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2026
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The brakes are not effective; it's time to replace the brake caliper with a new one.
Medium and heavy trucks generally use compressed air as the braking medium. The air compressor pumps air into the air tank. With each brake application, the compressed air releases its force onto the brake cylinder, pushing the brake shoes to brake. In addition to tire friction and sufficient air pressure, the effectiveness of braking also depends on how much output the brake cylinder can provide.
● Brake chamber, technically called brake cylinder
Small cars rely on the vacuum created by the engine to drive the master cylinder diaphragm (cup), which then pushes hydraulic fluid to move the caliper piston. Trucks, on the other hand, rely on compressed air pressure to drive the diaphragm inside the brake slave cylinder, which in turn pushes the push rod.
The most common type on trucks is the dual-chamber brake air chamber, whose standard name is the spring brake air chamber. This type of air chamber combines the functions of service brakes and parking brakes and is widely used on drive axles and trailer axles.
Although the braking mediums are different, structurally, the two have similarities. The brake slave cylinder structure on trucks is similar to the master cylinder in small cars—they both rely on air pressure (vacuum) to push the diaphragm inside the cylinder to generate thrust.
From the above sectional view of the double-chamber brake air chamber, it can be seen that the double-chamber brake air chamber has two air ports, which are connected to the service chamber and the parking chamber, respectively.
Here, you only need to remember one point: service braking is 'air-on braking,' and parking braking is 'air-off braking.' The springs inside the service chamber and the parking chamber correspond to this.
Service Brake
For example, during service braking, air enters the service brake chamber through port 11, pushing the diaphragm and compressing the spring, thereby causing the vehicle to brake.
Parking brake
When the parking brake is applied, the air in the parking chamber is expelled, and the push rod is driven by an internal spring, thereby achieving parking braking.
Releasing the Parking Brake
Releasing the parking brake is exactly the opposite. Air enters the parking brake chamber through port 12, and the air pushes the diaphragm to compress the spring, thereby releasing the parking brake.
Now comes the key point: since the movement relies on the air pushing the diaphragm, the quality of the diaphragm must be particularly reliable.
If the diaphragm leaks or is damaged, the consequence will be insufficient force from the wheel cylinder, resulting in weak braking performance or even brake failure during driving.
Meanwhile, the parking brake will continue to operate, causing dragging.
If the spring in the service chamber is of poor quality and has weak return ability, it will cause vehicle dragging, while if the spring in the parking chamber is of too poor quality, it will reduce the vehicle's parking brake capability, leading to serious accidents such as rolling.
In short, this thing, no part of it can break. If one part breaks, it affects the whole system—it either can't stop or can't move. Therefore, you need a reliable spring brake air chamber.
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