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Date: Wed Apr 27 18:23:02 1994   
From: John De Armond
Subject: Re: transfer pump innards

emory!!bmw-request writes:

>>  Can it be replace with another type of a metal rod?

>no.  metal is too hard.  If you open up a AAA battery you will find a
>carbon rod inside.  Maybe you can try to cut it to shape.  But I've
>kludged carbon brushes before (on a 2002 blower motor), and it's a
>difficult job.  It's impossible to buy new ones so you're probably
>better off just replacing it.  

Lots o bad information.  Carbon brushes really are not and a carbon
rod from a dry cell will not work.  Carbon brushes are made of 
various mixes of copper powder, graphite powder and clay binder.  The
graphite powder provides lubricity AND tunes the resistance of the brush
so that when it shorts the commutator bars, the current is limited
and sparking thus controlled.  

There are at least 4 easy places to find the brushes.  From the description 
of the brushes, they sould almost identical to those used in Bosch alternators
and similar to those used in older Mopar alternators.  Therefore your 
friendly local auto parts store should be your first stop.  If they can't
find something close, look in your yellow pages under "auto electric" 
and call the companies listed therein.  These companies specialize in 
rebuilding automotive generators, alternators and motors and are generally
quite reasonable.  If for some reason that fails, look in your yellow
pages for "electric motor repair/rewinding".  Check with the motor repair
shops.  Most such shops keep a large selection of standard brushes.
Failing that, look for appliance repair parts and call those stores.
Many small appliance motors use similar brushes.  Finally, if all
this fails, call the motor repair shop back and ask to buy either some 
brushes which are close OR a suitable block of brush carbon.  You should 
select a compound with a similar appearance and "ohms per square".
You can measure this by placing your ohmmeter points on your brushes 
and then placing them similarly on the new carbon.  The matching doesn't
have to be real close but you don't want 98% copper fork lift brushes
for such an application.  This stuff works very easily with a file
so shaping the brushes appropriately is easy.  If you can't find 
a brush with the appropriate pigtail, don't worry about it.  In this
application, sufficient current can travel through the holder and
spring without overheating.

This actually took me longer to type this in than it does to execute.


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