Difference Between Single, Dual and Free Backing Servo Brake Assemblies

Updated 05/03/2017 | Published 05/01/2017

Question:

Just a few questions. Looking to replace my trailer brakes on my boat trailer. They are hydraulic drum brakes. I believe 12inch by 2 inch wide. I see there are a few terms I am not exactly sure what there talking about. Dual servo? s single servo.. Free backing?? Any help would be great. Its a triple axle trailer with drum brakes on 2 of the 3 axles. I travel alot with it and the boat and trailer together weigh almost 11k lbs. Any suggestions on what to use??

asked by: Jim P

Helpful Expert Reply:

The biggest difference between the servo styles that you'll notice is between free backing plates and the others. The free-backing plates will allow your trailer to back up without having the brakes lock up. With surge brakes typically when you go to reverse the trailer it pressurizes the brake system which locks the wheels up. Free backing setups are designed to allow the pressure to build but not activate the shoes of the assembly so the trailer can back up.

Some surge brake trailers have reverse lock out systems built into them so the free backing plates aren't needed. The difference between single and dual servo is that for dual servo the wheel cylinder pushes on both shoes instead of just one. Typically this is seen on the higher capacity brake assemblies.

I attached a link to a page that has all of the hydraulic drum assemblies we offer.

expert reply by: Jameson C