Trailer Brake Bleeding Instructions

Manual Bleeding of the UFP Trailer Brake System

If you are not skilled in performing the following procedures, have a qualified service shop do the job.  Check that all hydraulic fittings are secure. Read and understand all instructions before starting. Two people are required for manual bleeding.

1. Remove the master cylinder reservoir plug and fill the reservoir with brake fluid. Use either DOT 3 or DOT 4 automotive brake fluid. Follow instructions on brake fluid container. Avoid shaking brake fluid container and pour liquid slowly to minimize air entrapment. Let fluid in reservoir stand until completely free of air bubbles.
2. IMPORTANT: Before bleeding brake lines, bleed the actuator master cylinder. Insert a screw driver through the hole in the bottom of the inner member and use short strokes to pry on push rod (while holding safety release bracket up) until no air bubbles are seen coming from small orifice hole in the bottom of the master cylinder reservoir.
3. Start bleeding procedure on the brake furthest from the master cylinder.
4. At the brake assembly, connect a transparent bleeder hose to bleed screw fitting on wheel cylinder and submerge free end into a container partially filled with brake fluid. Do not reuse this fluid.
5. The first person strokes the pushrod slowly while holding safety release bracket up. The second person opens the bleed screw fitting. He then closes the bleed screw fitting BEFORE the first person SLOWLY releases the pushrod. Repeat this procedure until the fluid expelled from the bleeder hose is free of air bubbles. Remember to always tighten the bleeder screw before releasing pushrod. During this process, the master cylinder reservoir fluid level must be maintained at no less than 1/2 full.
6. Repeat steps 4 and 5 for the other brake and the brakes on the front axle, if equipped with tandem brake axles.
7. If the installation is tandem axle with brakes on both axles, repeat bleeding procedure on rear axle brakes for the second time to assure purging of all air in the system.
8. As a final check after bleeding is completed, stroke pushrod and check to be sure brake system is pressurized by attempting to rotate a tire.
9. Push up on the safety release bracket to ensure that pushrod is in the released position.
10. After bleeding has been completed, re-check fluid level in master cylinder. Fill the master cylinder reservoir to the indicator on reservoir plug. Do not overfill.