Rear Brake Drum Adjustment

Smart and simple rear brake drum adjustment
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Article updated October 2011

Drum brake adjustment proves that wise adage about an ounce of prevention. A simple rear brake adjustment can prevent more expensive repairs down the line. Also, they don't call the parking brake an emergency brake for nothing. A complete drum brake adjustment includes making sure the emergency brake will hold within the intended range of actuator (foot pedal or hand lever) movement, preventing a minor annoyance from becoming a major emergency.

Even though four-wheel disc-brake systems are the preferable way to go—or rather, stop—many vehicles still come equipped with front disc/rear drum systems. And while rear brakes only handle about 25 percent of the braking load, they're still a very important piece of the proverbial braking "pie." If they're not working at peak efficiency, the load they're not carrying, and subsequent wear-related problems, gets foisted on the front brakes. Also, if the vehicle's braking system is a bit under-designed to begin with, the results can be dramatic. Brake rotor "hot-spotting" or even surface cracks, brake pad wear or surface "glazing" can develop—part of a vicious cycle that translates to the driver as a vehicle becomes more and more difficult to stop.

Adjustments

If the two main adjustments that affect rear brake shoe operation are not set correctly, the above scenario can and probably will occur. These adjustments are rear brake shoe adjustment and parking brake adjustment. Rear brake shoe adjustment is for the purpose of putting the brake shoes in the proper relationship to the brake drums, and is accomplished by (usually) some sort of "self-adjusting" mechanism, which will need to be manually set up at the time the shoes are replaced. It's also recommended that its operation is inspected at routine vehicle maintenance intervals and manual adjustment/service be performed at that time, too.

Emergency brake adjustment is for the purpose of making the vehicle's parking brake feature operate within the intended range of actuator (foot pedal or hand lever) movement. Its adjustment should be checked at brake shoe replacement and routine vehicle maintenance intervals as well. While we are not going to discuss performing an entire rear brake shoe replacement procedure here, we should highlight some important points for inspection and adjustment of these two parameters, as well as some common mistakes and omissions which can occur during servicing.

We'll assume that you are planning to not only replace the brake shoes, but also the wheel cylinders, and at least the brake spring hardware kit. Before you undertake those tasks, inspections should be made of the following components, and certain questions should be asked concerning them:

Parking Brake

Does the parking brake system work properly-that is, does it hold the car securely on an incline? If not, is the actuator itself working within its intended operating range, and does the ratchet mechanism hold? If the ratchet mechanism doesn't hold the actuator in place, it must be repaired or replaced. If the actuator is working within its operating range, and is being held in place by the ratchet, check to make sure that both wheels are being braked. If that's the case, but braking force is weak, the shoe replacement procedure and the adjustment procedures that we are about to describe should improve that.

Cable System

If only one wheel is receiving braking, inspect the complete braking cable system for signs of a damaged or binding cable or a malfunctioning "equalizer" (check your manual for specifics). If all is working smoothly, the shoe replacement procedure/adjustments should correct this, as the brake shoe adjustment on the suspect wheel is likely the culprit.

Pedal Height

Check brake pedal height by pushing down on the pedal. If the brake pedal seems a bit "low" (although firm), try applying the parking brake then rechecking the height. If it is now higher, over-tightening of the parking brake is suspected, which will be corrected by our outlined adjustment procedure.

Return Springs

All return springs involving parking brake or brake shoes should be inspected for damage, and replaced as needed. After you have done this brake servicing procedure and just before you put the drums on and bleed the hydraulic system, you first want to determine if the parking brake adjustment is set correctly. Depending on design, the brake shoes, when viewed from the top, should be making firm contact with either the anchor pin, or the wheel cylinder contacts (absence of an anchor pin would indicate this design). If not, you'll have to loosen the parking brake adjuster until contact is made for both left and right wheels. Poor return springs, or a binding/malfunctioning cable/equalizer could prevent success here.

More Adjustments

Now, with that done, we can adjust the brake shoe adjusters (yes, that sounds a bit redundant, but stay with us here). It should be said that certain imported vehicles have excellent self-adjusting mechanisms, which move the brake shoes into perfect adjustment with nothing more than a couple of firm applications of the brake pedal. We will discuss the other widely used system involving the star-type adjuster. These should always be cleaned and lubricated as part of the brake shoe replacement procedure. Since there is a left- and right-side adjuster, make sure that they are installed on their respective sides. Some actually have an L or R stamped on them, but if not, look at the relationship between the ratchet teeth (star) and the adjuster pawl (moved by the adjuster cable). Most pawls move upward, during self-adjusting operation (important to verify this), so the "flat" portion of the ratchet teeth should aim down. Got it? If not, please get professional help to properly finish the job.

Now, you're ready to adjust. By all means, use the slot in the backing plate or in the drum itself to insert your adjusting tool through, so you can make the adjustment with the drum on. If no slot, you'll have to keep removing and installing the drum during the adjustment procedure, until you get it right. Keep increasing adjustment until there is a slight drag on the drum. Tugging on the parking brake cable during this procedure will "center" the shoes, so you can get a more accurate adjustment.

Finally, you're ready to bleed the hydraulic system.

Now it's time to check the rear drum brake adjustment. With the drums on, apply and release the emergency brake and brake pedal to see if they are within the operating parameters described. After doing so, double check your drum brake adjustments (yes, go through it again) and make necessary corrections. Unless the adjustments for the previous set of brake shoes were perfect, you should notice a difference in more positive emergency brake operation, and a higher, firmer brake pedal. That means your drum brakes - and emergency brake - are now going to operate at full efficiency for that extra ounce of prevention.

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