Electric and hydraulic trailer brakes stop the trailer in different ways and use different parts. Before you order anything, find out which system you have. It takes about five minutes and saves a second trip to the store.
How electric brakes work
Electric brakes are controlled from the cab. A brake controller in the tow vehicle sends power through the 7-way plug to a magnet inside each brake. The magnet grabs the spinning drum, which pulls the brake shoes outward and slows the wheel. You can set how hard the trailer brakes, and most controllers have a manual lever for stopping the trailer on its own.
The downside is water. Magnets and wiring don’t like being dunked, especially in salt water, so they wear faster on boat trailers.
How hydraulic surge brakes work
Surge brakes don’t need a controller. When the truck slows down, the trailer pushes forward against the hitch and compresses an actuator at the coupler. That pushes brake fluid down the lines to the wheel cylinders or calipers. The harder you stop, the harder the trailer brakes.
Because they work without electronics, surge brakes are common on boat trailers. They need a way to stay off when you back up, either a solenoid wired to the reverse lights or a manual lockout pin, or the brakes will fight you in reverse.
Electric over hydraulic
There’s a third option on heavier trailers: an electric pump on the trailer that’s driven by your brake controller and pushes fluid to hydraulic disc brakes. You get in-cab control with brakes that handle water better.
How to tell which one you have
Look behind a wheel at the backing plate. Two wires going into it means electric brakes.
A metal brake line or rubber hose going to the backing plate or a caliper means hydraulic brakes.
Check the tongue. A large housing at the coupler with a fluid reservoir is a surge actuator.
A small pump unit mounted on the tongue or frame means electric over hydraulic.
Check the plug. A 7-way plug often, but not always, means electric brakes. A 4-way flat plug can’t run electric brakes at all.
Side by side
Electric | Hydraulic surge | |
|---|---|---|
Needs a controller in the truck | Yes | No |
Control from the cab | Yes | No |
Backing up | No issue | Needs a reverse lockout |
Launching in salt water | Parts wear faster | Better suited |
Typical plug | 7-way | 4-way or 5-way |
Parts to match
Electric brakes
Match the brake size, usually stamped on the backing plate (10″ x 2-1/4″ and 12″ x 2″ are the most common), and note left or right side. Magnets and shoes are also sold separately.
Hydraulic brakes
Note whether you have drum or disc brakes, the actuator make and capacity, and the brake line fittings. Use the brake fluid your actuator maker recommends.
Shop tip
Brakes work as a set. Replace both sides of an axle together so the trailer stops straight instead of pulling to one side.
Can you switch systems?
Yes, but it’s more than a brake swap. Going from surge to electric means new brakes, wiring and a controller in your truck; going the other way means an actuator, lines and possibly new hubs. Talk to us first and we’ll price both options.
Get the part or the repair
Shop online for local pickup, or bring the old part to our Port St. Lucie store at 496 SW Voltair Terrace and we’ll help you match it. Not comfortable doing the job yourself? Request a repair and we’ll take care of it, or call us on 772-924-7299.
Guides are general advice. Trailers vary, so check your trailer’s labels and manuals, or ask us before you order.
