UFP DISC BRAKE SYSTEM
BLEEDING INSTRUCTIONS
1. To facilitate bleeding of the trailer’s disc brake system it is helpful if the actuator is lower than the disc brake calipers. It is easier to push the air in the system up and out rather than trying to force the air down. It is also important that any rubber flexible brake lines are routed such that the line does not slope up before sloping down which would create a pocket where air can get trapped.
2. A single person can accomplish bleeding the brake system if you use a power bleeder and UFP’s bleeder clamp assembly. The pressure in the power bleeder should not exceed 18 psi. Exceeding this pressure will damage the diaphragm in the master cylinder reservoir causing it to leak. Always use clean DOT 3-brake fluid. Never reuse old fluid, as it will contain contaminants and water moisture. Always seal fluid containers as soon as possible as brake fluid is hygroscopic and readily absorbs moisture.
3. Attach bleeder clamp assembly to actuator. Make sure clamp assembly is adjusted properly. If clamp is too tight it will crush and damage the master cylinder reservoir cover plate. If the clamp is too loose it will not make a good seal and will leak fluid when bleeding the brake system.
4. Turn on valve at pressure bleeder and check for leaks where bleeder head enters master cylinder reservoir.
5. Start bleeding with the brake at the farthest end of the brake line. If trailer has tandem brake axles, start with the brake at the farthest end of the brake line on the rear axle first.
6. At the disc brake caliper assembly, connect a clear bleeder hose to the bleeder screw located on top of caliper body and place free end of hose in a suitable container. DO NOT REUSE THIS FLUID.
7. Loosen bleeder screw one turn. When no air bubbles are visible coming out of bleeder screw for at least three seconds, close bleeder screw securely and remove bleeder hose.
8. Repeat steps 6 and 7 above on brake on the opposite side of axle and then on front axle if so equipped.
9. If installation is tandem axle with brakes on both axles, repeat bleeding procedure on the rear axle brakes for the second time to assure positive purging of all air from system.
10. Close valve at bleeder head. Relieve pressure in bleeder pot. Slowly remove bleeder clamp assembly.
11. Check fluid level. Not enough fluid in the reservoir will cause the reservoir to run dry as the disc brake pads wear. Too much fluid will cause a overflow situation when the solenoid valve is energized during backing up. Proper fluid level is when the fluid in the reservoir just touches the end of the dip stick on the fill plug when it is inserted fully into the fill hole.
12. Wipe off any brake fluid that may have spilled on the top of the reservoir or actuator body.
13. Proper bleeding of brake system can be checked by performing one of the following procedures;
(1) Compress actuator and verifying brake rotor can not be rotated
(2) Stroke pushrod assembly with a screwdriver and verifying brake rotor can not be rotated (Note: If using this procedure, make sure you push up on the pushrod release bracket afterward to fully release the brakes).
(3) Back up the trailer, without the energizing the solenoid valve, to verify brakes are working.
(4) Pull trailer forward and stop suddenly, pin on side of actuator should not travel more than ½ way in slot for single brake axle or ¾ way in slot for tandem brake axles.
14. If brakes are not working properly, there is still air in the brake system and the system will have to be re-bled.
15. Check for leaks at all fittings and connections and tighten or correct as necessary.
UFP does not consider itself an expert on bleeding trailer brake systems for mass production. This information is provided solely as a convenience to our customers. We would appreciate any suggestions that would improve the accuracy, quality or efficiency of this procedure. For suggestions, questions or comments regarding this procedure please call our Customer Service Department at 800-854-1905.