One Hot Brake 21RB

firsthere · 10-11-2018, 10:31 AM

The Driver side rear brake on a tandem axle platform is running hot again. This is after adjusting the shoes twice and even replacing the entire assembly, backing plate, shoes, bearings and drums.

This has been going on since new. I have had to rotate the tire out at that location twice as they wear much faster than the others.

Could the wiring be supplying more voltage to this brake or ??

**Bama Rambler** · 10-11-2018, 10:43 AM

It's more likely that the wiring is supplying less voltage to the other brakes due to bad connections. So you're having to overcompensate for the lesser braking of the other brakes by raising the setting on the controller and that's causing the one good brake to do most of the braking.

There's a slight possibility that the other brakes have magnet issues or maybe grease on the shoes if you haven't checked them.

If you haven't checked the other brakes, I'd suggest that you do that, and check all the wiring connections to the brakes. Be sure to check the ground side as well.

firsthere · 10-11-2018, 10:56 AM

The brakes had a problem with the grease seals while under warranty. FR gave me the 4 assemblies but would not install them which I was fine with.

I replaced the Passenger front and Driver rear at the same time as they were overheated from the grease on the shoes. Each received new water tight electrical connections. I went over all of the drums and bearing at that time not so much the wiring though.

Where are the grounds are you referring to? Tks

**Bama Rambler** · 10-11-2018, 12:23 PM

Sometimes the brake magnets are grounded to the frame right at the wheel and doesn't run back to the 7-way through wiring. It's that grounding I was talking about.

It probably wouldn't be a bad idea to check the resistance of each brake magnet also.

firsthere · 10-11-2018, 04:10 PM

OK these are wired thru the magnet 1 in 1 out no ground. One notable item is the brake circuit is wired down the driver side, the problem brake is closest to the 7pin. Each axle brake has a splice on the DS side then thru the axle to the passenger side brake, possibly there is a short inside the tube.

Scrapper · 10-11-2018, 05:07 PM

Quote:

Originally Posted by firsthere

OK these are wired thru the magnet 1 in 1 out no ground. One notable item is the brake circuit is wired down the driver side, the problem brake is closest to the 7pin. Each axle brake has a splice on the DS side then thru the axle to the passenger side brake, possibly there is a short inside the tube.

I don't understand what you mean by "1 in, 1 out". Your trailer brakes uses DC volts to operate. There will always be a positive wire into the brake magnet and a ground wire out of the brake magnet. Now, whether the ground is attached to the frame near each tire or the ground is attached to a wire leading back to a central point, it's still a ground.

TheGerman · 10-11-2018, 05:35 PM

Quote:

Originally Posted by firsthere

OK these are wired thru the magnet 1 in 1 out no ground. One notable item is the brake circuit is wired down the driver side, the problem brake is closest to the 7pin. Each axle brake has a splice on the DS side then thru the axle to the passenger side brake, possibly there is a short inside the tube.

Yeah that doesn't sound right, it may not have been wired correctly from the factory. All 4 brake magnets should have a connection from the brake wiring and a connection to ground. See here: https://www.etrailer.com/question-69080.html Note the ground connections may also be all connected together and terminated at the junction box in the front of the trailer.

Scrapper · 10-11-2018, 07:51 PM

Make sure the magnets are wired in parallel.

If the brake magnets are wired in series there will be trouble from the voltage drop. Each magnet will get less voltage thereby doing less work. If one magnet fails, they all fail. If either the positive or ground wire to one magnet breaks you will loose all the brakes.

firsthere · 10-12-2018, 08:36 AM

The ground on each is not at the brake it runs back to splices in the main feed wire. It does appear to be wired in parallel, No loop. The driver side sees the voltage 1st as it then travels thru each axle to the pass side. Tks.

I plan to raise the TT and test if a brake does not function. Is it OK to pull the emergency breakaway pin to test? I heard they can be difficult to reset.

**Bama Rambler** · 10-12-2018, 09:17 AM

Make sure the tow vehicle isn't hooked to the RV if you pull the breakaway. Some vehicles brake controllers don't like being back-fed.

To me it's actually a good idea to pull the breakaway switch once a year or so to make sure it works, and to make sure that you can reinsert the plug in case it gets accidentally pulled. just be prepared to disconnect the battery(s) if you can't put the plug back in.

Don't leave it pulled very long, but just long enough to test the brakes won't be a problem. If you have a DC amp meter that will handle the current, you could test the amp draw of each magnet while you're testing. Each magnet should draw between 3 and 4 amps at 12 to 13 volts.

I would also connect the RV to the TV and have a helper operate the manual lever a little at a time to see if one brake locks up a lot before the rest.

firsthere · 10-12-2018, 09:25 AM

Good advice, and no Amp meter just a Multi. The problem with testing the wiring is there is so little protruding from the axles (1") I may have to pull new wire if I redo the Water tight connections. Or I could shave some insulation and retape but hate to do that.

BTW; what should the resistance be on the magnets?

**Bama Rambler** · 10-12-2018, 12:12 PM

Some multimeters can measure up to 10 amps DC.

As it turns out the resistance is between 3 and 4 ohms each.

firsthere · 10-12-2018, 07:34 PM

I checked braking on all 4 wheels and the one problem driverside rear locked up none of the others. There is a consistant humm on all and 1.9v on each . leaning back towards a mechanic issue.

babock · 10-12-2018, 10:44 PM

If I ever redo the wiring on my brakes, all 4 of them will be home runned to the tongue, including ground and they will be joined together there in a junction box. Makes trouble shooting way easier.

**Bama Rambler** · 10-13-2018, 06:55 PM

Quote:

Originally Posted by firsthere

I checked braking on all 4 wheels and the one problem driverside rear locked up none of the others. There is a consistant humm on all and 1.9v on each . leaning back towards a mechanic issue.

Are you saying that they all hum at 1.9 volts and the one locks up at that voltage?

firsthere · 05-12-2019, 08:23 AM

After some analysis, the problem brake magnet was rattling inside when the wheel was rotated, unlike the others. It seem there maybe some sort of defect there so I replaced the (new) backing plate assembly with the old one. I will keep an eye on it next outing.

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