Electric Brakes

[GMarugg]

I recently purchase a 1982 Excella. The only real pull I have done with it was to a local repair shop to have some work done on it. The trailer brakes appeared to work properly at that time. Since then I have purchase a 2015 GMC 2500 for a TV and replace the emergency stop switch that was disconnected when I purchased the trailer. I was going to replace the wheel bearings and started with the driver side front wheel. After I got the wheel back together and the tire was still off the ground I decided to check the brake and found that I had no brake when I pulled the emergency stop or pushed on the Pickup brake. I did have about 11 volts at the connection to the wheel magnet and the wheel magnet showed to have a little less than 4 Ohms resistance. I took a compass by each wheel, with the emergency switch pulled and it still showed correct north. I show real high resistance to the chassis on each of the wires coming to the wheel magnet. Does anyone know where the brakes are grounded to the chassis? Any helpful Ideas?

[carl2591]

you sure the magnets are actually in the wheels?? energize and see it they are actually trying to "stick" to the metal. wheel.

[idroba]

With a full 12 volts between the magnet wires each should draw about 2.5 to 3 amps. So the set of 4 should take 10 to 12 amps. Any less indicates that one or more of the brake magnets are not working.

It is VERY common to have high resistance or no contact between the magnet wires and the ones coming from the AS wiring system. Often they are connected with wire nuts and water gets in and corrodes the connections. I have seen green corrosion working up the original AS wires 6 to 10 inches under the insulation. I think the negative wire on the AS brake wire side connects to the general white wire negative side system somewhere up front where the white wire comes from the umbilical cord. And somewhere there about the white negative wire is also connected to the frame.

The magnet wires are interchangeable, does not matter which is connected to + and which to - but of course both have to be connected to make the magnet work.

[HowieE]

Originally Posted by GMarugg

I had no brake when I pulled the emergency stop or pushed on the Pickup brake.

Please give another explanation as to what you mean here.

Depending on what type of break controller you have applying the TV brakes while at a stop will not activate the trailer brakes.

Now if you manually applied the trailer breaks with the manual slide lever on the break controller you should have had breaks power to the trailer i all is wired correctly.

The compass test will show application when using the manual slide lever on the break controller. Make sure your break controller is not powered off while the ignition is off. Some newer TV do this.

[GMarugg]

The brake control came as standard equipment on the GMC 2500. As I have about 11 volts at the end of the wire going to the magnet when I pull the emergency stop switch, the brake coil has about 4 ohms of resistance, there has to be some other reason none of the brakes appear to be functioning. I have to suspect the white wire is not connected to the chassis.

[nrgtrakr]

"Does anyone know where the brakes are grounded to the chassis? Any helpful Ideas?"

I think the two wires connected to each of your individual brake magnets are connected both to the umbilical cord (blue hot, white ground) and your 12vdc distribution box.

With a wheel in the air and the breakaway switch in broken away mode, the brake should not allow you to rotate the wheel - either with the 7 way attached to the TV, or without and your house battery is charged.

With voltage present (across the two wires) and nothing happens (to include deflecting a compass), and the wheel can be rotated, the magnets need replacing.

At least this is what happened when I tested mine after repacking the bearings and adjusting the brakes once I got it home. One brake had a broken wire, so out of curiousity I looked at the schematic - and without physically tracing it down, that is my best guess - 7 way and 12vdc distribution panel.

For the first tow home the brake controller was the test; locked them up with the lever rolling slow, adjusted accordingly and rechecked once I got to the first downhill. Amazing with only 3 of 4 working.

[HowieE]

Originally Posted by GMarugg

The brake control came as standard equipment on the GMC 2500. As I have about 11 volts at the end of the wire going to the magnet when I pull the emergency stop switch, the brake coil has about 4 ohms of resistance, there has to be some other reason none of the brakes appear to be functioning. I have to suspect the white wire is not connected to the chassis.

There are 2 wires going into the backer plate. One is supply voltage to the magnet and the other ground. If you are measuring 11 volts from one wire to chassis ground but not getting brakes to work that would indicate the brake ground wire is open. You should find it grounded to the chassis up front either underneath the trailer or in the connection box where the U cord connects.

Remove the wire nut on the second wire and check for continuity between the it and chassis ground to verify if there is an open of the ground wire. If you have continuity from the second wire to chassis ground the wire going into the backer plate may be open inside the backer plate.

[GMarugg]

I was looking at an AS drawing and the only ground it showed on the brake system was though the connection plug to the chassis ground on the TV.

[GMarugg]

Yes I replaced the wheel bearings and looked at the magnet before I put the hub back on.

[HowieE]

Originally Posted by GMarugg

I was looking at an AS drawing and the only ground it showed on the brake system was though the connection plug to the chassis ground on the TV.

That has to be a mistake. The Emergency break switch would not have a ground if the trailer became free of the TV and the pin pulled. Besides you can activate the trailer brakes by jumping the trailer battery and break terminals on the U cord without the TV attached. Do not do that unless you are using a #12 wire as it will melt in your hand if you do.

The breaks are grounded to the trailer chassis.

[GMarugg]

Thanks for all the helpful information, I appreciate the info.
I took the wheel apart again, looked at the wiring, manually adjusted the brake, grease every and put it all back together. It now appears to be working correctly - don't know why?

This model has the DC panel and DC converter at the very front of the trailer. I can verify that there are two solid wires grounded to the chassis at the front of the trailer. It would be on the outside and just below where the DC panel would be on the inside.