Stopping Power: The Physics and Maintenance of Air Brake Adjustment

The truck 'pulling' to one side during braking or a soft, mushy brake pedal feel are classic signs of adjustment issues.

Over-heated brakes (smoking or glowing) often indicate a brake that is too tight or a dragging slack adjuster.

Internal failure of the Automatic Slack Adjuster (ASA) mechanism.

Worn S-cam bushings or rollers creating excessive play in the linkage.

Brake drum 'out-of-round' causing uneven wear and heat spotting.

Lack of lubrication on the grease fittings leading to seized components.

Measure the 'applied stroke' by having someone apply the brakes while you measure the pushrod movement.

Ensure the stroke does not exceed the legal limit (usually 2 inches for a standard Type 30 chamber).

Check that the slack adjuster and pushrod are at a 90-degree angle when brakes are applied.

Grease the S-cam and slack adjusters monthly to ensure free movement.

Never manually adjust an automatic slack adjuster that isn't working—it is broken and needs replacement.

Check your brakes before entering any mountainous terrain or long downgrades.

Look for 'blueing' on the drums, which indicates excessive heat and potential hardening of the surface.

If you have a brake chamber that is leaking air (can be heard when brakes are applied).

When you notice a cracked brake drum or a lining that has separated from the shoe.

If you fail a roadside brake inspection and need immediate adjustment or parts to continue.

Your brakes are your life. Don't take chances with adjustment or worn linings.

Modern automatic slack adjusters are great, but they still need regular visual verification.