2-34
Parking Brake, Units With Air Brakes
On Blue Bird VISION buses equipped with air brakes, the rear wheel air chambers also enclose pow-
erful coil springs. These springs automatically apply the rear brakes whenever air pressure is absent.
These spring brakes also serve as the Driver-controlled 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. See Section 5 for more details.
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