Trailer brakes work then don't..

[Duckless]

I have a car hauler, with two standard 3.5k axles under it. I lost a bearing and subsequently had to swap another Dexter axle under the trailer while 7 hours from home on a trip. Ever since then, my trailer brakes work for about the first braking event, and then after that I have basically no trailer brakes. You can feel them activate, but the truck is doing all the work.

This occurs with the same brake controller (in two different trucks) and another brake controller in another truck. Prodigy P3 controllers if that matters. Can turn up brake boost and that does nothing. Manual activation gives no change. Controllers work great for other trailers.

I've rewired the trailer brakes, going to a heavier gauge, just in case. No change. Went from a clockwise pattern linking each brake, to a Y- split, running down each side. Brakes on the other axle were two years old and low miles.

I don't really know where to go from there. Hoping one of the many knowledgeable people of this forum knows something about trailer brakes. Any ideas what could be wrong?

 

[PontiacHO]

Are you actually getting electrical current to the brakes? Sounds like poor connection.

 

[supton]

Sounds like a connection problem. Check the ground wiring. Wonder if the new axle somehow is not tied to chassis.

 

[mk378]

Make sure the new axle is installed correctly and not flipped left to right. The brakes are built different for the left and right side and will not work if put on the other side. On a Dexter brake with the magnet at the bottom, the magnet arm faces the front of the trailer. If it was a used axle (or even if it is a new one) you'd want to remove both drums and check for damaged magnets or wiring inside the drum.

Electrically, all brake magnets are wired in parallel like lights are. There is always a two wire connection to each brake (power and ground) since the axle can't be trusted to have a ground path through the suspension. The path of the wiring (bus or star) does not matter.

I suspect there is a short circuit that saps the energy from the controller, though this should throw an error on the controller display. You could temporarily hook up only one axle or even only one brake at a time and test drive each one to isolate problems. Wiring a light that you can see from the cab to one of the wheels would show if the brake is receiving power.

 

[D60]

Yep you want the arms at front.

Other than that, poor ground or low voltage.

I'm sure you're not using Scotchloks, right?

 

[D60]

In considering further, I'd try to power various bulbs from each gnd/power combo to simulate various amp loads. I bet you've got a circuit "falling on its face" under load.

Sitting overnight (or whatever) may reestablish enough contact for the first use of the day to work good enough. Flakey connections are really weird.

But if you believe all wheels to be affected, it's likely the incoming blue wire or overall trailer ground.

 

[Duckless]

Sounds like I have a project this weekend. I'll tear into those brakes and verify they are facing the right way. Seeing as how I didn't know they had a left and right offhand, I'll be checking that. At least I don't remember offhand, but it's possible they were labeled when I bought the axle and that was done right. It's been a busy couple years.

Connections are all soldered. Voltage was measured at each brake and, besides minor voltage drop as I got further, it was getting the voltage shown on the controller.

Thanks for the tips guys! I don't tow super heavy with the trailer, but it would be nice to have the peace of mind it will work every time.

 

[D60]

Sounds like I have a project this weekend. I'll tear into those brakes and verify they are facing the right way. Seeing as how I didn't know they had a left and right offhand, I'll be checking that. At least I don't remember offhand, but it's possible they were labeled when I bought the axle and that was done right. It's been a busy couple years.

Connections are all soldered. Voltage was measured at each brake and, besides minor voltage drop as I got further, it was getting the voltage shown on the controller.

Thanks for the tips guys! I don't tow super heavy with the trailer, but it would be nice to have the peace of mind it will work every time.

So you've checked voltage. Verify your primary ground is in excellent condition. If you're positive ground is good, then still test voltage with a load at the wheel(s). Powering a DMM or similar takes very little current, so it may read as having great voltage but fail under load. It could also be the blue wire contact in the trailer plug itself, or the ground contact I suppose.

I honestly don't know how many amps the magnets typically draw....?

 

[mk378]

One source I see says 3 to 3.8 ohms. That would mean the amperage would be 3 to 4 amps per wheel. It is normal for current to decrease some as the coil heats up because the resistance of wire increases.

 

[Duckless]

Brakes worked on this last trip better than they have in a long time. Fixed fully? Maybe. They brake pretty good, and most importantly they did this the entire trip instead of the first application of brakes and then disappear.

I pulled each brake drum and greased my bearings, cleaned them out, moved the magnets around and verified everything was in its place and nothing seized. All good there. Magnets on the new axle can swing forward and backward about 3 inches total and an inch side to side.. More than I'd expect and more than the old axle.

I went through the junction box and made sure all the terminals were tight, no loose wires, nothing chaffed or broken. Cleaned up my 7 pin connections just to be sure as well.

I then decided to add a wire to the trailer frame from the ground in the junction box as well. I think this is what the fix ended up being. So I'm guessing my 7 pin ground wire is not doing so good (a whole 3-4 years old).

 

[Chevyc10]

The 7 pin connector corrodes frequently. Have seen trailer lights on, not connected to vehicle. Connector corroded, I assume winch battery was powering lights. Feeding lights through battery charging wire in connector. I keep spare 7 pin on hand.

 

[meep]

I’ve had so many electrical issues with trailer brakes and an end to end rewire is about standard procedure for me now. My last TT however, I could never quite get right. They worked but were tepid at best. No way they could lock the wheel, at all. Felt like at best I got 50% out of them.

 

[D60]

I’ve had so many electrical issues with trailer brakes and an end to end rewire is about standard procedure for me now. My last TT however, I could never quite get right. They worked but were tepid at best. No way they could lock the wheel, at all. Felt like at best I got 50% out of them.

My '11 SuperDuty won't apply nearly full power with the manual lever. If I want to see if they'll lock up I have to Max Power (man: "Great name!" Homer: "Thanks, I got it from a hair dryer") with an empty trailer and slam on the brakes.

This has not been true of Prodigy P2s but apparently OEM TBCs try to out-think me.