740 alternator brush wear

I have an apparent alternator problem with my 87 740 GLE. Per my Haynes
manual I removed the regulator/brush assembly and found that the rear brush
(closest to regulator) was probably just about at the 5mm spec distance at
the low point of its concave and the contact edge was blackened. The other
brush was several mm longer with a shiny contact edge. Am I right in
assuming the bushes need replacement? Is the uneven brush wear typical? Is
there generally good success in replacing just brushes ($3 at FCPGroton) or
regulator/brush assembly ($24 at FCPGroton)?

 

best to simply replace the whole regulator
assembly. you don't want to chance the problems of
possible overheating of the regulator from the too
close contact of the brushes.

 

Uneven brush wear is not a good sign, make sure you feel the sliprings with
your finger to make sure there isn't a nick or crack in one wearing down the
brush. I've always replaced the whole regulator but if it's in good shape I
suppose it'd be worth trying to replace the brushes, I didn't know it was
possible.

 

Also make sure that the brush is not binding in it's holder which tends to
cause arc burning of the brush.

Cheers, Peter.

 

I always replace the whole assembly. Usually I'll Start the car and
carefully polish the slips rings with a piece of scotchbright. The
brushes always seem to arc more on the rear side than the front. Uneven
wear is not unusual.

Bob

 

Thanks for the tips. I bought the new assembly but I can't figure out
the technique for getting it in place. Since the new brushes are quite
long it seems it would be best if they could be compressed while sliding
the assembly in. I tried placing a screwdriver in the cavity of the
alternator such that I could push the unit down onto the screwdriver,
compress the brush springs, and then push the assembly in but I think
I'm bumping into the conducting clip spring. I also tried tilting and
inserting various ways but I just can't get it to seat properly and I'm
starting to chip the ends of the brushes. Anyone know the trick?

RC

 

It's tough but you just have to work at it and eventually you'll get the
angle right and it'll just slide into place. Don't force it too hard as you
can crack the plastic. I've found that on 240's it's virtually impossible to
get it in without removing the alternator, but 740's are quite a bit easier.

 

It's been a while, but IIRC I tied thread to the braided wires on the
brushes and pulled them back while putting the regulator on, then broke the
threads off.

Mike

 

Here's how I got the regulator/brush assembly seated. I noticed the
original assembly had small holes in the bottom of the outside housing
walls and there was a small channel in the housing partition that keeps
the two brushes separated. It was evident that the brushes could be
pushed all the way into the housing and some straight, fine, stiff wire
could hold them in place by passing through the two holes and the
channel. Once the assembly was seated the wire could be withdrawn.
Unfortunately my replacement part didn't have the holes or channel but I
used the same general idea. I drilled a 1/16" hole through the bottom
of the wall at the end of the housing that extends deepest into the
alternator. Then I unfolded a paper clip and made a small hook in one
end that could catch in the hole while the long length of the clip wire
was pressed against the bottom of the housing holding the brushes up in
the housing. Once the assembly was seated I pushed the wire forward
enough for the hook to clear, twisted, and then was able to pull it out.

Neither assembly allowed me to see any of the braided wire so the idea
of tying thread to those wires was not possible. As for trying to tilt
and slide, I wasn't successful and each time the brushes got a little
more nicked. My first impression is that the alternator is OK but I'll
need to determine that over the next couple of days.

Thanks to all who offered suggestions.