What Causes Electric Trailer Brakes to Lock Up When Applied?

by K.K. Lowell

How Electric Trailer Brakes Work

Electric trailer brakes work because an electromagnet attached to the end of an arm inside the brake drum is attracted to the spinning brake drum when current from the tow vehicle is supplied to the brake. This arm is linked to the brake shoes, which are extended to contact the brake drum when the magnet tries to grab onto it. The more current supplied, the stronger the magnetic attraction and the harder the shoes are pressed against the brake drum.

Why Electric Trailer Brakes Lock Up

The causes of electric trailer brakes locking up are few: 1) Brake controller adjusted incorrectly for the load; 2) Brake controller failure; 3) Grease on the brake shoes; 4) Poorly adjusted brake shoes; 5) Broken brake shoe. When brakes lock up due to controller issues. it is generally both wheels that lock up. Try reducing the brake voltage by adjusting the knobs on the controller to see if the problem goes away. Most controllers need to be manually adjusted to work correctly when the load is removed from the trailer. The easiest way to check for a controller that has failed and cannot be properly adjusted is to try the trailer on another tow vehicle. If the brakes do not lock up when towed with another vehicle, you should replace the brake controller in the first tow vehicle. If the problem is in only one wheel, jack the trailer up and remove the wheel and brake drum. Check for grease on the brake shoes or broken pieces of brake shoe or spring that could cause a mechanical lockup. If grease is found, replace the grease seal. If brake shoes or springs are broken or excessively worn, replacement on both sides of the trailer is mandated. If no other problem is found, the electric trailer brakes may be locking up due to incorrect brake adjustment. Try adjusting the brakes to eliminate the locking problem.

Preventing Electric Brake Lockup

Because the most common cause for electric trailer brakes to lock up is the inexperience of the driver, the easiest way to avoid problems in the future is becoming familiar with and using the adjustments on the brake controller. Experiment with the settings of the controller while towing the trailer in a parking lot or low-traffic street. Brake lockup problems caused by mechanical issues can be avoided in the future by following a regular maintenance schedule.

About the Author

K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.