Pre-Trip Inspection: Brake Components
6 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 393.47, 49 CFR 396 Appendix A
What you need to know
The chamber is where air becomes movement.
Everything after it, the pushrod, slack adjuster and S-cam, is linkage carrying that movement to the lining.
Audible air leak at brake chamber (Example-ruptured diaphragm, loose chamber clamp, etc.).
49 CFR 396 Appendix A
It is named for its job.
As the lining wears, the pushrod has to travel further; the slack adjuster shortens that travel back to where it should be.
(5) Readjustment limits. (a) The maximum pushrod stroke must not be greater than the values given in the tables below
49 CFR 396 Appendix A
Stroke is how far the pushrod travels when the brakes are applied.
It is measured with the engine off at 80 to 90 psi with the brakes fully applied.
The maximum pushrod stroke must not be greater than the values given in the tables below
49 CFR 396 Appendix A
The lining is the sacrificial surface.
Its minimum thickness differs by axle: steering axles get a larger minimum than non-steering ones.
Brake linings or pads.
49 CFR 393.47
The drum turns with the wheel, so friction against it is what slows you.
That is also why a crack opening under brake application puts it out of service.
Brake drums or rotors.
49 CFR 396 Appendix A
It sits on the camshaft with the pushrod attached to its outer end, so it is visible from outside the wheel without removing anything.
Mismatch across any power unit steering axle of:
(a) Air chamber sizes.
(b) Slack adjuster length.
49 CFR 396 Appendix A
Check yourself
- The part that converts air pressure into mechanical force is:
- The part that takes up the slack as your linings wear is:
- On which part do you measure stroke during an inspection?
- The part that wears against the drum and is checked for thickness is:
- The linings press outward against which part to slow your wheel?
- Walking your vehicle, where would you find the slack adjuster?
Answers are in the practice test for this topic.