Trailer Maintenance — Trailer Safety Week

Some braking systems are not automatically adjusted. These brakes require manual adjustment. Most brake assemblies are fitted with an adjustor, which can manually adjust the brakes during hard stops. This provides the correct pressure when activating your brakes. To check proper adjustment, manually engage your brakes and have someone check to see if the hub moves or spins. If you can spin the hub by hand while the brakes are engaged, you will need to manually adjust your brake shoes. If you repair or replace brake shoes or components, your brakes need to be adjusted.

The following steps apply to most manually adjustable brakes. You should refer to the manufacturer’s axle and brake manual for proper adjustment of your system. If you do not have this manual, contact your dealer for assistance.

A general manual brake adjustment process is listed below.

• Jack up the trailer and secure it on adequate capacity jack stands.

• Be sure the wheel and brake drum rotate freely.

• Remove the adjusting-hole cover from the adjusting slot on the bottom of the brake backing plate.

• With a screwdriver or standard adjusting tool, rotate the starwheel of the adjuster assembly to expand the brake shoes. Adjust the brake shoes out until the pressure of the linings against the drum makes the wheel very difficult to turn. Note: Your trailer maybe equipped with drop spindle axles. See axle manual for your axle type. You will need a modified adjusting tool for adjusting the brakes in these axles.

• Rotate the starwheel in the opposite direction until the wheel turns freely with a slight constant drag.

• Replace the adjusting-hole cover.

• Repeat the above procedure on all brakes.

• Lower the trailer to the ground.

For more information regarding the adjustment of electric trailer brakes, click here. 

Electric Brakes

Electric brakes are actuated by an electromagnet, which grabs the armature surface of the hub when a small current is applied. The current is received by either the tow vehicle or a breakaway battery. When the trailer brakes are operated by the tow vehicle, it is important they are “synchronized” so braking is properly distributed to both the tow vehicle and the trailer. Synchronization is accomplished by adjusting the gain on the tow vehicle controller. With the tow vehicle hooked up to the trailer, make several hard stops on dry pavement. If the trailer’s brakes skid or are too sensitive, decrease the gain on the brake controller. If they do not skid, slightly increase the gain setting. Remember, this gain setting is load sensitive. Readjust the gain if the trailer’s load changes.

• Inspect for any loose or worn parts including stretched or deformed springs in the brake assembly. Replace if needed.

• Inspect the electromagnets for uneven or abnormal wear. Use a small straight edge to check for even wear. If worn, or the magnet coil has become visible, replace the magnet.

• Note: It is recommended the hub armature surface be turned when magnets are replaced. Magnets should be replaced in pairs. If you change a magnet on one hub, the opposite magnet should also be replaced.

Breakaway Brake Battery

This battery supplies a current to operate the trailer brakes, if the trailer breaks away from the tow vehicle. Check the battery for proper power level.

Breakaway Switch

This switch activates the breakaway battery to supply a current to the electric breaks if the trailer breaks away from the tow vehicle. A cable for the pull pin is connected to the tow vehicle and the switch is located on the trailer.

In order to test the breakaway system, the trailer should be hitched to the tow vehicle. 

• Unplug the trailer connector from the tow vehicle

• Pull the pin out of the breakaway switch. This will take 40 pounds of pull.

• Try to tow the trailer.

• All of the wheels should be locked up and will brake so the trailer is unable to roll freely.

• Re-insert pin to the breakaway switch and reconnect the trailer plug to the tow vehicle.

• Charge the breakaway brake battery as necessary.

 Testing Breakaway Systems. (2011, August 11). Retrieved March 20, 2018, from https://www.etrailer.com/faq-tb-11-06-test-trailer-breakaway-system.aspx

Hydraulic/Surge Brakes

Hydraulic or surge brakes are among the most common braking system used on trailers in the rental industry. Unlike electric brakes, they do not require any special device or controller in the tow vehicle.  

Surge brakes are activated by the stopping inertia created between the tow vehicle and the trailer. When the tow vehicle reduces speed, pressure is applied to an actuating coupler on the trailer. The pressure forces hydraulic fluid from a master cylinder in the actuator coupler, through hydraulic lines, to a wheel cylinder which, in turn, applies force against the brake shoes and hub.

Because surge breaks are a self-contained systems, upkeep is vital to safe and reliable operation. The key to a successful and lasting operation of the surge brake unit is to keep the master cylinder free of contamination, and always maintain proper levels of brake fluid.