The Open and Closed about Trailer Brakes
by arlyn stewart

My trailer was only three years old when the brakes failed.  Wheel cylinders were leaking and sticking with  the right front axle running hotter than normal due to the brake lining holding some engagement to the drum.  It was time to rebuild but first I wanted to know why the system failed so quickly.

What was the cause?  The simple answer is rust.   Brake actuators and wheel cylinders are cast iron.  A little rust outside is no big deal, but inside a little rust causes problems.  Rust is abrasive to the rubber cups, contributes drag to the piston and deteriorates the smooth bore of the cylinder necessary to sealing the fluid from leaking.

The rust is caused by water within the system, carried there by the brake fluid.  Normal brake fluid attracts water like a sponge from simple exposure to the air.  This is why autos and trucks have closed brake systems.  In those systems, the reservoir is provided with a badder which separates fresh intake air from the brake fluid.  Boat trailers with hydraulic surge brakes don't have this isolation but they should. Probably no other brake system suffers such exposure.  The actuator sets for long periods exposed to the elements and often gets submerged  during lauch or retrieve.   Even during normal service when the actuator is activated, fresh air is exposed to the fluid.

In the absence of a closed system, the alternative is to use a brake fluid that doesn't attract moisture.  Fortunately, such a fluid exist in the synthetic Dot 5 brake fluid.  Unfortunately, the fluid is expensive.  It is however cost effective when one considers rebuilding cost.

After rebuilding, my brakes are still working great five years later and the fluid continues to be clear meaning that it is not contaminated by rust.