Bleeding electric over hydraulic (EOH) trailer brakes effectively requires a systematic approach, involving not only the standard bleeding process but also addressing the unique challenges presented by the electric hydraulic actuator. Ultimately, successful bleeding ensures that all air is purged from the brake lines and actuator, leading to optimal braking performance and safety by restoring proper hydraulic pressure. This is achieved through a combination of manual and sometimes electronic bleeding techniques, ensuring the actuator is primed and functioning correctly alongside standard brake bleeding practices at each wheel cylinder or caliper.
Understanding the Electric Over Hydraulic System
EOH braking systems represent a significant advancement over traditional surge brakes, offering more responsive and controlled braking for heavier trailers. These systems utilize an electric hydraulic actuator, typically mounted on the trailer tongue, to provide the necessary hydraulic pressure to the brake calipers or wheel cylinders. The actuator is triggered by a signal from the tow vehicle’s brake controller, allowing for proportional braking force that matches the towing vehicle’s deceleration.
Before diving into the bleeding process, it’s crucial to understand the fundamental components of an EOH system. These include the brake controller in the tow vehicle, the wiring harness connecting the tow vehicle and trailer, the electric hydraulic actuator (containing the pump, reservoir, and solenoid valves), the brake lines, and the wheel cylinders or calipers at each wheel. Air trapped within any of these components can drastically reduce braking efficiency.
The Bleeding Process: A Step-by-Step Guide
Successfully bleeding EOH trailer brakes involves a methodical approach. Here’s a detailed breakdown:
1. Preparation is Key
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Gather Your Supplies: You’ll need a wrench that fits your bleeder screws, a clear plastic hose, a container to collect the old brake fluid, DOT 3 or DOT 4 brake fluid (check your actuator’s specifications), safety glasses, and gloves. A helper can significantly expedite the process.
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Safety First: Ensure the trailer is securely supported with jack stands. Never work under a trailer supported only by a jack.
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Inspect the System: Before starting, visually inspect all brake lines, fittings, and the actuator for leaks or damage. Address any issues before proceeding.
2. Activating the Actuator (If Necessary)
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Consult Your Actuator’s Manual: Some actuators require a specific procedure to activate the pump for bleeding. This might involve a momentary application of power or a dedicated “bleed” function. Always refer to the manufacturer’s instructions.
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Manual Activation: If your actuator doesn’t have a specific bleed function, you can often simulate braking by manually applying a small amount of power to the actuator’s brake wire. However, use extreme caution and only apply power momentarily to avoid overheating the pump.
3. Bleeding at the Wheels
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Start at the Furthest Wheel: Begin with the wheel cylinder or caliper farthest from the actuator. This helps ensure all air is purged from the entire system.
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Connect the Bleeding Hose: Attach one end of the clear plastic hose to the bleeder screw on the wheel cylinder or caliper. Place the other end of the hose into your collection container, ensuring the end is submerged in brake fluid to prevent air from being drawn back into the system.
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Open the Bleeder Screw: Have your helper slowly depress the brake pedal in the tow vehicle (or manually activate the actuator as described above). While the pedal is depressed, open the bleeder screw. Observe the brake fluid flowing through the hose.
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Close the Bleeder Screw: Before your helper releases the brake pedal, close the bleeder screw tightly. This prevents air from being sucked back into the system.
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Repeat: Repeat steps 3-5 until clear, bubble-free brake fluid flows from the bleeder screw.
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Move to the Next Wheel: Proceed to the next wheel cylinder or caliper, working your way closer to the actuator. Repeat the bleeding process at each wheel.
4. Bleeding the Actuator (If Necessary)
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Locate the Bleeder Screw: Some actuators have a dedicated bleeder screw for purging air from the pump and reservoir. Consult your actuator’s manual for its location.
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Bleed the Actuator: Following the same procedure as bleeding at the wheels, connect the hose to the bleeder screw, open the screw while the actuator is active (either through the tow vehicle or manual activation), and observe the fluid until it runs clear and bubble-free. Close the bleeder screw before releasing the actuator.
5. Final Check and Fill
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Check Brake Fluid Level: After bleeding all wheels and the actuator (if applicable), check the brake fluid level in the actuator’s reservoir. Fill to the recommended level.
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Test the Brakes: Before hitting the road, perform a thorough brake test in a safe, controlled environment. Ensure the trailer brakes engage smoothly and proportionally with the tow vehicle’s brakes.
Troubleshooting Common Issues
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No Brake Pressure: If you’re unable to build any brake pressure after bleeding, double-check for leaks in the brake lines or at the actuator. A faulty actuator pump can also cause this issue.
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Spongy Brakes: Spongy brakes indicate the presence of air in the system. Repeat the bleeding process, paying close attention to each wheel and the actuator.
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Actuator Not Activating: If the actuator isn’t activating, check the wiring harness for loose connections or corrosion. Also, verify that the brake controller in the tow vehicle is functioning correctly.
Electric Over Hydraulic Trailer Brakes: FAQs
Here are 12 frequently asked questions to further enhance your understanding of EOH trailer brake bleeding:
H3 1. Why are EOH trailer brakes more difficult to bleed than standard hydraulic brakes?
EOH systems introduce an electric hydraulic actuator, which has its own internal components (pump, valves, reservoir) that can trap air. This means you need to bleed not only the brake lines and calipers/wheel cylinders but also the actuator itself.
H3 2. Can I use any type of brake fluid in my EOH system?
No. Always refer to the actuator manufacturer’s specifications for the correct type of brake fluid. Typically, DOT 3 or DOT 4 brake fluid is recommended, but using the wrong type can damage the seals in the actuator.
H3 3. How often should I bleed my EOH trailer brakes?
Bleed your EOH brakes annually, or whenever you notice a decrease in braking performance, such as spongy brakes or reduced stopping power. Regular maintenance is crucial for safety.
H3 4. Do I need special tools to bleed EOH trailer brakes?
While a standard wrench and bleeding hose are sufficient, a power bleeder can significantly simplify the process, especially if you’re working alone. Power bleeders apply pressure to the brake fluid reservoir, forcing fluid through the system and eliminating the need for someone to pump the brake pedal.
H3 5. What is the purpose of the bleeder screw on the actuator?
The bleeder screw on the actuator allows you to purge air specifically from the pump and reservoir within the actuator. This is a crucial step in ensuring the entire system is free of air.
H3 6. Can a faulty brake controller affect the bleeding process?
A faulty brake controller might not send the correct signal to the actuator, making it difficult to activate the pump during bleeding. Verify that your brake controller is functioning properly before starting the bleeding process.
H3 7. What if I can’t find a bleeder screw on my actuator?
Some older or less expensive actuators may not have a dedicated bleeder screw. In this case, you may need to consult the manufacturer for alternative bleeding procedures, which might involve manually activating the pump and loosening brake line connections.
H3 8. How do I know if air is trapped in the actuator?
Common signs of air in the actuator include weak braking performance, a buzzing or grinding noise from the actuator during operation, and difficulty building brake pressure.
H3 9. What are the risks of not bleeding my EOH trailer brakes properly?
Improperly bled EOH brakes can lead to reduced braking performance, increased stopping distances, brake fade, and ultimately, a higher risk of accidents.
H3 10. Can I bleed EOH trailer brakes by myself?
While it’s easier with a helper, you can bleed EOH brakes by yourself using a one-person bleeding kit or a power bleeder. These tools allow you to maintain pressure in the brake lines while opening and closing the bleeder screws.
H3 11. Why is it important to start bleeding at the wheel furthest from the actuator?
Starting at the furthest wheel ensures that air is pushed through the entire length of the brake lines, preventing it from being trapped closer to the actuator.
H3 12. What should I do if I still have problems after bleeding the brakes multiple times?
If you’ve bled the brakes multiple times and are still experiencing issues, it’s time to consult a qualified mechanic specializing in trailer brakes. They can diagnose potential problems such as a faulty actuator, damaged brake lines, or internal leaks.
By following these steps and addressing potential issues proactively, you can effectively bleed your electric over hydraulic trailer brakes and ensure safe and reliable braking performance. Remember that regular maintenance and careful attention to detail are key to maintaining a safe and functional braking system.