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Old 01-15-2007, 01:49 PM
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Join Date: Dec 2005
Posts: 53
Thumbs up Alternator brush replacement

Replacing the brushes in a Bosch Alternator
...or how I fixed my alternator for dimes, literally.

1986 Mercedes-Benz 190E 2.3L 8V
The car started acting up while driving, the ABS light illuminated, the radio reception became poor and the lights dimmed. Shortly thereafter the engine sputtered to a stall.
After the car was towed home on a rollback, I found the battery was dead. The alternator must have stopped charging, forcing the car to drain the battery in order to run. If instead the battery had died while driving, the alternator probably would have kept the car running. Since my wife needed to use my truck now, I had to ride my bike on a 5-mile round trip to pick up the new brushes. Being low on cash, I raided the piggy bank for dimes and quarters, and paid for the new brushes with 22 dimes and got 8 cents change.
The alternator appears to be the original 1986 equipment. To keep costs low, I decided to avoid replacing it if possible. I priced out voltage regulators, and did some research. I decided to just replace the brushes in the voltage regulator. Here is what I did:
Disconnect the battery negative cable for safety.
Start by removing the heat shield and then the plastic cover on the back of the alternator. 8mm bolts, 3 long and one short. Don't lose the spacer sleeves between the plastic cover and heat shield. There are three.
Alternator brush replacement-000_1688.jpg

The regulator cannot be seen in the photo above, it is mounted on the bottom rear of the alternator, held by two flathead screws. You can unplug the connector on the alternator if needed (I wound up disconnecting it later during regulator reinstallation so I could see better). The connector is retained by a small wire which flips down once pried out slightly. Then carefully work the connector off, prying with screwdrivers or small prybar to help get the connector off. 3 spade type terminals hold the connector on.

Here is the regulator removed and cleaned up a bit:
Alternator brush replacement-000_1675.jpg
Note the brush length, no longer able to contact the slip rings of the rotor.
Alternator brush replacement-000_1676.jpg
The part number is 1197 311 009 (cross references to F4010-39368 new Bosch part #)
Alternator brush replacement-000_1683.jpg
Here you can see the other side where the brushes attach. The wires of the brushes come through the two square tabs and are held in place by crimped sleeves and solder. To remove the old brushes, file the tips of the crimp sleeves flat then make a punch mark carefully to help center the drill. On mine, I tried two methods. First I tried breaking off the crimp sleeve, but found I still had to drill. So the second one I just drilled all the way through. A sharp drill bit would have made it easier, but my broken, poorly resharpened bit worked with some patience.
Alternator brush replacement-000_1684.jpg
Drill out the old using 1/16 or smaller bit. I used 1/16 because it was all I had. It worked and left the holes slightly larger than necessary. A smaller hole will make it trickier to thread the wire of the new brush into place..
Remove the old brushes once the drilling is complete. A residual amount of solder might hold it in place, just pull it out. Then transfer the little white sleeves and the springs onto the new brushes.

Last edited by bbarcher; 01-15-2007 at 02:01 PM.
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Old 01-15-2007, 01:59 PM
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Join Date: Dec 2005
Posts: 53
Post ...continued

Thread the new brush wires into the holes drilled previously, and set them so they will not overextend and pop out. Keep in mind the twisted wire might stretch a little during installation and make one of the brushes pop out slightly (like mine did). Leave at least 1/8" of the brush in the holder so it is well supported as it wears and so it has no chance of popping out over the edge of the holder. If you do a decent drill job, you can reuse the crimp sleeve to crimp and hold the wire, then solder each wire carefully. Don't use too much solder. If you lack soldering confidence, this job may be best left to someone else, or just buy a new regulator. You might have to use a clamp or some novel way of holding the wire while soldering, depending on how the crimp sleeves are looking after drilling. If the drilled hole is too big, fill in the gap between the hole and wire by inserting some extra wire, to help keep the solder from draining down the hole. Once the wires are soldered, clip off the excess.
Alternator brush replacement-000_1685.jpg
Alternator brush replacement-000_1686.jpg
Alternator brush replacement-000_1687.jpg

Reinstalling the regulator can be tricky. It is easiest to do it with the alternator sitting on the workbench, but I did it with the alternator still on the car. I ended up unplugging the plug on the alternator for a better view. I also had to find a way to keep the brushes held in while trying to line up the screw holes. I pushed the brushes in, then wrapped a long twist tie around it to hold them. Then I screwed the regulator on partially and carefully removed the twist tie, releasing the brushes to extend and contact the slip rings. Then I did some final tightening of the screws and reconnected the connector for a voltage test.
The battery voltage went from 12.45 off, to 13.8 volts engine running. It works, yay. Eventually I would like to upgrade the voltage regulator to gain more charging voltage like others have done with these Bosch alternators. There are adjustable regulators and regulators with a higher voltage setpoint that will charge about 14.2-14.5 volts under most conditions. Many feel that 13.8 is too low for optimal charging performance, and I agree. But I have not had any dead battery problems when the alternator is working in daily use. And this is a stock vehicle, so the $2.12 brushes work for now.

Parts needed:
New aftermarket brushes were purchased at a local Alternator shop: Northwest Starter & Alternator, 7106 Eckhert Road, San Antonio, TX (210)-521-0011
I also found that Bosch brush sets can be purchased from most online Euro parts dealers, use part number 1 127 014 011 (cross references to F4121-36736)
Alternator brush replacement-bosch-alternator-brush-set-part-number-1-127-014-011-f4121-36736.jpg
These usually sell for $5-7 plus shipping. They appear to come pre-shaped to the slip ring's arc, whereas mine were arced differently, as if to be used in a different application. The guy just matched them based on size, so they must be some universal rebuild parts. I made no attempt to try to reshape mine, but some people try to match the arc to establish good contact right away. Mine seems to be charging fine, hopefully it will last another 150,000 or so miles. The old ones lasted somewhere beyond 115,000 because the odometer was inop when the car was purchased.
Beware that a worn slip ring surface can consume brushes at an unacceptable rate. So make sure to take a mirror and flashlight and check for any anomalies, verify that the slip rings have a smooth surface. Some people recommend deglazing the surface with some fine garnet sandpaper. I didn't do this.

Good luck, I hope this helps somebody.
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Old 01-15-2007, 02:14 PM
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Nicely done thread!
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Old 01-17-2007, 01:44 PM
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Thank you!
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Old 04-01-2014, 03:13 PM
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Join Date: Jun 2006
Location: Portland, OR
Posts: 39
Where the heck do you walk into an auto parts store and just pick up a set of brushes in stock for $2.12? I've called all the major and some of the minor parts stores in Portland asking about these things, and nobody I've talked to can believe somebody is trying to just get brushes for the voltage regulator.
I've bought these brushes online and done this job two or three times. It's great. Thanks for the writeup.
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Old 04-01-2014, 04:49 PM
Join Date: Mar 2009
Location: Iceland
Posts: 423
New regulators are a dime a dozen.
600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.
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Old 02-15-2015, 01:14 AM
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Join Date: Feb 2015
Posts: 1

Im sorry, I'm new, I'll learn to keep my mouth shut, but not tonite. I couldn't even read all that, let alone DO all that work. It's only $20. bucks for a new regulator, and believe me, I am a real cheapskate. I refuse to call a mechanic because HE will charge HER(me) about $500. to fix that problem. I'll go out tomorrow, give it a quick cleaning with a brush and if that doesn't work, I'm off to the parts store for a new regulator. Then I'll put it on myself with help from the Manual I just bought on Ebay for $9.99. But thanks for the point in the right direction.

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