trailer brakes locking up

[Craig M]

Have a 3 axle car type pull trailer with brakes on two of the 3 axles. Brakes are the magnetic type. Typically pull the trailer with my dually. Dually has brake controler. When applying brakes (even slowly) trailer tires tend to lock up. Have tryed using the sensitivity switch on the controler, does not appear to help. Situation is usually worse with no load on the trailer than when heavily loaded. Had the magnets and all checked out at a trailer repair shop a while back. Noticed the problem a bit then and should have gone bck to them. Any ideas?

[chipper]

Your controller is probably either defective or misadjusted. Get the setup instructions for it & adjust both the GAIN & SENSITIVITY per the instructions. If this doesn't cure the problem you probably have a defective controller.

[a5150nut]

Since your duelly is older you probablty have an older style controler. They used to use a resistor under the hood. It looked like a loop of coiled wire mounted on a board. Moving the contact up or down the coil changed the resistance and made the brakes softer.

[HowieE]

There is no controller made that will correctly apply the trailer brakes, with just one setting, over a range of load you are discribing.

I would take the truck and trailer out to an open area or road that you can do some testing on and set up the controller, per the manufacutres instructions, with the trailer empty and record that setting. Then load the trailer and go back and set the controller up with a load.

You will have to change between these settings depending on if the trailer is loaded or not.

Most manufactures have you go about 25 mph and hit the "manual" controll hard. If the brakes lock under this condition repeat the test with the controller set a little less and repeat this test until the brake do not lock. This setting, just below lockup, is the correct setting for that load. Repeat this procedure for each load range you intend to tow and record each setting for future trips.

[2jranch]

Check for bad wire on the trailer, could be shorting out. A comon problem with campers etc. The wire they use is really cheap and the plastic coating cracks and a short will develop causing the brake to lock up every time energized.

[cos]

Craig.... HowieE nailed it right on the head. Keep in mind that electric brakes are not perfect....