# Need new Prestolite MTC brushes and springs



## EVfun (Mar 14, 2010)

I think I have been playing with the 1000 amp kick from the Zilla a bit to much for my old Prestolite MTC-4001. On 2 opposing sets of brushes (4 brushes total) the pigtails into the brush are completely burned off at the brush. On one side the brush holder has some minor zorch marks, small nicks a file can take care of easily. The brush springs on that side are melted too. The comm looks fine, with its pretty milk chocolate color finish intact. 

Why one full set of brushes, with no visible damage on the other set? What else should I look for in the motor? Oh, and where can you recommend I go for new brushes and springs? This is cutting into my summer fun!


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## EVfun (Mar 14, 2010)

Pictures or it didn't happen, right? I thought perhaps I would get some input if I added some pictures of the damage I cleaned up.

Inside shot of the cleaned up brush holder damage:









Outside shot of the cleaned up brush holder damage:









This is what the brush holder should look like:









The commutator seems to have survived without harm:









Here is a destroyed brush and a brush with no apparent damage:








The number on the good brush is still readable, "MGP-12F 7AA"

This is an overview of the cleaned up brush end bell:


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## major (Apr 4, 2008)

Hi EVfun,

Those brush holders cleaned up nicely. I can see some damage on the outside of one, but if the inside surfaces are smooth and the brushes slide up and down easily, they should work for you.

The comm looks pretty good. I can see some wear and some blackened area but would be inclined not to clean it or dress it unless there is a noticeable discontinuity or clicking of the brushes as she rotates. Then try a dressing stone and reseat (break-in the brushes). If that doesn't take care of it, have it turned.

I don't think those are original brushes. I think the factory brushes had the tamped pigtails. Those have a rivet. When the brush overheats, the solder on the rivet will melt and can solder the brush in place in the brass holder. Then it will eventually lose contact with the comm as it wears leading to failure. Get replacement brushes which use the tamped (without rivets) pigtails if you can.

Replace the springs with the new brushes. Searching on behalf of Chip, we did find a replacement brush holder assembly for about $100 IIRC, just in case.

Good luck,

major


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## EVfun (Mar 14, 2010)

A long time local EVer, Dave Cloud, came through for me with 8 new brushes with tamped pigtails instead of riveted leads. The leads are not insulated, so I will have watch where they land. He had 6 new brush springs too, so I will have to reuse some of the ones from the undamaged brushes. The brushes have the angle, but not the full curve of the commutator. I will wrap the comm in sandpaper and hand spin the motor to finish the radius. I copied this over to diyEV for the benefit of those reading who are not on this list. Thanks for all your help.

A couple of small questions, what kinds of sandpaper are suitable for wrapping the comm to seat the brushes? I was told to use garnet paper and avoid anything carbide. Should I lightly stone the comm with the motor running to remove the current patina? I've been told yes and no.


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## major (Apr 4, 2008)

Hi EVfun,

Yes, do shape the brushes. Garnet paper is o.k. http://www.diyelectriccar.com/forums/showthread.php?t=85491&highlight=garnet I think sandpaper is also. Wrap the comm with one layer. Masking tape to hold it in place. The thinner the paper the better to get the radius proper. Blow out the dust.

That shapes the brush. Seating requires running under load (current). No load with 12V gets you like 50A and isn't too bad but takes a long time. The contact surface of the seated portion becomes shiny. If you can't get a high percentage of the brush seated, take it easy driving the first hundred miles..... No 1000 Amp burnouts.

I'd use vicegrips with leather on the shaft to turn it to shape those brushes. Can you post a photo to show readers the rivet vs tamp?

I favor leaving film or patina on the comm alone, even when changing brushes, if you can. Some give advice to always turn the comm when replacing brushes. I'd do that only if there is damage to the comm or excessive uneven wear. Stoning will remove the film and smooth the comm surface. I'd do that if you have some burning or minor discontinuities causing noise or sparking at low voltage no load. If that doesn't help, then have it turned and undercut. Stone lightly after turning.

major


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## EVfun (Mar 14, 2010)

Here is a picture of an old brush and a new brush. You can see the difference in length as well as how the brush leads are attached to the brush.


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## EVfun (Mar 14, 2010)

I got the motor back together this morning. I precurved the brushes with a piece of fine garnet paper wrapped around the comm. I turned the motor by jacking one rear tire off the ground and spinning the tire in 4 th gear. After pulling the end bell and removing the sand paper I reassembled the motor and ran it no load for an hour. I found that hanging a closed end wrench over the stop on my potbox maintained a " fast idle." 

I grabbed my Palm and programmed the Zilla to boring. I was running at 450 battery amps and 900 motor amps when I toasted the brush leads taking off repeatedly in 3rd gear. Now I've set it to 300 battery amps and 450 motor amps, plus added a 100 volt motor voltage limit. I took it out for a nice mellow drive, using 2nd gear, and all seems well.


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