trailer brake woes and troubleshooting

[crispyboy]

Hopefully some of you guys can help me troubleshoot some electric brake issues.

First let me set up my tale of woe.

Last fall we purchased a used Airstream travel trailer that happened to have new Dexter backing plates and drums installed. In spring 2012 I pulled the wheels for brake inspection, greased the wheel bearings, installed new wheel seals and reassembled. The brakes are Dexter electric 2" x 12".

The brakes have always been weak at best on this trailer. Loaded up and ready for a weekend of fun it weighs ~8k.

While on a recent trip out I noticed one wheel was extremely hot while driving in some stop/go traffic. I did some troubleshooting last week and I found that 3 of the 4 wheel seals had went bad, leaked grease, ruined the brake shoes and one of the magnets (magnet resistance was 9. 8). The magnet facing on the 3 of the drums were also deeply grooved. The fourth brake never did work because the installer of the new backing plates and drums caught a magnet wire behind a bolt that holds the backing plate to the axle flange.

I installed 4 new packed Dexter backing plates, 2 new grounding lugs for the 12 volt system and had the magnet facings machined on 3 of the drums before we left on last weekends outing. The brakes were still weak.

When coming home yesterday I had to make a u-turn in a parking lot and the emergency brake was accidentally activated at 20 mph. Only one brake locked up. This accident told me that the umbilical cord is probably working fine.



I believe my trouble lies within the trailer wiring. Does anybody have a diagram of how trailer brakes should be wired? Dexter told me to use a single ground vs. other information showing separate grounds for each magnet. I believe the Airstream trailer is currently wired using a single ground. I assume I have a bad connection in an area that's not presently visible.



Wanting to test the Prodigy controller the manual lever was used and the test meter showed 12. 26 volts at the rear bumper of the truck. Is there a way to wire an ammeter into the blue wire of the brake system? The new magnets show 4. 5 ohms of resistance each.

 

[BSeyler]

Somewhere, I have a dexter troubleshooting manual in PDF form. I'll look around tonight. You can put your ammeter in the supply line to each brake to see what each individual magnet is drawing. Seems like 1. 5 to 3 amps, according to Dexter, but I will double check. I could be wrong on that.

 

[RustyJC]

Dexter says their electric brakes should be wired in parallel, not in series.



Rusty

 

[BSeyler]

Dexter says their electric brakes should be wired in parallel, not in series.

Rusty

And, if you want them to work properly, Do Not ground to the frame. Run a common ground wire back through the plug to a ground source on the tow vehicle.

 

[RustyJC]

And, if you want them to work properly, Do Not ground to the frame. Run a common ground wire back through the plug to a ground source on the tow vehicle.

If you run such an isolated ground, you'd better also run it to the negative terminal of the 12VDC trailer battery (or series wired 6VDC batteries, if so equipped) if you want the breakaway function to work.



Rusty

 

[B.G. Smith]

I previously owned two different Airstreams, a 79 26' and a 78 31'. The breakaway switch on both were wired directly to the brake circuit and not through the umbilical cord. The Airstream has a sub frame over the axles if I remember correctly and if you ground to that and also ground from the cord plug to the "A" frame in front you should be good on the ground circuit. I had to rewire the cord on mine as it was not wired according to the standard wiring for RV trailers. They had round terminals in the plugs rather than flat. I would say for one thing, if the brakes locked up on one wheel with the emergency breakaway and you can't lock it with your controller you either have a defective controller or a defective circuit in the brake wiring. bg

 

[RustyJC]

I previously owned two different Airstreams, a 79 26' and a 78 31'. The breakaway switch on both were wired directly to the brake circuit and not through the umbilical cord. The Airstream has a sub frame over the axles if I remember correctly and if you ground to that and also ground from the cord plug to the "A" frame in front you should be good on the ground circuit. I had to rewire the cord on mine as it was not wired according to the standard wiring for RV trailers. They had round terminals in the plugs rather than flat. I would say for one thing, if the brakes locked up on one wheel with the emergency breakaway and you can't lock it with your controller you either have a defective controller or a defective circuit in the brake wiring. bg

B. G. ,



The breakaway switch normally only carries +12VDC from the battery positive to the trailer brake positive lead when the breakaway lead is pulled. The trailer battery negative is normally grounded to the frame and depends on the trailer brakes being grounded to the frame as well in order to complete the -12VDC side of the circuit. If the brakes were NOT grounded to the frame as was suggested earlier (see post #4) and the separate trailer brake ground that was suggested did not pick up the frame ground, where would the trailer battery complete the -12VDC side of the circuit unless the separate trailer brake ground were run to the -12VDC side of the trailer battery (batteries)?



Rusty

 

[B.G. Smith]

Rusty, I think we are both saying the same thing. The trailer battery is already grounded to the trailer frame, the 12v line to the breakaway switch comes from the trailer battery. Evidently his breakaway switch works, on one of the trailers I had, the fiber that the contacts in the switch were mounted on were warped so bad that when the switch was tripped the contacts didn't touch. The trailers I owned had a big fuse panel in the front inside trailer. bg

 

[RustyJC]

B. G. ,



I think we probably are as well. I was just pointing out that if post #4 was read to state that the trailer brakes SHOULD NOT be grounded to the trailer frame, then the trailer brakes wouldn't have a complete circuit back to the trailer battery on the negative side unless the isolated trailer brake ground recommended in post #4 picked up the trailer battery ground as well.



It sounds like the OP's problems are in the trailer brake wiring if the breakaway switch will only lock up one brake and all four brakes (and magnets) are OK otherwise.



Rusty

 

[crispyboy]

I looked at the very rough wiring schematic in the owners manual. I believe there is a ground bar near the 12v distribution panel where all the ground wires (from tow vehicle, brakes and various points of the trailer) are tied together and are also grounded to the trailer frame.
This is the next place I plan on checking when I get some time this week.

I have read where the brake wiring should be wired in parallel with the wires being all the same length from a junction box near the center of the axles so the braking is more equal.

Reading all the replies helps me to think through what I may have missed on my own. Thanks.

 

[BSeyler]

B. G. ,

I think we probably are as well. I was just pointing out that if post #4 was read to state that the trailer brakes SHOULD NOT be grounded to the trailer frame, then the trailer brakes wouldn't have a complete circuit back to the trailer battery on the negative side unless the isolated trailer brake ground recommended in post #4 picked up the trailer battery ground as well.

It sounds like the OP's problems are in the trailer brake wiring if the breakaway switch will only lock up one brake and all four brakes (and magnets) are OK otherwise.

Rusty

Rusty,

You're right. I should have said to not depend on just grounding to the frame. A dedicated ground from the brakes to the tow vehicle will help to eliminate resistance from corrosion that may occur where the ground wire attaches to the frame, but that attachment point (frame) is needed to complete the breakaway circuit.

Bud
On Edit:

When I got home, I had to go look at my gooseneck to see how I did it when I re-wired it over the summer. The brakes are not grounded to the frame. They are grounded to the tow vehicle via a 12 ga. wire. At the front, I do have an attachment from the ground wire to the frame of the trailer. That will compete the circuit for lights and allow the break-away to work.

 

[BSeyler]

crispyboy,

I found my PDF guide from Dexter. It has about 18 pages and should answer any questions you have. PM me with an e-mail and I can send it to you.

Bud

 

[RonD]

Your trailer is like 18 years old, I would just replace all the wiring connector to brakes, you want to ID all the wires at the wheels, test and mark all the hots with red, or better use a plug in connector at all the brakes, then do the same with the grounds, on your brakes there is no pos/neg on the brakes, but all the hot ones must be connected to the same wire, get a good ground, and make sure your controller is working correctly, patching that old wiring isn't worth the effort.