(ET) Brushes, 3 years on.

[Chris Zach <cz beaker crystel com>]

Got the new brushes (thanks Harold!) and compared them to the old ones. 
One brush was down over 50%, the other 75%. So there was a lot of wear, 
and a lot of carbon in the endcap. Maybe the springs are too tight, it's 
a new carrier as of 3 years ago, so I'll try to unwind the springs some 
and see if I can reduce the tension a bit. Both new brushes move in 
their carriers, so no binding there.

Was looking at the ground fault, it's definitely in the heavier armature 
field winding and on one side (brush) I can see a resistance of 0 ohms 
while on the other side I see a resistance of .02 ohms. I need to use my 
fluke meter to test in more detail, but it does look like the short is 
on the armature wire side, probably close to the top of the coil. I just 
wish I could figure out how to get the coils out; it looks like the 
series field winding is separate from the normal shunt field so I might 
even be able to just have that re-wrapped.

Any idea how I can get the very large screws loose? Is there a high 
quality large flat bladed screwdriver to 3/8 air impact wrench around?

Another option is to just connect the other brush right to the other 
bolt and completely bypass the series field. Not sure what that would do 
to the tractor, field strength would NOT increase under heavy load, so I 
might want to disable field weakening. Still, when you run the tractor 
in reverse the field *does* weaken under load and it hasn't destroyed 
the tractor. Are the other motors (E12 and E15) also compound motors?

The ground fault is bad, annoying, and needs to be removed. I don't 
think it's faulting to armature (moving the armature around does not 
ever interrupt the fault) so it is probably to case. Maybe I'll try 
sliding a plastic shim plate between the winding and the case, see if I 
can interrupt it there. Otherwise I think I'm doing to ditch it.

C