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Old 05-21-2014, 08:34 AM   #1
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1964 24' Tradewind
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Brakes Grabbing

I had new axels, brakes and 7 pin connector replaced on the 64 Tradewind I am bringing back to life. But I have run into a problem. I am having trouble getting the cause of the problem figured out. The first time happened at about 4000 miles into a 6000 mile trip. The brakes worked for the first 4000 miles. I stopped for the night and the next morning when I would touch the brakes they would lock but then disengage when I would take my foot off the brake. Changing the gain on the controller had no effect on the grabbing. I nursed it along 5 miles to the nearest trailer doctor. They put a meter on it and at first they were not sure it was getting enough voltage to the controller but then decided it was. The only variable that changed in the process was taking the 7 pin in and out a few times. They said the brakes should be working and they were. My best guess was that maybe dust got in the 7 pin (although I am not sure I even disconnected it that night) No trouble for the last 2000 miles. Next trip was a short 20 mile camp outing with no problems. The trip after that was a 1000 mile round trip with no problem on the trip down but when we broke camp the grabbing was back. After about 20 miles of playing with the 7 pin the brakes worked fine all the way back home. I took it straight to my trailer guy who did the original work but of course we could not find any thing wrong because the brakes were working. They worked for the next 20 mile trip and then I put the trailer up for the winter. I just got it out yesterday to start some projects at my house and as I pulled out of my slot and touched the brakes they grabbed, so I drove slowly around the near by State Park with no problems. I had also moved around the storage lot a couple of times without trouble during the winter. Leaving the state park, I got a short grab (tires squeaked) but then they were fine for the six mile trip home. Every time this has happened the trailer was parked in dusty conditions so there is a correlation there but I have no idea the cause. Playing with the pin shows correlation but still no idea on cause. The interval the trailer was parked ranged from one night to four months. I am going to talk to my trailer guy again but wanted to get some opinions before I do. Thanks in advance.
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Old 05-21-2014, 09:09 AM   #2
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Two things to check

My first thought for probable cause 1s:

The brakes on the trailer are incorrectly wired to the brake lights. The process of getting the older AS umbilical wires tied into the proper pin position of modern tow vehicle 7 pin hookups is well documented. When I picked up the '78 Sovereign in Ohio I spent a rainy and cold afternoon in a Walmart parking lot attempting to sort out the wiring issues. The wiring difficulties did not help my attitude during the tow from Ohio to Texas - took one day longer than planned.

Can you check for both voltage and amperage in the umbilical brake line circuit while someone applies the brakes in the tow vehicle?
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Old 05-21-2014, 09:21 AM   #3
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Another theory - something is shorting to your brake wire. For example, if the +12 volt constant wire was occasionally hitting your brake's wire, the brakes would come on at full power. First place to look would be in the 7 pin connector...beyond that it'd be tracing wires.
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Old 05-21-2014, 05:12 PM   #4
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I have seen drums that get rustly and shoes (or may be this case is a magnet) get hung up on the drum because of the rust.

Just a shot in the dark, however I have seen this on the rear drum brakes of some cars that sat for a long time. The rust took some time to wear off after the brakes were used and it was inconsistant in at least one application.

Again just a guess and may be not the cause.

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Old 05-21-2014, 05:48 PM   #5
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Brakes will grab after sitting for a prolonged period of time. This generally is on the first few application and do to rust on the drum face. Not your problem.

Does your brake controller have an amp read out and if so what amperage is displayed when the brakes grab? If the amperage is high at that point the problem is in the controller. If the amperage is normal for the pressure you just used to apply the brakes than the problem is rearward.

The spacing between terminals in both the receptacle and plug is minimal so I would open both checking for a possible short between wires. I like to soldier in place and then tape between each connector to ensure against problems like this.

If the controller, receptacle and plug check out OK has anyone checked the adjustment of the brakes. I have seen brakes using a single return spring on the shoes hang up and not release both shoes from time to time.
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Old 05-22-2014, 07:41 AM   #6
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1964 24' Tradewind
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I am getting some good feed back here. Thanks.

I do not think it is rust or dust on the brake drums. I have experienced that on vehicles and this is more pronounced. This is more like the brakes have been completely engaged. When I take my foot off they release normally. The intermittent part I would think implies a short or something loose.

There is no voltage reading on the controller unfortunately. Do controllers go intermittently bad or do they just fail? Looks like maybe my best bet is to dig into the 7 pin or have the guy who wired it take a look. I am assuming the female part of the connection would be less likely because it is a new vehicle. Anyone have additional thoughts? Electronics are not my strongest area.
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Old 05-22-2014, 07:48 AM   #7
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Have seen brakes that grab the first time or two used whenstarting out. I just thought it was dampness, always worked okay after the first few tries. Does your problem persist or is it only once or twice.? I do not think this is your problem but, who knows? Jim
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Old 05-22-2014, 08:57 AM   #8
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If the brakes ARE GRABBING while you have your foot on the brakes and RELEASING when you let up I think we can assume the problem is not in the wiring of the plugs or in the wiring of the trailer. I would look closely at the controller since that is about the only source of current of that magnitude and controllable by the brake pedal.

A short in the plugs or trailer wiring would not be effected by the brake pedal.

If you can get another controller for a trial I would wire it in and try that.
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Old 05-22-2014, 09:11 AM   #9
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Worn magnets can cause problems as well as brakes being adjusted too tight. I had to back off on the adjustment on a couple of my wheels. Also if you have any grease on the drums they will grab. Standard brake controllers are on-off with a bit of delay before full application. The speed you are going also affects how much braking you get. Trailer brakes seem to work much better at slow speeds than at high speeds. It maybe you need to back off the adjusters on the offending wheels or back off the voltage on the controller. If you back all the way off the controller voltage and the brakes are still locking then they are wired to the brake lights or something. Worn magnets can make the locking problem worse.

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Old 05-22-2014, 11:41 AM   #10
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1964 24' Tradewind
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Quote:
Originally Posted by HowieE View Post
If the brakes ARE GRABBING while you have your foot on the brakes and RELEASING when you let up I think we can assume the problem is not in the wiring of the plugs or in the wiring of the trailer. I would look closely at the controller since that is about the only source of current of that magnitude and controllable by the brake pedal.

A short in the plugs or trailer wiring would not be effected by the brake pedal.

If you can get another controller for a trial I would wire it in and try that.
The breaks only grab when my foot is on the brake. When I take my foot off the break there is no drag. Also I should have said it is like I have slammed on the brakes. The thing that had me steering away from the controller was that it did not happen every time. Also while it is happening adjusting the gain had no effect. I guess I will try to borrow a controller and see what happens. If I need to buy a new one, any recommendations?
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Old 05-22-2014, 12:01 PM   #11
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Some brake controllers are sensitive to tilt. The more the controller is tilted from level, the more "grab." Did the controller get knocked into a steeper mounting tilt when your problem began?
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Old 05-22-2014, 12:46 PM   #12
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Quote:
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The breaks only grab when my foot is on the brake. When I take my foot off the break there is no drag. Also I should have said it is like I have slammed on the brakes.
Yeah, then I'm leaning toward some issue with the controller as well. I used a Tekonsha Prodigy when I had the B190 with the tow dolly and I really liked it.
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Old 05-22-2014, 01:06 PM   #13
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Measure the voltage at the plug and see if it changes based on the gain setting. Just blindly replacing stuff is not the answer. You might go through half a dozen controllers before you find out it is not wired correctly. Also check voltages using the manual lever and by pressing the brake.

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Old 05-22-2014, 01:26 PM   #14
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Seems like your brake light wire is powering your brake magnets. Full on or off.
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