How to Add Brakes to a Boat Trailer

Written by mike schoonveld
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How to Add Brakes to a Boat Trailer
Adding a set of brakes to this trailer may be needed to make it street-legal. (trailer's suspension image by Diana Mastepanova from

Most states require trailers hauling boats or loads over a set minimum size be equipped with brakes. Both electrically operated brakes and surge brakes are available in both disc brake and drum brake configurations. Since the brakes on a boat trailer will be repeatedly submerged in water when launching and loading the boat, experts suggest surge-style brakes to eliminate submerging electrical parts, and disc brakes because they will drain more easily and dry quicker.

Skill level:

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Things you need

  • Brake actuator trailer hitch
  • Brake lines
  • Rubber-clad, flexible brake line
  • 5 brake line end fittings
  • 1 brake line tee-fitting
  • 1 pair of wheel hubs with brake rotor
  • 1 pair of brake calipers with brake pads
  • ½-inch drive socket wrench
  • Socket set
  • Box end wrench set
  • Jack
  • Jack stands
  • Flare nut wrench
  • 12V test light
  • Brake line cutting tool
  • Brake line bending tool
  • Flexible tape measure
  • Nylon zip ties

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  1. 1

    Remove the bolts holding the factory-installed trailer hitch using the appropriately-sized sockets and wrenches.

  2. 2

    Lift old hitch off the trailer tongue, brush away any rust or dirt, and set the new hitch containing the brake actuator in place.

  3. 3

    Tighten the bolts to securely fasten the hitch/actuator to the trailer tongue.

  1. 1

    Jack up each wheel on the trailer and insert a pair of jack stands under the axle, suspending the trailer wheels off the floor.

  2. 2

    Remove both wheels from the trailer.

  3. 3

    Remove the factory-installed wheel hubs by removing each hub's dust cap and castle nuts on the end of each spindle. Then pulling firmly on each hub.

  4. 4

    Assemble the replacement hubs (if necessary) by inserting the rear bearing race, rear bearing, and rear grease seal on the inner side of each hub. Insert the outer bearing race in the outside end of the hub.

  5. 5

    Slide each new hub/brake rotor assembly onto the axle spindles, insert the outer wheel bearing, washer and secure it in place with the castle nut. Tap the dust caps back in place.

  1. 1

    Attach the brake caliper support brackets to the brake mount brackets, located on the trailer axle just between the wheel hub and trailer's suspension.

  2. 2

    Install the brake pads in each of the calipers.

  3. 3

    Lower a brake caliper over each rotor so one brake pad is positioned on each side of the rotor. Attach the caliper to the caliper support bracket with the bolts provided.

  1. 1

    Measure the route you plan to run the brake lines from the actuator to the trailer axle using a flexible tape.

  2. 2

    Cut the brake line to length using a brake line cutting tool.

  3. 3

    Install a brake line end fitting onto the line, and use a brake line flaring tool to swell the end and secure the fitting.

  4. 4

    Use a brake line bending tool to make the needed bends in the brake line to make a secure installation.

  5. 5

    Attach the brake line to the frame of the trailer using nylon zip ties.

  6. 6

    Measure the route along the trailer axle to each brake assembly using a flexible tape measure.

  7. 7

    Cut the brake line to length using a brake line cutting tool, then cut the brake line near the centre, close to where it will tee into the line from the actuator.

  8. 8

    Attach a brake line end fitting on each of the ends of these two lines.

  9. 9

    Use a brake line bending tool to make the needed bends in the brake line to make a neat and secure installation along the axle and into the back of the caliper.

  10. 10

    Reattach the two axle brake lines using a brake line tee fitting, then use nylon zip ties to attach the brake line to the trailer axle.

  11. 11

    Use a short length flexible, rubber-clad brake line to connect the line from the actuator to the tee-fitting on the brake line secured to the trailer.

Tips and warnings

  • Trailer brake kits are available which include the actuator hitch, wheel hubs with rotors, new wheel bearings and seals, caliper supports, calipers, brake pads, flexible brake line and installation instructions. Some include the metal brake lines and fittings. Buying the kit is usually less expensive than purchasing each component ala carte.
  • Once the new brakes are installed, fill the brake fluid reservoir, bleed the brakes and test them before taking the trailer out on the highway.

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