Slack Adjuster Operation

Slack Adjuster Operation in the air brake system is to regulate the distance between the brake drum and brake linings to apply braking and since this distance increases during the time, due to wear of brake linings, the correct function of the brake adjuster is of a great importance.

Brake adjuster, being connected to the brake chamber via clevis regulates the distance between the brake linings and the brake drum. When the brake pedal is applied, the compressed air moves through lines to the brake chamber. The air pressure inside the brake chamber moves up the diaphragm causing the piston (pushrod) to move which in turn pushes the slack adjuster. The slack adjuster turns the camshaft. The camshaft turns the s-cam, which in turn pushes the brake shoes apart to the brake drum. The friction created because of the contact of brake shoes and brake drum, slows down the wheels and stops the vehicle.(air brake system)

سیستم ترمز
figure 1

Types of brake adjusters

Brake adjusters are available in two types of manual and automatic. The difference is that when manual, the adjustments of distance between the brake drum and the brake lining is done manually using a wrench while in automatic type there is no need for manual adjustment.

Replacement and identifying a slack adjuster that fits

To identify a brake adjuster which fits correctly, three major points need to be considered as follows.

Slack Adjuster Operation
figure 2


The spline teeth of a brake adjuster fit into the spline teeth of the camshaft. Therefore, they both need to have the same quantity of teeth. An easy way to determine the number of teeth is simply by counting them. (figure 2)


The arm span of a brake adjuster is the distance between the center of the camshaft and the center of the pin hole that is used with the clevis. Many slack adjusters feature multiple pin holes so that they can be used at any of the lengths available. (figure 2)


The camshaft diameter needs to fit the inside of the socket of the brake adjuster for their teeth to fit correctly as shown in figure 2.

Leave a Reply

Your email address will not be published. Required fields are marked *