Adjusting Drum Brakes
Brief information on various adjustment mechanisms for drum brakes:
The adjustment mechanism is designed to compensate for brake shoe wear. There are several different designs to tackle this problem.
- The S-cam has no adjustment.
- An adjuster arm is used to adjust the play and to compensate for wear to the drum brake shoes. HALDEX is a first-class supplier of adjuster arms.
- Hydraulic brakes that have an adjustment mechanism always have it built into the brakes.
- The adjustment mechanism can be manual or automatic.
- There should always be slight play between the brake drum and the brake shoes. When adjusting manually you should aim for "light contact". The total play across the diameter may be around 0.5 mm. The manufacturer will specify the amount of play and where and how you should measure it.
- Automatic adjustment mechanisms work by adjusting themselves to take up play when this becomes excessive, usually by means of a ratchet that moves on the return stroke.
- The automatic system is vulnerable to corrosion. The National Road Administration sometimes orders brakes for its road-salting vehicles with special stainless steel adjustment mechanisms, which increases the price several times.
- In the case of Simplex brakes combined with a parking brake, adjustment is by means of a pushrod, which is very vulnerable to corrosion.
- Car trailers use an adjustable lever arm mechanism with manual adjustment
The brake actuating cable should always be adjusted after adjusting the brakes themselves. Often this step is not done properly.
A wedge that is screwed in to increase the distance between the brake shoes and compensate for wear to the friction lining.
Read more about adjusting multi-disc brakes >>