How to Install Air Brakes

Air brakes can be found on most types of semi-trucks. Air brakes are brake shoes that compress to the inside of a brake drum to stop the rear wheels from turning. Over time, excessive use of air brakes can cause the brake shoes to wear down. Once the brake shoe thickness wears to 1/8 inch, replace the brake shoes as soon as possible to prevent damage to the brake drums.

Instructions

1

Park your truck on a flat surface and turn off the engine. Pull the air brake knob out to set the air brakes. Position wheel chocks behind and in front of the front wheels. Release the air brakes by pushing in on the air brake knob.

2

Position the hydraulic jack under the center of the rear axle. Jack up the rear axle and place the jack stands under the rear axle about 12 inches away from each rear wheel hub plate. Lower the rear axle onto the top of both jack stands and leave the jack in place.

3

Loosen and remove the lug nuts from one of the rear wheels with an air impact wrench and a socket. Pull off the wheels and place them near the work area. Move to the other side of the rear axle, and loosen and remove the lug nuts with the impact wrench and socket. Pull the wheels off and place them near the work area.

4

Slide under the rear axle and locate the slack adjuster that is mounted to the rear axle. The slack adjuster has an adjustment bolt that tightens and retracts the brake shoes away from the brake drum. Turn the adjustment bolt on the back of the slack adjusters counterclockwise to retract the brake shoes away from the surface of the brake drums. This will make it easier to remove and install the new air brake shoes. Repeat this process for both slack adjusters on the rear axle.

5

Pull the brake drum off the driver's side rear wheel hub first and place it on the ground. Remove the brake shoes by removing the top and bottom brake shoe springs with the brake shoe spring removal tool. Place the springs on the ground near the work area. Pull on the top of the brake shoes until they are separated. Place the old air brake shoes on the ground near the work area.

6

Position the new brake shoes onto the brake shoe backing plate. Position the brake shoes so that the top of the brake shoes are positioned against the anchor pin and the bottom of the brake shoes are positioned against the brake shoe adjuster. Reattach the brake shoe springs to the top and bottom of the brake shoes with the brake spring tool.

7

Push the brake drum completely over the brake shoes. Slide the wheels back onto the brake drum and screw the lug nuts on tightly. Finish tightening the lug nuts with the air impact wrench and socket. Move to the other side of the rear axle and repeat the same process to remove the old brake shoes and to install the new ones.

8

Jack back up the rear axle with the jack and remove the jack stands. Lower the rear axle to the ground. Pull the jack out from under the rear axle and place it under the front-rear axle. Repeat the same process to remove the old brake shoes and install the new ones on the front-rear axle.

9

Jack up the front-rear axle and remove the jack stands. Lower the front-rear axle and remove the jack. Slide under the truck and adjust each brake shoe to the proper distance from the brake drum. Turn each slack adjuster adjustment bolt clockwise with a ratchet and a socket until the brake shoes are compressed to the surface of the brake drums. Once the brake shoes are compressed, the adjustment bolt will stop turning. Turn the adjustment bolts counterclockwise between 1/4- to 1/2-turn to set the brake shoes to the proper distance away from the surface of the brake drums.

10

Crank the engine back up and allow the air pressure to build up to at least 120 psi. Pull the air brake knob out for about five seconds and then push it back in to finish setting the brake shoes to the brake drums. Remove the wheel chocks. Drive the truck around to test the new air brakes.