VISION
D R I V ERS HANDB O O K
46
Parking Brake, Units With Air Brakes
On Blue Bird Vision buses equipped with air brakes, the rear wheel air chambers
also enclose powerful coil springs. These springs automatically apply the rear brakes
whenever air pressure is absent. These spring brakes also serve as the Driver-con-
trolled parking brake.
The parking brake knob is an air valve which, when pulled outward, releases
air pressure from the rear wheel chambers. This allows the springs to apply the rear
brakes.
Pushing the parking brake knob inward allows air brake system air pressure to
retract (cage) the coil springs. If air pressure is insufficient for safe normal air brakes
operation, the air pressure is also insufficient to disengage the spring brakes. Thus,
it is not possible to release the parking brake until sufficient air pressure has built up
in the system.
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