CDL pre-trip - 7-step air brake test

The 7-step air brake system test must be done with correct values and in the proper order.
Click on any photo to enlarge.

Chock the wheels.
Put on seat belt.
If air-gauges are not full, run bus engine until they are, then turn engine off.


1. Test for air leaks
Push yellow parking brake knob in (photo above).
Push service brake and hold steady for one minute. No more than 3 lbs pressure loss allowed.



2. Test low-air warning system
Turn ignition key to right but don't turn engine on.
Lower air pressure by pumping on brakes.
Low air light & buzzer must come on higher than 60 lbs.



3. Test spring brake activation
Continue reducing air pressure by pumping the brakes.
Parking brake knob should pop out between 20 & 45 lbs.



4. Test air compressor build rate
Unchock wheels.
Put seat belt back on.
Start engine.
At 85 lbs (photo above) begin timing, and ...
... At 100 lbs (photo above) stop timing.
The 15-lb interval should take no more than 45 seconds.



5. Test air compressor shut-off
Let engine continue to idle.
Air compressor should shut off at about 120 lbs. Gauges will stop rising.



6. Test spring brake hold
Pull out yellow spring brake knob.
Put foot on brake.
Shift to drive on gear selector.
Using throttle pedal, raise engine rpm to 1000, then release.
Bus should not move.



7. Test service brakes
Push service brake.
Shift to drive.
Push yellow parking brake knob in.
When it is safe, release service brake and move bus forward to 5 mph.
Hover hands over steering wheel as indicated in photo above.
Bring bus to a stop by applying firm pressure to service brake.
Determine if steering wheel turns left or right, or if brakes grind.


Pull out yellow parking brake knob, shift to neutral. End of air-brake system test.