How to Add Surge Brakes to a Boat Trailer

A small boat trailer such as this can benefit by installing brakes.

Most large boat trailers come equipped with trailer brakes, since they are required by law. Adding brakes to smaller trailers is a good idea, allowing quicker stops and less wear on the brakes of the tow vehicle. The project will consist of installing three parts to a trailer brake system: the coupler/actuator, the brake lines and the brake mechanism. Though all the components can be purchased separately, buying a kit with all the parts you'll need will be a better value and ensure you have all the needed fittings, lines, nuts, bolts and couplers.

Things You'll Need

• Wrench set
• Socket set
• Trailer jack
• Drill
• 1/2-inch drill bit
• Flat screwdriver
• Hammer
• Flare-nut wrench
• Hacksaw
• Nylon zip ties

Instructions

Actuator/coupler

1. Unbolt the original coupler assembly from the tongue of the trailer using appropriately sized wrenches and sockets then remove.

2. Attach the surge brake actuator coupler. The bolt pattern for couplers is fairly standard, so the bolt holes on the new coupler should line up with the original holes. If not, mark the places holes need to be on the trailer tongue and drill them with a 1/2-inch bit.

3. Bolt the new actuator/coupler into position.

Brakes

1. Jack up one wheel of the trailer high enough to remove the wheel, then remove the wheel.

2. Remove the old wheel hub by prying off the dust cap, removing the cotter key which holds the spindle nut in place and then unscrewing the spindle nut. Once the spindle nut is removed, pull firmly and the hub, bearing and seals will slide off the spindle.

3. Attach the brake caliper support to the brake attachment bracket welded to almost all boat trailer axles.

4. Install the new wheel hub with the attached brake rotor by sliding it onto the spindle. Make sure the outer bearing is in place, followed by the bearing washer then replace the spindle nut and cotter key.

5. Replace the dust cap by tapping it back into position.

6. Bolt the part of the brake caliper with the brake line connection and piston into position onto the caliper support.

7. Clip the inner brake pad to the caliper-half you mounted in step 6 and then clip the outer brake pad onto the remaining half of the caliper.

8. Bolt the two caliper halves together.

9. Repeat steps 1 to 7 on the wheel on the opposite side of the trailer.

Brake Lines

1. Attach the coupler on the end of the main brake line to the fitting on the rear of the actuator using an appropriately sized flare nut wrench.

2. Route the main brake line along the frame of the trailer, attaching it using nylon zip ties as needed to hold it firmly in place. Slight bends in the brake line can be made by hand, but abrupt bends should be made using a brake line bending tool.

3. Attach a brake line to one of the brake calipers by screwing the fitting on the end of the brake line into the port on the rear of the caliper using a flare nut wrench.

4. Use a brake line bending tool to bend the brake line down from the caliper, then bend again to run the line across the axle, bending it again as needed. Then cut it to length with a hacksaw and attach a fitting to the end of the line, and fit it into the port on the other brake caliper.

5. Cut the main brake line with a hacksaw close to where it would intersect with the wheel to wheel brake line on the axle.

6. Cut the wheelto-wheel brake line with a hacksaw close to where it would intersect with the main brake line.

7. Attach a compression coupler on the end of the main brake line using a flare nut wrench.

8. Attach a compression tee-fitting to reconnect the cut ends of the wheel-to-wheel brake line.

9. Attach the short flexible rubber brake line section to the end of the main break line and to the remaining barb of the tee-fitting in the wheel to wheel brake line.

Tips & Warnings

• Add brake fluid to the reservoir in the actuator/coupler. Open the bleeder nipples on each caliper with a flare nut wrench and use a flat blade screw driver to actuate the master cylinder in the actuator, forcing the fluid into the brake lines and driving out all of the air. Once all the air has been removed, close the bleeder nipples, and add brake fluid to the reservoir up to the full mark.

• If the axle on your trailer is one of the few which are made without a brake mounting bracket, you will have to purchase a new axle for the trailer.

References

• Jamestown Distributors: Boat Trailer Brakes

Resources

• Eastwood Tools: Brake line bending tool