The purpose of this article is to help mechanics like you avoid improper rear drum brake adjustments. As you read, take note of the different common mistakes and how to stay away from them. Likewise, you may notice that there are several ways to ensure a quality job.
Rear Drum Brake Adjustments
One common problem when dealing with rear drum brakes is that mechanics don’t understand when and how self-adjustment occurs. As a result, improper adjustments can occur. On the other hand, learning to identify the self-adjusting parts and when they operate will allow the following:
- Determining whether the self-adjusting mechanism is operating as designed.
- Allow proper assembly or repair of self-adjustment mechanism
- Identify when self-adjustment takes place
Duo-Servo Drum Brake
You can identify duo-servo drum brakes by the location of either the self-adjuster or anchor pin. Likewise, the location of the self-adjuster is at the bottom between the primary and secondary brake shoes. Likewise, the anchor pin is at the top between the two brake shoes.
All duo-servo drum brakes are designed to self-adjust when backing up only under the following conditions:
- There is a large enough gap between the secondary brake shoe and the brake drum.
- The parts that make up the self-adjusting mechanism are operating correctly.
When servicing vehicles with duo-servo drum brakes, it is essential to make sure all parts are lubricated and installed correctly.
Non-Servo Drum Brake
Often times FWD vehicles have non-servo drum brakes. As a result, the most distinguishing feature of a non-servo drum brake is the location of the anchor pin. For example, the anchor pin on non-servo drum brakes is at the bottom of the backing plate.
There are two techniques used to allow self-adjustment on non-servo drum brakes. The most common is during any forward braking. For the vast majority of FWD vehicles use this method. There are a small number of non-servo drum brakes that use the parking brake to self-adjust.
A good rule of thumb is to use the self-adjuster’s location to help determine when self-adjustment takes place. In the case that you notice that the self-adjuster is part of the strut rod self-adjustment occurs during forward braking. For instance, If the self-adjuster is part of the parking brake lever then self-adjustment occurs during parking brake use.
While these rules of thumb are pretty accurate, they do not apply to all cases. Another way to determine when self-adjustment takes place is to engage both methods and see which one works.
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