How to Bleed Hydraulic Surge Trailer Brakes

Published 10/19/2012

Question:

Im having the fix a broken brake line. How do I pump the system to bleed the line?

asked by: Robert W

Expert Reply:

There are a couple of ways you can bleed a trailer brake system. Titan offers the following instructions, which I have also linked for you, on bleeding the brakes:

Remove the master cylinder cap and fill the reservoir to three quarters full with DOT-3 brake fluid. DO NOT allow brake fluid to contact painted surfaces since it will damage the finish. Wipe up any spills immediately and wash the area with water.

If you choose to manually bleed the system, an assistant makes the job easier. Disconnect the trailer from the tow vehicle and hook the safety chains (NOT the actuator breakaway cable) together to form a loop. The loop should be centered below the actuators coupler.

Place a sturdy board such as a 2 x 4 into the safety chain loop below the coupler. The board should be four feet long or more so it will extend well above the actuator. Position the board to press against the front end of the actuator’s coupler and use it to force the coupler case into the actuators outer housing. This pumps the brake fluid into the trailer braking system. Manually pull the coupler case back to fully extended position and repeat the process.

When the air bubbling stops inside the master cylinder, install a bleeder hose on the bleeder screw of the first wheel cylinder to be bled. Start with the rear axle on tandem axle trailers. Submerge the other end of the hose in a glass container of brake fluid so that air bubbles can be observed. Open the bleeder screw one turn before pushing the coupler case in. When the coupler is pushed completely in, the bleeder screw should be closed to prevent air from being pulled back into the system. Air trapped in the brake lines will greatly reduce your braking efficiency. Repeat this process until no more bubbles are released with each stroke. Be sure to close the bleeder screw securely.

Repeat the bleeding operation at each wheel cylinder. During the bleeding process, replenish the brake fluid so the level does not fall below half full level in the master cylinder reservoir. When bleeding is complete, fill the reservoir to within 3/8 inches of the top. Install the filler cap securely.

There are also vacuum types of systems that you could use but doing it manually is what most people do. I have also included a link to a video that should help.

expert reply by: Michael H