Why Doesn't the Disc Brake Caliper Piston Retract?

[Olivia]

Disc brake seizure and failure to retract are caused by water entering the brake fluid, leading to rust on the caliper piston. Below are the reasons why the brake pedal becomes hard and difficult to press: 1. Vacuum booster issue: This situation definitely indicates a problem with the vacuum booster. Whether at low speed or not, under normal driving conditions, the negative pressure in the intake pipe should draw air into the vacuum booster. 2. Vacuum booster air leak: The vacuum booster is always in a state of energy storage. If the brake pedal becomes hard after one press, it might be due to too low speed and too high a gear, resulting in insufficient intake negative pressure to draw air. However, if the pedal is hard on the first press, it definitely means the vacuum booster is leaking air. 3. Hydraulic brake system: Because a hydraulic brake system is used. When the engine is off, the hydraulic pump driving the hydraulic brakes is not working, causing a sharp increase in brake resistance, which is reflected in the pedal becoming very heavy and hard.

[SanMila]

I encountered this situation when repairing my car before. The disc brake caliper piston not retracting is often due to dirt or rust jamming the internal structure of the piston, preventing it from flexibly expanding and contracting. If the brake fluid hasn't been changed for a long time, it absorbs moisture and thickens, forming impurities that block the oil circuit, or the sealing ring ages and leaks oil—these are all common issues. When the piston gets stuck, the vehicle may experience brake dragging, tire overheating or even smoking, a sharp increase in fuel consumption, and in severe cases, it may cause a fire or brake failure. For safety, don't force it to drive; go to a professional repair shop immediately for inspection. You might need to replace the piston or clean the entire caliper assembly. For regular maintenance, remember to change the brake fluid every two years to avoid small problems turning into big troubles.

[Espírito Santo]

Having worked with car disc brakes for years, I've found that pistons failing to retract are mostly caused by air bubbles in the system, deteriorated brake fluid, or corrosion/seizure on piston surfaces. This leads to sluggish brake response, pedal sticking, and high risk of hub overheating/deformation. During inspection, first release hydraulic pressure, then gently push the piston with tools to test mobility - if stuck, disassembly for rust removal or part replacement is needed. Worn seals are another major hazard; I recommend combining regular maintenance with brake fluid replacement to ensure clean, unobstructed hydraulic systems. Never tamper with hydraulic circuits yourself - complex operations require technicians with specialized equipment for safe handling, otherwise you risk damaging brake discs and incurring higher costs.

[MacSamantha]

My car once had this issue where the disc brake caliper piston got stuck and wouldn't retract, caused by rust and dirt buildup around the piston, plus old brake fluid. This led to the wheel locking up after braking, making driving laborious and even causing smoke. The real danger was the potential for accidents, so I immediately took it in for repairs where cleaning resolved the problem. I advise car owners not to delay if they encounter similar symptoms—a simple brake system inspection can prevent such failures, ensuring driving safety is paramount.

[Jordan]

As a cautious driver, I've noticed that piston failure to retract is often caused by seal wear or oil passage blockage, especially prone to rust and seizing in humid environments. This can lead to rapid brake disc wear and abnormal noises, sharply increasing repair costs. Professional bleeding, bubble removal, cleaning, or component replacement is required for repair—don't cut corners to save money. It's advisable to inspect the entire hydraulic circuit to prevent recurrence. Regular maintenance of brake fluid is a crucial step to extend brake system lifespan.