This post was written by daves on February 18, 2009
There are two basic types of hydraulic trailer brakes typically seen on trailers: Drum brakes and Disc brakes. Drum brakes are an older style and use a hydraulically actuated wheel cylinder to force a pair of spring loaded brake “shoes” against the internal braking surface of brake drum, which also acts as the hub.
Disc brakes use a hydraulic actuation of a piston in the caliper to force the pads to close (pinch) both sides of the rotor. This is a newer design found on most modern automobiles.
Disc brakes have a few advantages over drum.
1) Better stopping power
2) No adjustment necessary to compensate for shoe wear
3) Easy pad replacement
4) Less complicated – no springs
5) For boat trailers, reduced incidence of corrosion
Disc brakes come in two basic designs: Vented and Non-vented. Vented rotors are preferred because they tend to dissipate heat better than non-vented rotors, minimizing a main cause for failure.
For boat trailers, corrosion caused by immersion in fresh or salt water is always a main concern. The salt water can also cause problems when salt crystallizes in the moving parts of the caliper and on the caliper pins. The disc brakes available today, come in either powder coated for standard use, silver cadmium plated for standard salt-water use or stainless steel for extended saltwater use.
To begin the conversion from drum to disc brakes, it is best to start at the front of the trailer. The Hydraulic actuator, (surge or electric/ hydraulic) will need to be either modified or changed out to one that is designed for disc brakes. The disc brake actuator will have an outlet brass fitting with a larger aperture (5/32”) and the check valve found in the drum brake actuator will be absent. Disc brakes require more flow of brake fluid than drum brakes.
Since disc brakes are not designed with the (free-backing) feature, a method to lock out the brake lines will be required. This can be accomplished by installing either an electric lockout solenoid or a mechanical manual ball valve placed in the brake line.
The disc brake calipers require a flexible brake line leading into the piston to work properly. Inspect your brake line and install if necessary.
Safely jack up and block your trailer. Remove the tire / rim assembly. Remove the old brake drum and the brake assembly. The brake assembly is fastened to the axle brake flange with 4 or 5 bolts.
The new disc brake assembly will have a bracket, caliper, rotor and mounting hardware included. General steps to make the conversion are as follows.
Step 1: mount the bracket to the axle flange.
Step 2: prepare and slide the rotor on to the axle spindle and lock in place. Follow standard practice to set the bearings.
Step 3: The caliper will then sit on the rotor and be fastened to the bracket with “slider pins”. Read your assembly instructions before beginning the installation.