The function of the rear brake assembly of the car
The function of the rear brake assembly of a car is to handle the braking of the rear wheels, allowing the moving vehicle to slow down or stop as required, while also cooperating with the front wheels to maintain the stability of the vehicle.
Specifically, there are several aspects:
1. Main braking function: When the brake is pressed, the friction blocks of the rear brake pads will press against the brake discs or drums of the rear wheels, relying on friction to slow down the rear wheels, thereby making the entire vehicle slow down or stop.
2. Maintaining braking balance: The rear brake pads and front brake pads work together to distribute the braking force more reasonably among the four wheels, avoiding the vehicle's imbalance or skidding during emergency braking.
3. Auxiliary parking: Some models' parking brakes (hand brakes or electronic hand brakes) also achieve this through the rear brake pads, allowing the parked vehicle to remain stable on slopes or flat ground.
The braking force borne by the rear wheels is less than that of the front wheels, so the rear brake pads usually wear out more slowly and have a longer replacement cycle, typically around 6-100,000 kilometers, but this can vary depending on driving habits and road conditions.
It is generally composed of a steel backing (supporting framework), a heat insulation layer (to block heat), and a friction block (the part that directly generates friction). It is an expendable item, and when it wears out to the limit, it must be replaced; otherwise, it will affect the braking effect.
When the rear brake assembly of a car fails, the most typical manifestations are: brake not returning to position or returning slowly, abnormal wear, and abnormal noise. The core reason often lies not in the brake pads themselves, but in the calipers and return mechanisms.
Let's look at the main causes of failure:
1. Caliper piston jamming: This is the most common cause. The dust cover of the piston is damaged and gets wet, causing the piston to rust and get stuck in the cylinder hole. After releasing the brake, it cannot retract, and the brake pads remain in contact with the brake disc, resulting in continuous wear and overheating of the hub.
2. Guide pin jamming: In a floating caliper, the guide pins allow the caliper to slide. If the dust cover is damaged, the lubricating grease leaks out, gets wet, and rusts, causing the caliper not to return properly. This "stick" state is difficult to detect normally, but it will cause abnormal wear of the brake pads, such as the rear pads wearing out faster than the front pads.
3. Electronic hand brake mechanism problem: For rear calipers with electronic hand brakes, there is an additional motor and actuator, and the return is not as good as traditional hand brakes. The rear pads are often worn out first, which is very common.
4. Brake fluid problem: If the brake fluid is too dirty or has an excessive moisture content (up to 3%), it will cause the internal valve of the master cylinder to become stuck, affecting the return. It is recommended to replace DOT4 level brake fluid every 2 years or 40,000 kilometers.
How to self-check and handle:
1. Feel the temperature of the hub: After driving a section of road without frequently braking and stopping, stop and place your hand on the hub to feel the heat radiation. If one wheel is significantly hotter than the other three, that side is suspected of being sluggish.
2. Check the wear sequence: The front wheels bear most of the braking force. Normally, the front pads wear out first. If the rear pads wear out faster than the front pads, it can be concluded that there is a problem with the caliper or electronic hand brake mechanism.
3. Push the vehicle in neutral: On a flat surface, release the handbrake and let go of the clutch. A normal vehicle can be pushed by one person and roll for a while. If it is significantly difficult, it should be checked for sluggishness.
Braking not returning to position is not a minor issue. It will directly reduce the braking efficiency and increase the risk of rear-end collisions. If you smell a burnt odor while driving, you must immediately stop to check, and do not force the brake pedal to try to return it.
Maintenance suggestions and costs reference:
When repairing, there is a key pit to avoid: only replacing the pads, not repairing the calipers. This is most likely to recur. The correct approach is to remove the pads and check if the guide pins slide smoothly, if the dust covers are damaged, clean, remove rust, and reapply high-temperature-resistant caliper lubricating grease (silicone-based). If the covers are damaged, replace them directly, then check the piston return, and finally install the new pads.
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