Drum Brakes - Rear Brake Drum Adjustment

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.


Parking 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.