Maintaining and Repairing Your Car Trailer Brakes

General Car Repairs

By Rodney (Mechanics)

When you’re towing a trailer with a heavy tow vehicle, like over 3,000 pounds, you’ll likely need trailer brakes. Some places even require brakes on trailers as light as 1,000 pounds. If your trailer has two axles and weighs more than 5,000 pounds, both axles might need brakes.

Why are trailer brakes so important? Well, imagine your trailer is heavier than your car or truck. That could be dangerous! Having brakes on the trailer helps keep things stable when you hit the brakes hard, reducing the chance of the trailer swinging out of control.

People often don’t think about trailer brakes until something goes wrong, so it’s crucial to check them often and fix any issues that come up.

Trailer brakes are similar to those in cars and light trucks, needing similar upkeep. Rust is a big worry, especially for boat trailers, since brakes can get wet during loading and unloading, causing them to stick. Saltwater is particularly tough on brakes, often leading to necessary repairs or replacements after a few seasons of boating. Wheel bearings are also at risk from water and rust and need regular cleaning, greasing, and adjustment to avoid failure.

Electric Trailer Brake Kit Part

Overview of Car Trailer Brake Types

Trailer brakes come in two main types: electric and surge. Electric brakes get triggered either by connecting to the tow vehicle’s brake pedal or through an adjustable dash-mounted inertia switch in the vehicle or on the trailer itself. When you apply the brakes, an electric current powers up a magnet in each brake, which then moves a lever to engage the brakes. When you release the brake pedal or start moving again, the power to the magnet stops, and the brakes let go. Plus, you can adjust the controller to handle different loads on the trailer.

Surge brakes work automatically without needing an electrical connection between the tow vehicle and trailer (except for the lights). The surge coupler, which sits on the trailer’s tongue, contains a linkage linked to a hydraulic master cylinder. When the tow vehicle brakes, the trailer’s forward momentum pushes on the surge coupler, causing it to slide back and apply pressure to the master cylinder piston rod.

The pressure on the trailer brakes is proportional to the force the trailer tongue exerts on the trailer hitch of the tow vehicle. The harder the deceleration, the more hydraulic pressure goes to the trailer brakes. After stopping and starting again, the forward pull on the surge coupler releases pressure on the master cylinder, freeing the trailer brakes.

While surge brakes are simple, they can’t distinguish between regular braking and backing up. So, they need either a mechanism to release the brakes while reversing or a reverse solenoid connected to the tow vehicle’s backup lights to release brake pressure during backing up.

Surge brakes are popular for boat trailers as they endure well in wet environments where electrical brakes struggle. They’re also common on rental trailers since they don’t need extensive electrical setups apart from trailer lights. Yet, in certain states, surge brakes may not be considered adequate for heavier trailers or commercial purposes, such as hauling construction equipment. For such cases, electric brakes are mandatory, requiring the tow vehicle to have a controller to manage the trailer brakes.

Federal law says that trailers with brakes must have a safety system. If the trailer comes loose from the vehicle, this system automatically puts on the brakes. For trailers with electric brakes, it involves a backup battery and a switch connected to the towing vehicle. With surge brake systems, there’s usually a cable or chain attached to the towing vehicle to activate the brakes if needed.

Most trailers use drum brakes, but some have disc brakes. Drum brakes may have a single-piston “uniservo” wheel cylinder or a dual-piston “duoservo” brake. Boat trailers often feature galvanized springs and hardware to resist corrosion better. Additionally, their brake shoes may be riveted rather than bonded to prevent water-logged linings from detaching.

Drum brakes can work with electric or surge/hydraulic systems, but electric drum brakes must have a flat contact surface for the magnet. It’s important not to use replacement drums designed solely for hydraulic systems on trailers with electric brakes.

The number of axles and brakes required on a trailer varies based on weight capacity and state regulations. Typically, Typically, on 2,000- to 2,500-lb. axles use 7-inch brakes, and 12-inch brakes on heavier axles. If a tandem-axle trailer has only one set of brakes, they’re usually on the front axle.

How to Properly Inspect Your Trailer Brakes

To ensure safe driving, it’s important to check your brakes thoroughly. When your vehicle is moving, the brakes should release completely, and when you brake, they should engage evenly and effectively.

Inspect the condition of various brake components such as drums, shoes, return springs, and hardware. Replace heavily corroded parts and ensure adjusters turn smoothly. If shoes or drums are too worn, replace them promptly.

For vehicles with disc brake systems, examine rotor thickness, condition, and runout. Replace warped, excessively worn, or cracked rotors. Evaluate pad thickness and condition, replacing worn-out or damaged pads.

For hydraulic brake systems, make sure to inspect for any fluid leaks in the wheel cylinders, brake lines, and the master cylinder. Inspect brake fluid for rust, sediment, or water contamination using test strips for accurate assessment.

For electric brake systems, assess wiring, connectors (especially the main trailer connector), magnets, and battery condition. Ensure the emergency battery is fully charged and securely mounted.

To test surge/hydraulic brake operation, lift trailer wheels and confirm they spin freely by hand. Dragging may indicate issues with wheel cylinders, corroded parts, or misadjusted brakes. Press down on the surge coupler to activate the brakes evenly for a few seconds, and inspect for any leaks or problems with the internal master cylinder.

If brakes aren’t functioning, check master cylinder fluid level and bleed lines or adjust drums if necessary. If issues persist, inspect for obstructions in brake lines or consider replacing the master cylinder.

Take a short test drive to verify proper brake operation and adjustment. If the coupler produces excessive noise when brakes are applied, adjust drums to reduce shoe clearance and improve performance.

Electric Trailer Brake Systems for Cars and Trucks

To check electric brake systems, activate the emergency stop to see if it slows the wheels, or power the trailer brake control circuit with a 12-volt battery (use protected jumper wires). If brakes don’t work, inspect wiring, trailer’s circuit breaker or fuse, ground connections, and magnets.

Even if the brakes seem fine, the only surefire way to know if they’re adjusted correctly is to take the trailer for a test drive behind a vehicle.

Electric Trailer Brake Kit Installation

Adjusting Electric Trailer Brakes for Safe Towing

Electrical drive systems with the variable levels of braking power can be adjusted based on the specific road conditions, loads, and your preferences. The increase in speed while you are pulling a heavier load requires that you will need more braking force than a light one. For the bumpy, loose, and damp road conditions, the braking force needed will be less to prevent roll your wheels.

Being certain that the brakes need to warm up under a speed of 25 to 45 mph or through several stops prior adjusting the gain is required. Warm brakes are more responsive compared to cold ones that it is very important to make sure that they are warmed up adequately before undertaking any adjustments. As well, replicate life scenarios by loading trailer with normally placed load because needed gain is based on the same factor.

Tow the trailer at around 25 mph and brake normally on a dry, paved road. Gradually boost the gain (brake force) until the brakes nearly lock up, then reduce it until the trailer comes to a smooth stop without locking up. If your control has an adjustable delay setting, fine-tune it too so the tow vehicle and trailer work smoothly when you brake.

If the trailer brakes seem fine in the service bay but don’t work properly when driving, the issue might be with the vehicle controller. Some controllers have built-in diagnostic LEDs that light up to show different operating conditions and faults.

Identifying and Fixing Electric Trailer Brake Problems

For instance, how to approach vehicle controller the exact way this article suggests. Secondly, connect a voltmeter or a 12 test lights to the trailer connector of your car directly. Press in on the switch the tool has on it and confirm you get at least maximum voltage output in 3 or 4 seconds. Alternatively, without doing so, ask about voltage output of the controller next. And if the controller is putting out a correct voltage, then issue is in wiring from controller to the trailer connector. In case when you’re not seeing the expected result that could indicate the controller is defective.

If the brake light switch is not sending a signal to the controller when you depress the brakes, this could be the reason why your brake isn’t working properly. With the key on, the combination display should show some value. It means that the controller should be working. In case if there is no output, check if there is connection between the brake light switch and controller. Furthermore test if the controller is getting voltage from the battery and is grounded stable.

Controllers that work based on momentum need to be installed correctly, either level or within a specified number of degrees, to detect changes in momentum accurately. If someone has moved or reinstalled the controller, it might mess up the brake adjustment.

If the wires used to carry the current are too small for the amp load in the trailer circuit, it can cause electrical braking problems. Ensure that the wires for both the positive connection from the controller and the negative ground wires going back to the tow vehicle are at least 14 gauge or larger. Use soldered or compression (crimped) connectors, not pinch-style connectors, for wiring connections. Don’t use the trailer frame or brake cluster backing plate for ground connections. And wire the brake magnets in parallel, not in series, for the best performance.

Tips for Maintaining Your Trailer Brakes

Wheel bearings need regular maintenance, especially on boat trailers due to water exposure. Every year, it’s important to take out the bearings, clean them, check for damage, refill them with fresh grease, and adjust them properly. Some experts advise against using pressurized hub bearing caps because too much pressure can push grease past the seals, causing brake lining contamination. Make sure to set the wheel bearing preload according to the manufacturer’s specifications.

When servicing the wheel bearings, inspect the brakes too. Replace any worn, damaged, or heavily corroded parts. Adjust drum brakes so the linings lightly touch the drums. Lubricate the points where the brake shoes touch the backing plates with moly-type brake grease, as well as all hinges, adjusters, and actuator levers.

If a brake line has been opened to replace a part, bleed the brake lines to remove any air. Replacing the brake fluid annually as part of preventive maintenance can also help prevent internal corrosion, prolonging the life of the master cylinder and wheel cylinders or calipers, particularly on boat trailers.