Truck or terminal tractor air brakes won't release: low air
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Applies to: Autocar ACTT Xspotter and other air-brake trucks and yard tractors
Symptoms
- Parking brake won't release
- Air pressure slow to build or drops quickly
- Hissing at idle
Why it happens
Spring brakes stay applied until air pressure is high enough. A leak, a failing compressor or governor, or a wet or frozen air dryer keeps pressure too low.
How to fix it
- Watch build-up time on the gauge against the manual spec.
- Listen and soap-test fittings and hoses for leaks.
- Drain the air tanks and check the air dryer.
- Check governor cut-in and cut-out pressures.
Tools and parts
- Soapy water spray
- Air dryer cartridge
What the factory service manual covers
Air system: build-up specs, governor settings, dryer service. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.