How to Adjust Truck Brakes

by Jody L. Campbell

Since disc brakes in a truck cannot be adjusted, it's important that rear drum brakes be adjusted regularly. The rear drum brakes on a truck provide only 25 percent braking capacity if properly adjusted. If they are not, the percentage goes down. This becomes a problem for the front brakes as they will overwork to compensate for the lack of braking capacity in the rear. Though there are many makes and models of trucks on the road, adjusting the brakes is generally universal.

How to Adjust Truck Brakes

Place the truck in neutral and lift it on a lift. Remove the rear wheels using an impact gun and a socket to remove the wheel nuts.

Inspect the back of the backing plates behind the drums for brake adjustment portholes or recessed indents of the backing plates for porthole options. Some manufacturers do not have the recessed indents punched out, and this can be done simply with a chisel and hammer. It's best to remove the drums first to inspect the correct adjustment application for the vehicle. Remove the rubber porthole adjustment plugs or punch out the recessed indented covers with the hammer and a chisel. In the event there are two indented covers--the backing plates are often manufactured to accommodate both left and rear wheels and offer access to the offset adjusting mechanisms--you can punch out both or remove the drum first to locate the adjusting mechanism.

Remove the drum. Sometimes the drums are either stuck to the rear hub from rust and corrosion. Other times they can be stuck on the brake shoes, retained by a ridge or lip on the inside diameter of the drum. In this case de-adjusting the brakes would be helpful to remove the drum but may not be a viable option without knowing the location of the adjusting mechanism. Smacking the hub of the drum with a hammer can usually break it free from the hub. If the drum is hung up on the shoes by a ridge or lip, you may have to punch out those recessed indentations to locate and de-adjust the rear shoes. Remove the drum.

Locate the star wheel adjuster mechanism--at the top or bottom--of the rear brake system. If you haven't punched out the recessed indentation cover yet, do so at this time and align the porthole with the star wheel of the adjuster.

Press the star wheel retainer clip away from the star wheel from the porthole location and use the brake adjusting tool to turn the star wheel. While doing this, take a look at the way the star wheel adjuster is moving. Moving the star wheel one way will retract the threads of the adjuster screw attached to the star wheel. This will de-adjust the rear brakes. Moving the star wheel in the opposite direction will expand the screw and move the shoes outward. This would be the way you want to move the star wheel to adjust the shoes to the inside diameter of the drum. Remember which way to move the star wheel.

Reassemble the rear drum, wheel and lug nuts. Tighten the lug nuts to the proper recommended torque specifications.

Lift the truck high enough to comfortably access the porthole through the backing plate. Press the star wheel retaining clip inward with the long thin screwdriver. You'll have to feel for it since you won't be able to see it through the small porthole. Then use the adjuster tool to move the star wheel to adjust the brake shoes outward. Turn the wheel physically every three or four clicks of the star wheel to feel for the brake shoes dragging.

Adjust and tighten the parking brake cable on that side. There are too many truck makes and models to determine which procedure to perform, but a repair manual for your truck would be helpful. Parking brakes assist in keeping the rear brakes adjusted once set properly. Using the parking brake every time you park will help the longevity of keeping the rear brakes adjusted.

Repeat the procedure for the other side. You may not have to remove the other wheel unless you need to punch out the recessed indented cover. Getting a feel for the correct drag is a bit difficult since most trucks are rear wheel drive and turning the wheel to feel for brake drag is also moving the rear drive shaft and transaxle. Don't overadjust the rear brakes so that the wheels will not turn, but adjust them so you can feel some resistance in the wheels but can still move them.

Items you will need

About the Author

Jody L. Campbell spent over 15 years as both a manager and an under-car specialist in the automotive repair industry. Prior to that, he managed two different restaurants for over 15 years. Campbell began his professional writing career in 2004 with the publication of his first book.