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Causes of air leakage from the handbrake valve and abnormal brake noise
1. Handbrake Valve Air Leakage
When the handbrake valve is set to the 'Parking Brake' position, the handbrake valve continuously leaks air from the exhaust port. Generally, this is caused by the intake valve and valve seat of the valve not sealing properly, foreign objects between the valve and the valve seat, or damage to the intake valve seal. Replacing the intake valve seal with a repair kit can resolve the issue.
During parking brake operation, a leaking handbrake valve does not cause other faults. However, when the handbrake valve handle is set to the 'Driving' position, a leaking handbrake valve can cause the car's rear axle wheels to 'lock' while driving. This is usually due to poor sealing between the valve stem of the handbrake valve and the air valve. Clearly, the reason for poor sealing at the exhaust port may be damage to the seal, or due to foreign objects or oil dirt between the valve stem and the air valve preventing proper closure. Disassembling to clean or replacing the intake valve seal can eliminate the fault.
2. Handbrake air reservoir takes too long to charge
Before starting the vehicle, the main brake air reservoir should first be fully pressurized. When the warning light goes out and the buzzer stops sounding, it indicates that the main brakes (front brake reservoir and (middle) rear brake reservoir) have reached sufficient pressure. At this time, if the handbrake valve is set to the 'Drive' position and the handbrake low air pressure warning light turns on, it means that the handbrake reservoir pressure is insufficient and the spring brake chamber has not fully released the brakes. If the vehicle is forced to start under this condition, the (middle) rear axle may experience brake 'drag.' Therefore, the vehicle should only start after the warning light goes out.
Under normal circumstances, after the main brake air reservoir is fully charged (after the main brake low-pressure warning light goes out), the handbrake air reservoir will also quickly reach full pressure (the handbrake low air pressure warning light goes out). If this charging time is too long (the handbrake low air pressure warning light does not go out for a long time), it indicates a problem with the brake valve (also called a relief valve) that connects the (middle) rear brake circuit and the handbrake circuit. The brake valve is a one-way relief valve that should open to quickly charge the handbrake circuit when the (middle) rear brake circuit pressure reaches 6.5 bar. If this pressure is set too high and the valve is stuck (or frozen) and does not open at all, it will cause excessively long handbrake circuit charging. Disassembling and adjusting this valve can eliminate the fault.
3. Air leakage in the spring energy storage chamber
Damage or tearing of the piston seal ring in the spring energy storage chamber, or scratches in the chamber cylinder, can all cause air leakage in the chamber. Since the spring energy storage brake chambers of the middle and rear axle wheels are all connected in the air circuit, as long as one chamber leaks, it will cause a drop in air pressure in all chambers, resulting in the middle and rear axle wheels being 'locked' during driving. When such a fault occurs, the leaking brake chamber needs to be disassembled and repaired. Disassembly and installation of the spring energy storage brake chamber must be carried out on a press to ensure safety.
4. Handbrake Relay Valve Air Leakage
When the vehicle is in the parking brake mode, air leakage from the relay valve will not cause a malfunction, which is obviously caused by damage to the sealing component of the brake valve's intake valve or by foreign objects or impurities between the valve and the valve seat, resulting in inadequate valve closure.
When the vehicle is in motion and the relay valve continuously leaks air from the exhaust port, it is obviously due to improper sealing between the exhaust valve and the piston. This will cause insufficient air pressure in the spring energy storage brake chamber, resulting in a malfunction where the service brake is excessively tight.
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