CDL Air Brakes TestAir Brake System PartsMedium
A driver notices that the air pressure gauge for the primary air tank is showing 60 psi, while the secondary tank gauge shows 100 psi. What is the most likely cause of this discrepancy in a dual air brake system?
- AThe anti-lock braking system (ABS) is active.
- BThe parking brake is partially engaged.
- CA leak in the primary air tank or its associated lines.
- DA malfunctioning air compressor governor.
Show answer & explanationAnswer & explanation
Correct answer: C. A leak in the primary air tank or its associated lines.
In a dual air brake system, separate air tanks and lines supply air to the front and rear brakes. A significant difference in pressure between the primary and secondary tanks usually indicates a leak or issue in the lower-pressure circuit.
Why the other options are wrong
- A. ABS activation is a function of the braking system, not a cause of pressure discrepancies between the primary and secondary air supply circuits.
- B. The parking brake being partially engaged does not directly cause a pressure differential between the primary and secondary service brake circuits.
- D. A malfunctioning governor would typically affect both tanks, either preventing them from building pressure or causing them to over-pressurize.
Dual Air Brake System Discrepancy
A significant difference in pressure readings between the primary and secondary air tanks in a dual air brake system typically indicates a problem in the lower-pressure circuit.
- Dual systems have separate circuits for front and rear brakes.
- Pressure differences pinpoint issues to a specific circuit.
- Leaks are a common cause of pressure drops.
Memory trick: Dual tanks, separate paths, different pressures, one big problem.