3B Alternator needs brushes?

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Sep 12, 2004
I've noticed over the last 6 months or so that the "Brake" light stays on after I start my BJ42, but goes away once I start driving. I thought this was a fault in the indicator circuit for the handbrake, but now the light comes on pretty consistently when the truck drops down to idle speed, and goes out when it revs up. I thought that the brake light was also also a "Charge" light in TLCs - am I wrong? How should I diagnose beyond putting a meter on the alt outputs?

I think your right with your thinking. When the light comes on, go and put a meter across the battery posts. If it reads around 12 your not charging.. then have some one increase the rev's til the light goes out and check your voltage at the battery.

Might be time for brushes and/or regulator. My Mercedes is starting to do the same thing now... ah
Brush replacment is quick and easy. The hard part is R&Ring the alternator. The vacuum pump is conviently in the way. Take the brush block to the local starter/alternaror repair shop and they can match/replace the brushes quickly and easily. You can do it yourself if you can operate a soldering iron. Check the bearings for slop/leaking grease, clean the sliprings with a pencil eraser, and you are done!
Really one of the easier jobs on the cruiser, I have done starters and alternators on my Suzuki Samurai, BMW 2002(1974 year), Landcruiser and even airplanes. simple technology that has not changed in 50 years.
Go fer it
P.S. diagnostics, the reason that the light stays on during idle is the brushes are not making good contact with the slip rings, but when you rev it up the increased vibration causes the springs to force the brushes into contact with the rings, the increased speed also creates more electricity. Sooner or later the springs will not extend the brushes any further and no more electrons for you.
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Also, if you don't want to screw around with it, you can take the alternator in for a rebuild and get them to wind it so you get a bigger output. This is useful if you are running extra lights, stereo, etc. The only thing to make sure of is the splines at the back of the alternator are fine. I did that mistake once, got mine rebuilt then 8 months later the vacuum died. I cracked it open and found that the teeth on the splines were worn out too much. Damn pump on back of alternators - who's the genius who thought of that?
The brake light in a BJ42 does not tell you about charge, rather it tells you about the amount of vacuum in the vacuum tank, the level of fluid in the reservoir and whether the hand brake is engaged. I'd check these things first.

There is the possibility of the light staying on if the level of charge is so low, the the system does not recognize the engine as "running' since there is no charge... this is a "less likely" option.

I'd check the vacuum first, with a gauge - a weak vacuum pump or leaks could be ther result. Also check the drain at your vacuum tank for oil in the tank (means your check valve in the alt is needing some attention).

Next I'd check the output voltage of the alt (look for something around 28.8V). Then check the load the alt can carry... turn on your lights, heater etc... and then re-check the output voltage again - it should not drop too much.

Be sure that your fuseable links are in good shape (green plugs near the battery - usually on the left side), and that your connections at the battery posts are good (and all other significant connections). Also, make sure that the "engine" fuse is clean and functional.

If your alternator was weak (old brushes - avaialble at the dealer. no need to remove alt to change them) the batteries would go flat after a few days of driving depending on how much you use your lights, heat etc.

Good luck.

I had the same problem on my bj60, brake and filter lights on at idle. I had a bad diode. Pull the alternator, check the brushes, and if the look okay then dissassemble the alternator and check your diodes with an ohm meter. Mine was bad on the ground side.
I have the same issue with my brake light staying on. I checked my alternator its only putting out 27.5 volts and drops when I turn on lights, heater etc. I replaced my brushes about one year ago, I will recheck brushes. I am thinking I might have a voltage regulator issue. My Bj has a voltage regulator attached to the firewall, any idea how to check this?
Relay clicking when red light flashes

When my red light flashes at idle I can hear a relay cutting in and out, Upsidedown is this an indication that its low power or is there a relay in the low vac circuit??


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