What Are Surge Brakes On A Trailer?

Surge brakes are one of the three major types of braking systems commonly in use on trailers today. They work by capturing the forward force of a trailer on the tow vehicle generated when the tow vehicle’s brakes are applied. That captured energy is converted to hydraulic pressure which activates the trailer’s brakes.

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Surge brakes are very common on boat trailers because they don’t require any electrical input which could be damaged or destroyed while submerged. They are also popular choices on trailers that are used on multiple vehicles, or by people who are generally unfamiliar with towing or the use of electric trailer braking systems.

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Trailer frame/tongue design and the higher vehicle weights of travel trailers limit the use of surge brakes in that trailer segment. Nearly all medium to large-sized travel trailers will be equipped with some form of electric brakes from the factory. Surge brakes do have a place in the travel trailer arena and they may be the best option for your application. Let’s take a look at surge brakes to see if that’s the case.

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What’s The Maximum Weight Surge Brakes Can Handle?

Like all trailer braking systems, the brakes are matched to the axles which have a specific load-carrying capacity. As such, the maximum trailer weight is not dictated by the brakes, but rather the axles and/or frame components of the trailer. In the case of surge brakes, the actuator also plays a role in the maximum trailer weight.

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Because the actuator contains moving parts, and functions as a key structural component of the trailer tongue, it will be rated to two specific weights. This is not an issue related to braking power or overall braking performance of the system, it is instead the max weight that the actuator mechanism itself is capable of safely handling.

There are currently surge brake actuators on the market rated for towing up to 20,000 lbs. These are the exception as most units will be rated for smaller trailers tipping the scales under 10,000 lbs.

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How Do You Know Your Surge Brakes Are Working?

As with any braking system, it is important to be able to test your surge brakes to make sure they are functioning correctly. Since surge brakes do not rely on any electrical input from the tow vehicle to activate, they can be more difficult to test than an electrical brake system.

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To test the brakes, the hydraulic actuator must be activated. While this isn’t as easy as pushing a button on an electrical brake system, there are several easy ways to get it done:

  1. Try backup up the trailer. If you have a manual or electric reverse lockout, make sure that is disconnected or turned off since it will prevent the brakes from activating. When you backup, the brakes should activate making the trailer hard to move. This will work best with disc brake based surge systems. If your system is drum brake based then you may see anywhere from complete brake activation to minimal brake dragging. Many drum brake designs do not work well in reverse so failure to stop well is not necessarily an indication of a problem.
  2. Take the trailer for a drive with everything properly hooked up. Stop several times in a short distance. Use an infrared temperature gauge to measure the temp of the discs or drums on the system. If they are hot, they are working.
  3. Attach the trailer to the tow vehicle. Activate the breakaway lever and slowly attempt to move the trailer. If the brakes are working correctly the brakes will be on and it won’t move easily.
  4. To test a specific wheel, jack it off the ground and confirm it rotates freely. Manually push in the actuator, or active the breakaway level and recheck the wheel. If it still rotates freely the brakes are not working correctly.
  5. Check your master cylinder fluid level. If it is dry you must assume the brakes do not work.
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Do I Need To Adjust My Surge Brakes?

Brake adjustment on a surge brake system will depend on the specific braking hardware that your system use. Adjustments are not necessary on surge brake systems that use disc brakes, while drum brakes will require periodic adjustment.

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As disc brakes wear, they automatically adjust to the new pad thickness. Most drum brakes have auto-adjusting capabilities built-in, but the reliability of those mechanisms can vary greatly and may require special driving circumstances to activate properly.

The easiest drum brake auto-adjusting mechanism can be found in forward adjusting brakes. These have become more common over the past few years. They auto-adjust when the brakes are applied while traveling forward.

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These don’t require any special driving habits for the adjustment to take place so they do a good job staying adjusted, assuming they are in good mechanical condition. In many cases, they work so well that they tend to go through pads much faster than manual or reverse adjusting brakes. If you have forward adjusting brakes, make sure to inspect them frequently to catch any premature wear.

The most common auto-adjusting drum brakes adjust when backing up. To activate the self-adjusters, simply back up with the trailer brakes applied. The rotational force on the brake mechanism automatically turns the adjusters as needed. Again, this assumes your brakes are in good mechanical condition. Rust, dirt, or other debris in the brakes can affect their ability to self-adjust.

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Activating the reverse adjustment also requires good brake resistance while in reverse. If your brakes are too far out of adjustment, or simply don’t work well in reverse then it is unlikely they will properly auto-adjust when backing up.

Regardless of the brakes, you have on your trailer you should routinely check them for proper function and adjustment. While disc brakes self-adjust, mechanical issues like stuck pistons, broken or bound up pads, locked slide pins, etc. can all cause poor brake performance which mimics improper adjustment.

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By testing and inspecting your brakes frequently these issues can be found and addressed before they cause serious issues on the road. With drum brakes, routine inspection will allow you to identify and address adjustment issues.

If your self-adjusters are not doing the job, you can manually adjust to get things back where they should be. When adjusting manually, always adjust all the wheels together to prevent issues with uneven braking.

Can You Back Up With Surge Brakes?

Backing up with surge brakes can be a little more challenging than with an electric braking system. To back up with surge brakes you will need to activate the actuator lockout mechanism, which you can do in one of two ways.

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The first method involves actuating a manual lockout mechanism. This is usually a pin you install into the trailer tongue or a lever on the actuator which prevents the mechanism from compressing as you back up. The second method is more advanced, relying on an electrical lockout solenoid.

These electrically powered switches tie between the master cylinder of the brake system and the reverse light wiring in the tow vehicle. When you put the vehicle in reverse, the solenoid senses the reverse lights coming on and automatically locks the master cylinder. This prevents the brakes from actuating while you back up.

Do You Need A Brake Controller For Surge Brakes?

Surge brakes work by capturing the inertial energy between the braking tow vehicle and the trailer behind it. As a completely mechanical system, no external controllers are needed for proper surge brake function.

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As the tow vehicle slows, the trailer will “surge” forward. That forward motion is absorbed by the actuator in the trailer tongue which converts that motion to hydraulic oil pressure to actuate the brakes. The only electrical connection commonly found in a surge brake system is an electric lockout solenoid.

That solenoid is connected to the tow vehicle’s reverse light circuit. When the reverse lights are activated, the solenoid locks out the brakes so the trailer can be backed up.

How Can You Top Up Your Fluid In Your Surge Brakes?

The fluid in your surge brakes is topped off in much the same way as the power brakes in your car. The master cylinder will have a fluid reservoir with a cap on it. Remove the cap and fill the reservoir with the appropriate fluid to the level recommended by the manufacturer.

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If the reservoir should ever run dry, make sure you properly bleed the brake system per the manufacturer’s recommendations when you refill the reservoir prior to towing the trailer. Allowing the reservoir to run dry can allow air bubbles to enter the system which will negatively affect the system’s braking performance.

Do Surge Brakes Use A Drum Or A Disc Brakes?

Surge braking systems can be set up to use either disc or drum brakes. There are advantages and disadvantages to each type of brake mechanism such as:

  1. Disc brakes offer better stopping power than drum brakes
  2. Drum brakes are less expensive to buy and install.
  3. Drum brakes are more expensive and time consuming to maintain.
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As a general rule, disc brakes are considered superior to drum brakes for most surge brake systems. While they do cost more to buy and install, that initial cost difference will be offset over time by reduced maintenance costs.

The better braking performance offered by disc brakes adds heavily to their value as well. Either brake type is capable of getting the job done, just be aware of the differences when choosing which option is best for your situation.

Are Surge Brakes The Same As Break Away Brakes On A Trailer?

Unlike electric brake systems, the breakaway brake function is usually integrated into the surge brake actuator on a surge brake-equipped trailer. This is typically a light wire rope attached at one end to a lever on the surge actuator. The other end will have a hook or clip which can be attached to the ears on your hitch receiver.

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In the event your trailer becomes separated from the tow vehicle, the wire rope will be pulled tight and the lever on the actuator will be activated. Once activated, the brakes will remain locked until you physically push the lever back to the off position.