Electric trailer brakes locking while reversing

[Nick G]

Yesterday we arrived home from a trip and began to back the trailer into the driveway when the trailer shuddered. I did a walk around the rig, nothing of note. Continued backing up watching more carefully and the trailer sort of hopped a few times. It seemed the brakes were catching and locking the wheels which popped the trailer up on the suspension arms then the wheels would release and lock again. I kept going back to clear the street and the issue finally stopped. To test that it was the brakes I manually applied the brake controller which caused another brief lockup.

Has anyone else had this issue? Any tips?
The brakes are electric, new last year and re adjusted this spring. They aren’t capable of locking up going forward, I’m not sure why they are catching so hard in reverse.

[Raspy]

Is it possible you have the brakes reversed? Left one on the right side and right one on the left side. This would make them much weaker going forward than in reverse and you might have the brake controller turned up high to compensate, which would make them grab harder in reverse.

[Randyag]

I had this problem years ago, every time I backed up I had I had to get out and unplug the wiring. I didn't like the wiring on the trailer, I rewired a lot of it, after I did that and made sure it was wired correctly, I no longer had the problem. Not sure exactly what was wrong but it was 100% something wrong with the wiring. Good Luck

[Nick G]

I didn’t know the brakes were directional but I also didn’t install them, they came with my new axle. Any tips on how to tell if they are installed backwards?

I’ll keep the wiring in mind but it seems unlikely since all the wiring from the plug to the brakes is all new. The truck side is factory so I suspect it’s ok too. I’ve read some people have had issues where the reverse lights short to the brakes but I assume that would result in a full lockup in reverse. This is acting more like the brakes are jamming themselves as soon as the controller engages them, sometime on their own, then suddenly release once enough pressure is applied.

I’ll have to get the trailer up on jack stands this weekend and start testing and probably take them apart to inspect.

[Raspy]

Originally Posted by Nick G

I didn’t know the brakes were directional but I also didn’t install them, they came with my new axle. Any tips on how to tell if they are installed backwards?

I’ll keep the wiring in mind but it seems unlikely since all the wiring from the plug to the brakes is all new. The truck side is factory so I suspect it’s ok too. I’ve read some people have had issues where the reverse lights short to the brakes but I assume that would result in a full lockup in reverse. This is acting more like the brakes are jamming themselves as soon as the controller engages them, sometime on their own, then suddenly release once enough pressure is applied.

I’ll have to get the trailer up on jack stands this weekend and start testing and probably take them apart to inspect.

It may be a long shot, but worth checking. And the symptoms match with the theory. As far as I know, all electric brakes are semi-self energizing. As the brakes are applied going forward, the shoes try to follow the wear surface in the drum and that force helps apply them. In reverse, the opposite is true and they are inherently weak. So if yours are backward, they would hold better in reverse than rolling forward. A clue from you is that they won't lock going forward, but lock too easily going backward. And since they are weak going forward it is likely you have the gain all the way up. Which, again, means they would hold too much going backward. It's just something to check.

Every set of brake backing plates I've purchased was marked left and right. Sometimes it is stamped into the backing plate and sometimes it might just be a tag.

You could simply look online and find a Youtube about doing brakes and see how the backing plate in the video is arranged. The actuating arm that is attached to the magnet will be what you want to look at. The magnet rubs against the side of the drum, with a force proportional to the current sent to it from the controller. It moves with the drum and pulls the actuating arm, which rotates the cam, which spreads the shoes into the drum. Usually, one shoe pushes on a point on the backing plate, the trailing shoe. And one shoe rests against the cam, the leading shoe. When rolling forward the leading show will be toward the front.

[computerspook]

Well my first step obviously would be unplugged the plug while backing up and see if the brakes are on when backing up when not even the hooked to the truck. Makes for a really good question and a good way to divide and conquer the problem.

I would almost start asking if the whole axle was put on backwards.

I also have a trailer wiring Jack tester. It's like this t-handle thing with LEDs that I use regularly to check my tow vehicle wiring. If you don't have one get one give it a try. Just because something is new doesn't mean it was right

[Lloyd (aka Santa) Coltman]

Yup, when I read through the initial post, I wondered about the axle being installed reversed. Almost all 'drum' brakes are designed with 'self-servo' action, to increase braking force dependent on speed. The only brakes I ever saw that didn't do this were 'double trailing shoe' design, front brakes on a '54 Jaguar mk7, It was almost impossible to lock those front brakes, so, in a 'Panic' stop, the car would 'Haul down' dead straight.

[Nick G]

The axle is a trailing arm torsion axle so I’m confident that the axle isn’t backwards. The company the built the axle for me also installed the brakes so I can’t be sure those weren’t installed backwards. It’s a bit odd that the problem just started, if the brakes were backwards or I wired it incorrectly I would expect to have encountered this problem shortly after the install.
Either way, I’ll see if I can start ruling out electrical issues this weekend and then get into the brakes if needed. It’s almost a white out here with smoke which might hamper my enthusiasm.

[steve67]

If this is a new thing, is it possible that the brakes were wired to the backup light wire?

[djstump]

I know this may sound simple, but check TV brake controller to see how to set brake controller to backup trailer. Note, I usually unplug trailer from TV when parking trailer.

[Lloyd (aka Santa) Coltman]

Originally Posted by computerspook

Well my first step obviously would be unplugged the plug while backing up and see if the brakes are on when backing up when not even the hooked to the truck. Makes for a really good question and a good way to divide and conquer the problem.

I would almost start asking if the whole axle was put on backwards.

I also have a trailer wiring Jack tester. It's like this t-handle thing with LEDs that I use regularly to check my tow vehicle wiring. If you don't have one get one give it a try. Just because something is new doesn't mean it was right

The tester mentioned above s available (on sale now) at Princess Auto
https://www.princessauto.com/en/7-wa...t/PA0008271173
I carry one in each of my vehicles

[Guide Guy]

If you haven’t already fixed it here’s something that happened to us when camping in our Casita. We camped at the beach for a week and our battery kept draining with nothing on. We tried everything but nothing worked. When we hooked up to leave, I pulled away and the brakes were locked up, making the trailer hop and skid. We checked everything to no avail, when my wife said, “What’s this red plastic thing on the ground under the hitch?” Turns put the emergency brake breakaway plug had come undone, and the brakes we locked up for the week, causing the battery to drain. She inserted the plug and the trailer lurched and gave a huge thank you sigh as the brakes released. 😂 So, check that your plug is installed. Good luck!

[Lockman]

Nick, If you go to e-trailer.com you can see pictures of how the 7in electric brakes difference should look between left and right.

[computerspook]

Originally Posted by steve67

If this is a new thing, is it possible that the brakes were wired to the backup light wire?

Well one of many failures that should stop if you pull the plug and try backing up.


I see three possibilities with a lot of causes of each. And step one is going to be sperating out and eliminating the three options

#1 There is a problem with the TV wiring. Pull the plug and if the brakes stop trying to stop you then that is where to look.


#2 There is a wiring problem in the trailer. But for that to be a problem you will have to have power going to the brakes and a wrong route. With the plug to the TV removed also disconnect the battery. If this fixes it, then in some way it is an electrical problem in the trailer. The emergency brake mentioned above is probably not the issue as then they would be on all of the time, but it will be a case of divide out the wiring.


#3 If neither of these is the problem then it sounds like you have a mechanical problem and then that is time to get an expert involved. May need one for narrowing down the other options. But this one will pretty much be up to an expert.

[Nick G]

Thanks for all the suggestions, I’m still not sure what the issue is but have done some crude diagnostics.
No break away brake so that’s ruled out.
I put the trailer up on stands and rotated the wheels by hand to see if I could recreate the lockup, no lockup or unusual noise.
Hooked up the truck wiring, tested again, nothing.
With blocks behind the truck tires I had girlfriend put the truck in reverse and release the brakes, then plugged in the trailer and rotated the wheels by hand. I did get the drivers side to lockup once in this condition but couldn’t recreate it. Since it was only one side and there was no noise from the brakes indicating that they were receiving power, I suspect this was a fluke(or my girlfriend touched the brake pedal…)
Next we tested with the controller and the brakes locked up and with a bit of a grindy noise and feel on the driver side.
I pulled the drums off the have a look. Both sides look pretty good as far as I can tell. A bit of gritty mud had gotten in from a back road on our last trip. The driver side which seems likely the side that was causing issues has a broken retainer clip on the magnet. One half of the clip was sitting inside the hole in the magnet, the other half is missing. I’m not sure if that could cause this issue but it’s worth fixing.
I’ll order up the part next week and in the mean time I might test with my multimeter or pickup a test plug and see if that shows anything weird going on.
Perhaps it’s partially that the brake shoes have finally broken in and are grabbing much more aggressively than I’m used to. Maybe I need to turn down the controller a few notches? I’ve read that the 7” drums don’t have a lot of stopping power which has been my experience until now.
A wiring issue is still possible but if there is it could a PITA to track down since the problem is intermittent.

[Nick G]

I did check to see if the brakes were reversed and they are correct. They actually have left and right stickers on the inside and also matched pictures online.

[matthfam]

Originally Posted by Nick G

I didn’t know the brakes were directional but I also didn’t install them, they came with my new axle. Any tips on how to tell if they are installed backwards?

I’ll keep the wiring in mind but it seems unlikely since all the wiring from the plug to the brakes is all new. The truck side is factory so I suspect it’s ok too. I’ve read some people have had issues where the reverse lights short to the brakes but I assume that would result in a full lockup in reverse. This is acting more like the brakes are jamming themselves as soon as the controller engages them, sometime on their own, then suddenly release once enough pressure is applied.

I’ll have to get the trailer up on jack stands this weekend and start testing and probably take them apart to inspect.

If you installed the axle backward it would have the same effect. There should, I would think, be a notation as to which end of the axle is which ...

[Lloyd (aka Santa) Coltman]

That broken/missing clip could be the source of the problem, as it could cause the actuator to 'wedge' and jam. Keep us posted as to results when part is obtained/installed. I bought a set of 7" brakes to install on my original (almost 400 lb) M/C tent trailer, but instead designed and built a new trailer with more space, that scaled in at just 200 lb., loaded.

[Nick G]

I’m hoping that either the magnet/actuating arm were jamming due to the broken clip or that the missing piece of clip was in there jamming something up. It can be a real pain trouble shooting a mechanical issue when you can’t actually see what is happening inside the mechanism. The real trick will be trying to find a source for the clip without buying the whole magnet assembly. So far none of my local auto parts suppliers can get it and the one online source I’ve tried so far wanted $40+ to ship the $3 clip.

As for the direction of the axle/brakes. The brakes are tagged left and right and match the parts diagrams for the correct orientation. The axle is a torsion axle in the recommended trailing orientation. If you aren’t familiar with torsion axles, it’s easy to tell the orientation since the hubs are offset on torsion arms toward the front or the rear of the axle tube. Hubs toward the back is called a trailing arm and is the recommended orientation although many of the 13’ trailers, including this one, were originally designed with the axles installed in reverse. I now wonder if the brake may have been jamming in both directions but only became obvious when reversing since a lockup in that direction will lift the whole trailer as the torsion arm rotates.

[computerspook]

Originally Posted by Nick G

I’m hoping that either the magnet/actuating arm were jamming due to the broken clip or that the missing piece of clip was in there jamming something up. It can be a real pain trouble shooting a mechanical issue when you can’t actually see what is happening inside the mechanism. The real trick will be trying to find a source for the clip without buying the whole magnet assembly. So far none of my local auto parts suppliers can get it and the one online source I’ve tried so far wanted $40+ to ship the $3 clip.

As for the direction of the axle/brakes. The brakes are tagged left and right and match the parts diagrams for the correct orientation. The axle is a torsion axle in the recommended trailing orientation. If you aren’t familiar with torsion axles, it’s easy to tell the orientation since the hubs are offset on torsion arms toward the front or the rear of the axle tube. Hubs toward the back is called a trailing arm and is the recommended orientation although many of the 13’ trailers, including this one, were originally designed with the axles installed in reverse. I now wonder if the brake may have been jamming in both directions but only became obvious when reversing since a lockup in that direction will lift the whole trailer as the torsion arm rotates.

I might check with a truck repair place. They repair trailers too. Or most of them do. Now normally that is flat bed and cargo trailers and not RVs, but kind of the same thing. They might have the clips in stock. Auto parts place, not so much.

And this is a good contact to make anyway. Now most of their customers need the repair "yeasterday if not sooner" so they have to be staffed for immediately taking on jobs. So they end up with slack time. And if you can drop your trailer off and let them work on it in slack time you can usually get a discount. Or at least that is how it works around here.