Key Differences Between Disc Brake and Drum Brake Trailer Coupler and Brake Actuators

Published 06/27/2011

Question:

Hello, I have a dual axle trailer with Kodiak disc brakes on all four wheels and an Attwood coupler. When I cap the brake lines, the push rod spring will bottom out at about 1/2 throw and provide a hard hydraulic stop. Connected to the cylinders, however, the spring BEGINS compressing at about 1/2 throw and I can push all the way to the mechanical limit of the coupler without much difficulty using a 1 bar. I dont believe that this is providing adequate braking, as in reverse on dirt, one axle will lock but the other will roll, with the coupler at the mechanical limit. With a boat aboard the coupler will surely be banging on every stop. I thought I had the correct coupler...is there any way to verify that I have a disc coupler and not a drum coupler? How about the push rods and springdisc and drum types or all the same?

asked by: Aaron S

Expert Reply:

Drum brake actuators and disc brake actuators use different master cylinders. A disc brake actuator producer a higher psi than a drum brake actuator so the fittings will be a little different as well. The drum brake master cylinder will have a check valve in it that reduces the amount of psi the system puts out. The disc brake models do not have this valve because more pressure is needed to actuate disc brakes

The problem could be air in the lines and/or pistons in the calipers that are not properly adjusted or that are not operating correctly. The first thing I would do is bleed the brake system. I have included a link to a video that shows how to bleed trailer brakes.

The two different types of couplers do share some of the same parts. The push rod and shock can be the same between models.

expert reply by: Michael H