• From: Colorado Springs, CO
  • Registered: 2004-03-27
  • Posts: 3,622

Topic: Generator Brush Wear?

Hi, All: Quick question: Other than the mechanical wear on generator brushes from contact (friction) with the commutator, or perhaps from failing bearings on the generator shaft, are there any other factors which might cause the carbon/graphite brushes to wear prematurely? (6 volts by the way)

I'm asking because I replaced the brushes in April 2004 and they seem to be worn almost to the point of needing replacement. I've checked the generator shaft for axial and radial play and found none, or nothing obvious.  The commutator does not appear to have any rough spots or uneven sectors.  I've cleaned it up on numerous occasions and have always recessed the insulation between the sectors. The generator seems to be charging fine (no dead battery, no dimmer than normal lights, etc.) although I've not actually measured its output.

Is there something about the sparking (arcing?) between the brush and the commutator that would cause this? Or is this a case where the material used in today's brushes just doesn't match up to the brushes of old?!

Your thoughts on this would be greatly appreciated.

Clancy

  • TomB
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  • From: Austin, TX
  • Registered: 2004-03-27
  • Posts: 1,095

Re: Generator Brush Wear?

Good question Clancy. I noticed on my Vanagons recently that the replacement brushes didn't last like the originals, so finding a cause would be helpful. Afraid I haven't any answer tho.

  • From: Cincinnati, Ohio
  • Registered: 2005-09-10
  • Posts: 2,336

Re: Generator Brush Wear?

I can propose a some theories...

1.  Maybe the graphite or carbon that the replacement brushes are made of is not of the same density as the OEM brushes (less dense).

2.  Maybe the replacement brushes are made from a softer carbon / graphite...thus faster wear.

3.  Maybe the springs on the brushes are stiffer than the OEM brushes...thus more pressure on the commutator...thus faster wear.

4.  Maybe the replacement brushes are not as long as the OEM.

5.  Maybe a combination of 1 thru 4.

Just like other replacement parts for our air-cooled VW's...maybe replacements are not as good as the German OEM stuff.

Just some ideas.

- Nick

1979 Super Beetle Convertible
  • From: Vancouver Canada
  • Registered: 2004-04-28
  • Posts: 441

Re: Generator Brush Wear?

I have a friend who only gets 2 years out of a set.  On one of my cars I ran it for 10 years and never checked them.  One thing I noticed when I went for a ride with him is that as soon as the car was running, he pulled the headlight switch on.  The lights are always on for every second the engine is running.  He believes that daytime lights makes you safer.  He also wears out headlight switches.

  • From: Bethel Park PA
  • Registered: 2004-06-27
  • Posts: 686

Re: Generator Brush Wear?

Check this link - http://www.ecmweb.com/mag/electric_answ … en_common/ - about a quarter of the way down the page.

It gives an answer that I'm not sure is complete.  At least it isn't an answer we may have expected.

David H
'66 VW Beetle w/sunroof
http://tinyurl.com/qhw59
"Where am I going ... and why am I in this handbasket?"

6 Reply by CW

  • CW
  • Member
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  • Registered: 2005-06-20
  • Posts: 120

Re: Generator Brush Wear?

(The following comments are intended for those new to Kettering-type ignition systems, such as most Volkswagens, and indeed almost all cars manufactured before 1970, use. You old-timers are not likely to find much useful below.)

I note the explanation that arcing causes electrical wear. This squares with my experience, which is that too much current flow through the system results in excess arcing at the brushes, which in turn results in premature wear.

The individual who ALWAYS runs the headlights is probably causing ten years worth of the designed-in amount of ampere-hours to flow through the brushes in two years. So, that could still be normal wear.

If you go through a phase where the car is hard to start and you crank and crank and crank the starter all the time, that will definitely cause premature brush wear.

If you don't run the headlights all the time and don't have a lot of aftermarket accessories (like air-conditioning) that add to the current load of the generator, and you still have excessive wear, I would hook an ammeter up in series with battery lead and see how much current is flowing through the system with the key off.

How much is too much? That depends on your year model and how it is equipped. Some accessories (like the electric clock) will cause current to flow with the ignition off.  This should be on the order of a fraction of an amp (or, alternatively, not too many microamps). My stock '66 model does not have any current flow with the ignition off. Think about how your car is configured and use judgement.

If you're not sure whether you have excessive current flow,  remove fuses one at a time until the current flow stops, and then see which device(s) that fuse feeds. Common sense will often tell you whether the device(s) in question should draw current with the ignition off or not.

If your battery is always going dead AND you have excessive brush wear in the generator, you should be having a ''Eureka!'' moment right about now.

  • From: Colorado Springs, CO
  • Registered: 2004-03-27
  • Posts: 3,622

Re: Generator Brush Wear?

Thanks to you all; a good bit to digest and try to apply to our individual situations....

David's link brought an "a-hah!" when I read this:
"Also, very low humidity environments do not provide enough moisture for the formation of the lubricating film. If excessive brush wear is a problem in such an environment, you may have to humidify the area where the machine is operating."

When my Bug was operated in Southern California, and the brushes lasted 10 years could it have been from the rough average of 40% to 60 % relative humidity?? And now in Colorado, our relative humidity runs around 15% in the summer an often lower than that in the winter! Sounds like I need my swamp cooler pointed at my generator!  Seriously, I do appreciate the feedback on this question. It's always great to glean the collective wisdom of this site. 

Followup question:  I found the 12 volt VW number for the generator brushes as 111 903 515E and the 6 volt number as 111 903 515A. Does anyone have the Bosch numbers for the brushes?

Clancy

Clancy

  • From: Bethel Park PA
  • Registered: 2004-06-27
  • Posts: 686

Re: Generator Brush Wear?

If low humidity is leading to your higher brush wear rate I think that's an acceptable trade-off.  It's better than the negatives that might be associated with high humidity areas.

I'd rather replace brushes in a generator than take care of mold, corrosion, dried out fabrics, etc.

David H
'66 VW Beetle w/sunroof
http://tinyurl.com/qhw59
"Where am I going ... and why am I in this handbasket?"
  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,610

Re: Generator Brush Wear?

I just went to a local shop that works on Bosch stuff and he looked up my brush, which I brought in, in his computer then measured mine real carefully with a micrometer to make sure it was as described. There are one size fits all brushes because apparently there are two types of generator. A VW one that was made by Bosch and a Bosch one = same brush. The place I went to was called AltStartAir.

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now available
http://www.openroad.ca/volkswebbin/view … p?id=85915
  • Registered: 2007-03-27
  • Posts: 2,422

Re: Generator Brush Wear?

LMAO Vw generator made by Bosch ??????
Who said I was all wett didnt know what a VW Generator was ????
  Ok if Brushe's work ??/ If not good deal like I said is Kragen rebuild's by Auto lite .
I bought mine at Krak head Auto in AZ  << rann me 85 Buck's << Beat's 189.95  for a new Bosch ???
Like I said 2 types of caseing's Ive seen >> Smooth and then the circular lined Bosch !
  Ive bought both rebuilt !
I prefer the rebuilt one on the Bosch circular lined case !
                                                                                        Sean