surge brake troubleshooting
Don’t attempt working on your brakes if you aren’t experienced with brake systems. These troubleshooting tips assume that a person is familiar & equipped with jacking & supporting safety stands, brake tools, seal & bearing inspection techniques, shoe, drum, rotor inspections, & knows how to adjust, fill & bleed brakes.
AUTOMOTIVE HYDRAULIC BRAKE SYSTEMS
The car that you drive has hydraulic brakes. The brakes in your car consist of a “pump” (master cylinder) that you operate with your foot (brake pedal) connected by brake line tubing to a hydraulic cylinder (wheel cylinder) that pushes the brake shoes against the brake drum or disc brake caliper & rotor. The harder you push the pump with your foot, the more pressure you generate, thus the harder the brakes shoes are forced against the rotor or drum to stop you. These systems use brake fluid to do the work. If you would like to look at specific surge brake related parts, please click here to visit our online parts section.
TRAILER SURGE BRAKE HYDRAULIC SYSTEMS
Typical Surge Brake Actuator
Surge Brakes on a trailer are also hydraulic brakes and work very much the same-with one difference. In a trailer surge brake system, the “pump” is located on the trailer-as part of the hitch assembly. This special sliding hitch assembly is called a surge brake actuator. It has a master cylinder built into it, but instead of using your foot to operate it, it uses the weight & the momentum of the trailer to do the pumping.
Above is a rear view showing a Master Cylinder & Outlet Port (top). This heavy duty unit shows that shock absorbers on the bottom prevent the slide from jerking front to back during stop & go movements.
Emergency Breakaway Systems
Federal law requires all trailers to have a “breakaway” system. If your trailer ever came loose from the tow vehicle while underway, the breakaway system will activate the brakes on the trailer to slow it down & stop it-hopefully preventing an accident. The breakaway system usually consists of a cable or chain that is attached to the tow vehicle on one end, & a lever/latch assembly on the trailer surge actuator. Since the chain or cable is attached to the tow vehicle, if the trailer come loose from the truck the cable pulls the lever energizing the trailer brakes. A latch mechanism keeps the lever in the energized mode even if the breakaway chain or cable is ripped away by the separation of the truck & trailer. The lever mechanically pushes the master cylinder piston to generate emergency brake fluid pressure & the latch assures that the pressure is maintained until the latch is disengaged manually by using tools. The breakaway system can be helpful in performing tests & even for bleeding the brakes, so understand it & use it to help you keep your brakes in top shape. If you would like to look at specific surge brake related parts, please click here to visit our online parts section. We also feature a number of emergency breakaway parts for trailers.
(Shown) Two styles of breakaway systems
TYPICAL SURGE BRAKE TROUBLESHOOTING PROBLEMS:
"Brakes Don’t Seem to Work At All"
First, do a test to see what’s going on. Find the breakaway chain or cable & pull it until it latches in the locked position. An easy way to do this is to find something that you can use as a lever. (See photo below)
Jack up all the tires & wheels that have brakes. Manually rotate the tires/wheels using your hands in the forward travel direction & see if they lock up. Check each wheel that has brakes, as it is possible for some of the brakes to work, but not all of them.
Important: The surge actuator slide must be pulled & pushed (full stroke) to create pressure & bleed air from system when making repairs or tests. The slide will offer resistance due to the orifice & shock absorbers, so expect to stroke it with effort. If you would like to look at specific surge brake related parts, please click here to visit our online parts section.
Got Brake Fluid?
If none of the brakes work, remove the master cylinder cap & look inside to see if there is any brake fluid in the reservoir. If not, we recommend you rebuild or replace the master cylinder & wheel cylinders. The absence of brake fluid-especially for any length of time allows rust to form in the entire system-including the steel brake line tubing. Rust is the enemy as it creates rough surfaces inside the wheel and master cylinder bores destroying the piston seals. Rust particles will also flow around with the brake fluid & eventually will plug up the orifice (see orifice photo). In some cases it is possible to hone the cylinder bores & replace the seals to rebuild them, but usually the bores are pitted beyond repair. Missing brake fluid means you have a leak. You must find the source of the leak & fix it. Don’t merely add brake fluid & go back on the road!
Inspect The Brakes at the Wheel
If brake fluid exists in the system, a process of elimination is needed to find why the brakes aren’t working. It is possible the brake shoes are worn completely out, or the drum brakes are greatly out of adjustment. We recommend you remove the brake drum & visually inspect the shoe linings. While the brake drum is off, have an assistant manually operate the brake system using the breakaway lever. Have them work the surge actuator from “off to on” & closely watch the wheel cylinder to see if the push rod is moving in & out. If not, the wheel cylinder may be frozen, or the master cylinder is not pumping, or the orifice may be clogged. Important: the surge actuator slide must be pulled & pushed (full stroke) to create pressure & bleed air from system when making repairs or tests. The slide will offer resistance due to the orifice and shock absorbers, so expect to stroke it with effort.
Inspect/Test the Master Cylinder
To test the master cylinder, remove the brake line or hose from the rear of the master cylinder located on the surge actuator. DO NOT remove the orifice fitting that the hose or brake line attaches to. This orifice is very, very small-perhaps as small as the diameter of one strand of hair on your head & can easily clog with debris. Engage the master cylinder using the lever to see if it forces a fine stream of brake fluid thru the orifice fitting. If not, remove the orifice fitting & then test it again by engaging the master cylinder. If it now pumps fluid, hold the orifice up to a strong source of light and see if you can see through it. If not, it is clogged & is preventing the brake fluid from reaching the wheel cylinders. Unclog or replace the orifice, reinstall it in the master cylinder, then test again. (If the clog is on the master cylinder side of the orifice fitting, it prevents pressurized brake fluid from operating the brakes. If the clog is on the wheel cylinder side of the orifice fitting, it creates problems when the brakes try to release because it prevents the flow of brake fluid back to the master cylinder reservoir). If the master cylinder won’t pump in all of these tests, it needs replacement. If the master cylinder does pump, proceed to the next step. (Note: it is possible for a master cylinder to pump fluid at a low pressure, but could have internal piston seal leakage that prevents it from building up adequate pressure to operate the trailer brakes.)
Test the Brake Line for Blockage
Remove the brake line from a wheel cylinder & have an assistant pump the master cylinder using the lever. Look at the end of the brake line you just disconnected. If brake fluid is being pumped thru the line, the master cylinder, orifice & brake line seem to be working, so assume the wheel cylinder(s) should be suspect at this point.
Bad Wheel Cylinder?
If you have proven the master cylinder is working, the orifice isn’t clogged, and the brake tubing is clear, the wheel cylinder should operate when the master cylinder is engaged using the lever. If it doesn’t, the wheel cylinder most likely has a frozen piston. Although you really can’t bench test the wheel cylinder, you can peel back & remove the rubber boot to look for rust or corrosion that would prove a stuck piston. If you have a stuck piston, replace the wheel cylinder with a new one. It’s a very inexpensive part.
"Brakes Work on Some Wheels, But Not on Others"
If the brakes work on even one wheel, it would indicate the master cylinder & orifice are okay. The wheels that don’t work will have one of the following problems that you’ve already learned how to test and fix: