How to Look After Your Trailer’s Hydraulic Disc Brakes

How to Look After Your Trailer’s Hydraulic Disc Brakes

Your trailer’s brakes are one of the most important bits of kit when you’re towing. If they’re not working properly, you’re putting yourself, and everyone else on the road at risk. Hydraulic disc brakes need regular maintenance to stay opperating smoothly, and that means draining, cleaning, topping up and bleeding the system from time to time.

At TWL we stock the brake fluid, pads, tools and safety gear you’ll need, so you can sort the job properly and tow with confidence.

Why Brake Fluid Maintenance Matters

Brake fluid isn’t something you can just forget about. It’s hygroscopic, which means it absorbs moisture from the air. Over time, that moisture builds up until you have more water than brake fluid.

As well as causing internal corrosion and pitting of brake components, water can cause major problems under heavy braking.

Good clean brake fluid has an extremely high boiling point and under normal braking conditions can dissipate the heat generated without issue, but when the absorbed water in contaminated brake fluid heats up, the water turns to steam and when compressed under load, can saturate the fluid with air bubbles causing loss of braking power and potentially a serious accident.

Step 1: Gear Up

Before you start, make sure you’ve got what you need:

Step 2: Prep the Trailer

Park on level ground, chock the wheels, and engage the trailer parking brake. Jack the trailer if needed, and use axle stands for safety. Remove the wheels.

Step 3: Find the Reservoir

The hydraulic brake reservoir is usually near the hitch or on the drawbar. Pop the cap to access the fluid.

Step 4: Drain the Old Fluid

  1. Clean the area around the brake reservoir to prevent dirt and debris from entering.

  2. Attach the clear plastic hose to the brake bleeder valve on one of the brake calipers. Place the other end of the hose into the catch container or jar.

  3. Using the spanner, loosen the bleeder valve by turning it counterclockwise about half a turn. This will allow the old brake fluid to flow out through the hose. There is the high possibility that the bleed screw is corroded and tight, if so, spray some CRC or similar on the bleed screw and leave for a few minutes before trying again. Be careful not to use too much force to undo the bleed screw, they are prone to snap or round off.

  4. Gently pump the brake lever on your trailer or in the case of Electric or Air over Hydraulic systems (EOH or AOH), get someone to turn the tow vehicle ignition on and pump the tow vehicle brakes to activate. This will push the old fluid out through the hose. Make sure that the brake reservoir does not empty out and continuously top the fluid up during this time.

  5. Continue pumping the brake lever or pedal until the fluid runs clear, ensuring all old fluid and air bubbles are purged from the system. Again, monitor the fluid level in the reservoir to avoid running it dry.

  6. Gently tighten the bleed screw and repeat the process with the other caliper until all fluid into the catch container of jar runs clear.

  7. Again, gently tighten the bleed screw up and clean up any drips and spills. Discard the contaminated fluid appropriately.

Step 5: Clean the Brake Gear

Spray brake cleaner over calipers, rotors and pads. Wipe away grime with a rag. Check pad wear – if they’re thin, now’s the time to replace them. TWL carries a full range of replacement pads and brake parts.

Step 6: Top Up

Refill the reservoir with fresh fluid, keeping it below the max line.

Step 7: Bleed the Brakes

Starting with the caliper furthest from the reservoir:

  1. Attach hose to the brake bleeder valve and jar.

  2. Get your mate or use a brake bleeding kit with a one-way valve to prevent air from being drawn back into the system.

  3. Open the bleeder valve slightly, and have your mate slowly depress the brake pedal or activate the brake lever.

    1. As your mate holds the pedal or lever down, tighten the bleeder valve.

    2. Instruct your mate to release the pedal or lever, allowing it to return to its original position. Repeat this process until no air bubbles are visible in the clear hose.

    3. Move to the next caliper and repeat the bleeding process, working your way from the farthest to the nearest caliper.

    Step 8: Final Checks

    1. Once all calipers are bled, ensure the brake fluid level is correct in the reservoir.

    2. Check for any leaks around the bleeder valves or the brake system components.

    3. Reinstall the reservoir cap securely.

    4. Test the brakes by applying gentle pressure to the brake pedal or lever. Ensure they engage smoothly and provide adequate stopping power.

    5. Take a short test drive to check the proper operation of the trailer's hydraulic disc brakes.

    Wrap-Up

    Regular brake maintenance isn’t optional – it’s the difference between a safe stop and a dangerous situation. Fresh fluid, clean components, and properly bled brakes keep your trailer ready for the road.

    TWL has the brake fluid, Brake cleaner, pads, couplings and hardware you need to do the job right. Pop into your local branch before your next towing trip and we’ll set you up with the right gear.