Service brakes on a trailer are the primary braking system used to slow or stop the trailer during normal driving conditions. They work in conjunction with the tow vehicle’s brakes to provide controlled and safe deceleration, preventing jackknifing and ensuring overall stability while towing.
Understanding Trailer Braking Systems
Trailers, especially those carrying significant loads, require their own braking systems to ensure safe operation. Relying solely on the tow vehicle’s brakes can quickly lead to overheating, premature wear, and ultimately, brake failure. Understanding the different types of trailer brakes and their function is crucial for any trailer owner or operator.
The Role of Service Brakes
Service brakes are the workhorses of trailer braking. Unlike emergency or parking brakes, they are actively used during every stop and slowdown. Their primary purpose is to provide controlled deceleration in response to the driver’s input via the tow vehicle’s brake pedal. The performance of service brakes directly impacts the safety and stability of the entire towing rig.
Types of Trailer Service Brakes
Several types of service brakes are commonly found on trailers, each with its own advantages and disadvantages. The choice depends on factors like trailer weight, application, and cost.
Electric Brakes
Electric brakes are the most common type found on smaller to medium-sized trailers. They operate using electromagnets that are energized when the tow vehicle’s brake pedal is applied. The electromagnet attracts an armature, which in turn applies force to the brake shoes, pressing them against the brake drum. The amount of braking force is proportional to the electrical current supplied. Electric brakes are relatively simple to install and maintain, making them a popular choice.
Electric-Over-Hydraulic (EOH) Brakes
Electric-over-hydraulic (EOH) brakes combine the responsiveness of hydraulic brakes with the ease of electrical control. An electric actuator, mounted on the trailer, converts the electrical signal from the tow vehicle into hydraulic pressure. This pressure is then used to actuate hydraulic brakes at each wheel, providing more powerful and consistent braking compared to electric brakes alone. EOH systems are typically used on heavier trailers and offer superior stopping performance.
Hydraulic Brakes
Hydraulic brakes, similar to those found on cars and trucks, use hydraulic pressure to actuate the brake calipers or wheel cylinders. They are often used on boat trailers and trailers that may be frequently submerged in water, as they are less susceptible to corrosion than electric brakes. Surge brakes are a common type of hydraulic brake used on trailers.
Air Brakes
Air brakes are the standard for large commercial trailers. They use compressed air to apply the brakes. Air pressure is supplied from the tow vehicle and controlled by a relay valve on the trailer. Air brakes are known for their power and reliability but require a more complex system and specialized knowledge to maintain. These are often used in commercial trucking applications.
How Service Brakes Work: A Closer Look
The specific operation of service brakes varies depending on the type of brake system used. However, the fundamental principle remains the same: converting energy into heat to slow or stop the trailer.
Electric Brake Operation in Detail
- The tow vehicle’s brake pedal is depressed, activating the brake controller.
- The brake controller sends an electrical signal to the electromagnets in the trailer’s brake assemblies.
- The electromagnets become energized, attracting the armature.
- The armature presses against the brake shoes, forcing them against the brake drums.
- Friction between the brake shoes and drums creates heat, slowing the wheel’s rotation.
Electric-Over-Hydraulic Brake Operation in Detail
- The tow vehicle’s brake pedal is depressed, activating the brake controller.
- The brake controller sends an electrical signal to the electric actuator on the trailer.
- The electric actuator converts the electrical signal into hydraulic pressure.
- The hydraulic pressure is transmitted through brake lines to the wheel cylinders or calipers at each wheel.
- The wheel cylinders or calipers apply pressure to the brake shoes or pads, forcing them against the brake drums or rotors.
- Friction between the brake shoes/pads and drums/rotors creates heat, slowing the wheel’s rotation.
Maintenance and Troubleshooting of Service Brakes
Regular maintenance is essential to ensure the safe and reliable operation of trailer service brakes. Neglecting maintenance can lead to brake failure and dangerous situations.
Common Maintenance Tasks
- Inspect brake components: Regularly check brake shoes, drums, pads, rotors, and brake lines for wear, damage, or leaks.
- Adjust brake shoes: Adjust brake shoes as needed to maintain proper clearance and ensure optimal braking performance.
- Lubricate moving parts: Lubricate brake cables, linkages, and other moving parts to prevent corrosion and ensure smooth operation.
- Check brake fluid (for hydraulic systems): Inspect the brake fluid level and condition, and replace it as recommended by the manufacturer.
- Test brake function: Before each trip, test the trailer brakes to ensure they are functioning properly.
Troubleshooting Common Problems
- Weak or uneven braking: This could be caused by worn brake shoes, improperly adjusted brakes, contaminated brake linings, or a faulty brake controller.
- Brake lockup: This can be caused by a malfunctioning brake controller, seized brake components, or improper brake adjustment.
- Brake noise: Unusual noises, such as squealing or grinding, can indicate worn brake pads, damaged rotors, or other brake problems.
- Loss of braking power: This could be caused by a leak in the brake lines, a faulty master cylinder, or contaminated brake fluid (for hydraulic systems).
Frequently Asked Questions (FAQs)
FAQ 1: How do I know what type of service brakes my trailer has?
Look at the brake assemblies on your trailer. Electric brakes will have wires running to them, typically enclosed in a conduit. Hydraulic brakes will have brake lines running to them. Air brakes will have air lines and potentially an air tank. Consult your trailer’s owner’s manual for specific information.
FAQ 2: What is a brake controller, and why is it necessary?
A brake controller is an electronic device installed in the tow vehicle that controls the amount of power sent to the trailer’s electric brakes. It synchronizes the trailer’s braking with the tow vehicle’s, preventing trailer sway and ensuring controlled stopping. It’s crucial for safe towing with electric brakes.
FAQ 3: How often should I inspect my trailer’s service brakes?
Inspect your trailer’s service brakes before each trip, especially before long journeys. A more thorough inspection should be performed at least annually, or more frequently if you tow regularly or in harsh conditions.
FAQ 4: Can I upgrade my trailer’s service brakes?
Yes, you can upgrade your trailer’s service brakes. Common upgrades include switching from electric brakes to EOH brakes for improved stopping power, or upgrading to larger brake drums or rotors for increased heat dissipation. Always consult with a qualified mechanic before making any brake modifications.
FAQ 5: What does “brake fade” mean?
Brake fade refers to the reduction in braking power that occurs when brakes overheat. As the brake components get hotter, they become less effective at creating friction, leading to longer stopping distances.
FAQ 6: How do I adjust electric trailer brakes?
Adjust electric trailer brakes by turning the star wheel adjuster inside the brake assembly until the brake shoes make light contact with the drum. Then, back off the adjuster until the wheel turns freely with a slight drag. Refer to your owner’s manual for specific instructions.
FAQ 7: What is the difference between surge brakes and independent hydraulic brakes?
Surge brakes are activated by the inertia of the trailer pushing against the tow vehicle during deceleration. Independent hydraulic brakes are activated by the tow vehicle’s brake pedal, similar to how EOH brakes work, but using hydraulic lines instead of an electric signal.
FAQ 8: Are trailer brakes required by law?
Yes, most jurisdictions require trailers exceeding a certain weight limit to have their own braking systems. The specific weight threshold varies by location. Check your local laws and regulations.
FAQ 9: What is the purpose of breakaway brakes?
Breakaway brakes are an emergency braking system that automatically applies the trailer brakes if the trailer becomes detached from the tow vehicle. They are activated by a breakaway cable that is connected to the tow vehicle. If the trailer separates, the cable pulls a pin, activating the brakes.
FAQ 10: What is the lifespan of trailer brake shoes and pads?
The lifespan of trailer brake shoes and pads depends on several factors, including towing frequency, load weight, and driving conditions. However, typically they should be inspected for wear every 12 months and replaced when they reach their wear limit.
FAQ 11: Can I use automotive brake parts on my trailer?
In some cases, automotive brake parts may be compatible with trailers. However, it is crucial to verify that the parts are rated for the trailer’s weight and braking requirements. Using incompatible parts can compromise safety. Always consult with a qualified mechanic before using automotive parts on a trailer.
FAQ 12: What is involved in converting from drum brakes to disc brakes on a trailer?
Converting from drum brakes to disc brakes requires replacing the entire brake assembly, including the backing plates, hubs, calipers, rotors, and brake lines. It may also require upgrading the brake controller or hydraulic actuator. This is a significant upgrade that should be performed by a qualified mechanic.