossible to tell whether it is a regulator or alternator fault. My hunch is regulator ... but you can't tell for sure until the alternator is tested!

Is there no test for the regulator?

Ah yes...another victim of a faulty regulator.....

Mine did the same thing. The radio would cut out with the RPMs over 2000. If you just replace the VR, that may not correct the problem, because the brushs for the VR rub against a copper plate. The plate (part of the alternator) gets worn through, so just replacing the VR does not help.

I thought he had the external regulator?

i have the external regulator, but i want to check its part number.
ryan

I just posted under "jumping RPM needle" that it had a similar problem with my tach. I replaced the VR but when I inspected the alternator, I noticed the brushes had worn the copper rings pretty thin. I still have the jumping needle so I am thinking that I need to have the alternator tested as mentioned above but who would do this type of test? Do I need to take the alternator to a Porsche specialist or would any good auto replace shop be able to do this? What about auto part stores? Thanks for the advice.

innov8,
innovative name, btw..;) actually you want to take it to an alternator/starter repair shop..they tend to repair both of these types of components. as a matter of fact, i read the thread you mentioned and i have recently had just a very little amount of tach wiggle as well. usually in my case it has meant time to change my ignition points, but this would fit along with the rest of the pattern. i'm really thinking tomorrow i will pull my alternator and inspect the brushes..
ryan

Thanks Ryan. I will check back with you tomorrow after I have checked the points and coil. Then, if that doesn't solve it, I will pull the alternator as well. Thanks again for you help. Patrick

patrick,
if your engine is a stock '82 i don't think you have points after all..warren corrected me in another thread..and on this board there's warren..and then there's god..;)
ryan