Alternator brushes fubar?

[kim0663]

Dash warning lights (charge, hand brake and one more can't recall) all turned on so figured Murphy had struck me yet again.
Multimeter tests concluded I was not getting any charge at all.

The above procedure is over a period of 2 weeks or so. Dash lights came on and off intermittently so I think it was charging/not charging randomly. However the lights stayed on permanent recently and finally pulled the alternator out today to take a look.

Brushes looked worn with lots of brush dust/gunk everywhere including between the two brushes but not worn to a point where it would lose contact with the shaft.
Unfortunately I didn't think to test shorting between the brushes before I pulled the brushes out/cleaned them.

I have no knowledge on how to test the rectifier as this is the first time I've actually pulled an alternator apart but I am hoping they are fine.

Now the question is, if the gunk (which would contain metal particles due to worn brushes) between the two brushes were conductive (short circuit somewhat), would it have had an affect on the operation of the alternator? I have cleaned it all up and have assembled it again and continuously get 4.x ohms between the two screws that bolt the brush assembly onto the alternator while spinning the pulley as hard/fast as I can by hand.

Alternator was not charging at all when tested at the battery. Car is an sw20 with 3sgte if it makes a difference.

The brushes look serviceable to me so the only method to test with my limited knowledge/equipment is to put it back in the mr2 and start it up. It'd be awesome to have some confidence that I won't have to take it out if the brushes/shaft looks all good to some electrical guru here! Should I be worried and be prepared to rip it out again because it's not going to work?

[matt dunn]

Your brushes are past it, and the slip rings on the rotor are probably getting close to the wear limit.

When the brushes wear to the point where they are the brush springs are too far extended to keep enough pressure on the brushes and you get arcing from the brush to the rotor, which wears the slip rings.

Brushes are cheap as and easy to replace,
sliprings are a PITA and time consuming so expensive to fit,
and you really need to know what you are doing to connect them,

so if I was you I would clean the rotor sliprings
but dont put them in a lathe,
and fit a new set of brushes.

Also on a side note, dont ever fit slip rings to a race car alternator,
or something that will see high rpm for long periods of time.
They wont last.

[allencr]

The brushes look to have a lot of life left in them, maybe a little smegma causing them to stick/hangup & not make firm contact, and would be working OK if that rotor's slip rings weren't horribly worn & are the real cause.
Yeah, new brushes will fill in the gap until that nasty surface wears'em out in a month or two.

[DVSMOTORSPORT]

The brushes do look a bit past thier liftime, BUT, theres is a lot more to an alternator than just brushes.