Bleeding trailer drum brakes involves systematically removing air from the hydraulic brake lines to restore optimal braking performance. This process is crucial for safety and ensures responsive and reliable stopping power when towing.
Understanding the Importance of Bleeding Trailer Brakes
Trailer brakes are essential for safe towing, particularly with heavier loads. Over time, air can enter the brake lines, either through loose connections, worn seals, or during repairs. This air acts as a compressible fluid, reducing the pressure transmitted from the tow vehicle’s brake pedal to the trailer’s brake shoes. As a result, braking becomes spongy, less effective, and potentially dangerous, especially in emergency situations. Properly bleeding the brakes is vital to expel this air, ensuring the hydraulic system is filled solely with brake fluid and providing consistent and powerful braking performance.
Step-by-Step Guide to Bleeding Trailer Drum Brakes
Bleeding trailer drum brakes requires patience and a systematic approach. Here’s a detailed guide:
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Safety First: Ensure the trailer is securely chocked, preventing any movement. Wear safety glasses and gloves to protect yourself from brake fluid, which is corrosive.
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Gather Your Tools and Materials: You’ll need the following:
- Brake fluid (DOT 3 or DOT 4, depending on your trailer’s specifications)
- A brake bleeder wrench (specifically sized for the bleeder screws on your trailer brakes)
- A clear plastic hose (approximately 2 feet long)
- A container to collect the used brake fluid
- A helper (ideally, but a one-person bleeder kit can be used)
- Wheel chocks
- Jack and jack stands (if necessary to access the bleeder screws)
- Penetrating oil (if the bleeder screws are rusty or seized)
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Locate the Bleeder Screws: The bleeder screws are typically located on the back side of each brake drum, near the top. If the screws are rusty or difficult to turn, apply penetrating oil and let it sit for a few minutes before attempting to loosen them.
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Prepare the Bleeding Setup: Attach one end of the clear plastic hose to the bleeder screw. Place the other end of the hose into the container, ensuring the end is submerged in a small amount of fresh brake fluid. This prevents air from being sucked back into the system.
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Bleeding Procedure (Two-Person Method):
- Have your helper slowly press the brake pedal of the tow vehicle.
- While the pedal is depressed, open the bleeder screw on the first brake you’re bleeding (typically the one farthest from the master cylinder on the trailer). You’ll see fluid and possibly air bubbles flow through the hose into the container.
- Close the bleeder screw before your helper releases the brake pedal.
- Repeat steps 5a-5c until no more air bubbles appear in the hose.
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Bleeding Order: It’s generally recommended to bleed the brakes in the following order:
- Farthest brake from the master cylinder
- Next farthest brake
- Closest brake to the master cylinder
- For a tandem axle trailer, bleed one brake on the rear axle and then one on the front axle until all four have been bled.
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Monitor Brake Fluid Level: Continuously check the brake fluid level in the master cylinder reservoir of the tow vehicle. Never allow the reservoir to run dry, as this will introduce more air into the system and require the entire process to be repeated.
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Tighten the Bleeder Screws: Once you’ve bled all the brakes, securely tighten the bleeder screws. Be careful not to overtighten them, as this can damage the screw or the brake drum.
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Test the Brakes: After bleeding, test the brakes by slowly driving the trailer and applying the brakes. Check for a firm pedal feel and responsive braking action. If the brakes still feel spongy, repeat the bleeding process.
Alternative Bleeding Methods
One-Person Bleeding Kits
One-person bleeding kits are available that allow you to bleed brakes without assistance. These kits typically use a check valve to prevent air from being drawn back into the system when the brake pedal is released. Follow the instructions provided with the specific kit you are using.
Pressure Bleeding
Pressure bleeding involves using a pressure bleeder to force brake fluid through the system. This method is generally more efficient than manual bleeding, but requires specialized equipment. Be sure to follow the manufacturer’s instructions carefully when using a pressure bleeder.
Avoiding Common Mistakes
- Allowing the master cylinder to run dry: This is the most common mistake and will introduce air into the entire system.
- Using contaminated brake fluid: Always use fresh, clean brake fluid. Contaminated fluid can damage the brake system components.
- Overtightening the bleeder screws: This can damage the screws or the brake drums.
- Not bleeding the brakes in the correct order: Bleeding in the wrong order can result in air remaining in the system.
FAQs: Bleeding Trailer Drum Brakes
H3 FAQ 1: How often should I bleed my trailer brakes?
It’s generally recommended to bleed your trailer brakes every one to two years, or whenever you notice a spongy brake pedal feel or after any repairs to the brake system.
H3 FAQ 2: What type of brake fluid should I use?
Refer to your trailer’s owner’s manual to determine the correct type of brake fluid. DOT 3 and DOT 4 are common, but using the wrong type can damage your brake system.
H3 FAQ 3: Can I bleed my trailer brakes myself?
Yes, you can bleed your trailer brakes yourself if you have the necessary tools and knowledge. However, if you are not comfortable working on your brakes, it’s best to have them bled by a qualified mechanic.
H3 FAQ 4: What does it mean when my brake pedal feels spongy?
A spongy brake pedal feel is usually a sign that air is present in the brake lines. Bleeding the brakes will typically resolve this issue.
H3 FAQ 5: What are the symptoms of air in my trailer brake lines?
Symptoms of air in your trailer brake lines include:
- Spongy brake pedal feel
- Reduced braking power
- Increased stopping distance
H3 FAQ 6: How do I know if my trailer brakes are working properly after bleeding?
After bleeding, your brake pedal should feel firm and responsive. When you apply the brakes, the trailer should stop smoothly and evenly. Conduct a test run at low speed to ensure proper braking performance.
H3 FAQ 7: What if I can’t loosen the bleeder screws?
If the bleeder screws are seized, apply penetrating oil and let it sit for several hours or overnight. If they still won’t budge, you may need to use a bleeder screw extractor tool. In extreme cases, the entire brake cylinder may need to be replaced.
H3 FAQ 8: Can I reuse old brake fluid?
Never reuse old brake fluid. Brake fluid absorbs moisture from the air over time, which can corrode the brake system components and reduce braking performance.
H3 FAQ 9: How do I dispose of used brake fluid?
Used brake fluid is considered hazardous waste and should be disposed of properly. Contact your local waste management facility for information on how to dispose of it safely.
H3 FAQ 10: What is a brake bleeder wrench, and why do I need it?
A brake bleeder wrench is a specialized wrench designed to fit snugly around the bleeder screw. This helps prevent rounding off the screw and provides a better grip when loosening and tightening it. Using a standard wrench can easily damage the bleeder screw.
H3 FAQ 11: My trailer brakes lock up after bleeding. What could be the problem?
Brake lockup after bleeding can indicate several issues, including: over-adjustment of the brake shoes, a faulty brake controller, or a problem with the brake actuator. It is crucial to have the entire braking system inspected by a qualified technician.
H3 FAQ 12: Are electric trailer brakes bled differently than hydraulic drum brakes?
No, the bleeding process described here applies to hydraulic trailer drum brakes. Electric trailer brakes do not use hydraulic fluid and therefore do not require bleeding. They operate using electromagnets to activate the brakes.
By following these steps and understanding the nuances of bleeding trailer drum brakes, you can ensure a safer and more enjoyable towing experience. Remember that preventative maintenance and regular inspections are key to maintaining a reliable and safe braking system.