What Causes Air Brake Lock-Up?
2 Answers
Brake lock-up mainly occurs due to the following reasons: the brake master cylinder has too little or no clearance; a faulty vacuum booster can also cause brake lock-up; the brake master cylinder is stuck; the brake fluid line is blocked, preventing fluid from returning; or the brake caliper is stuck. Below are the classifications of brake lock-up: 1. Brake lock-up caused by the brake caliper not retracting: Simply put, even when the brake pedal is not pressed, you can still feel significant resistance from the vehicle. In severe cases, abnormal noises may occur, or the wheel may even lock up. If the brake caliper is internally corroded due to not changing the brake fluid for a long time, it can be repaired by sanding with sandpaper and applying grease. If the caliper itself is faulty, it may need to be replaced directly. 2. Static wheel lock-up after parking: The vehicle is parked statically and locks up after sitting overnight. This phenomenon often occurs in vehicles with drum brakes on the rear wheels. The friction pads are semi-metallic-based brake pads, and the brake drum is made of cast iron. When the parking brake is engaged, the brake pads and drum are tightly pressed together. If exposed to water, the metal can oxidize and rust, causing adhesion. The solution is to spray rust remover or sand with sandpaper.
From my years of experience dealing with large vehicles, brake lock-up with air brakes is quite common and mainly stems from issues in the air pressure system or mechanical components. Insufficient air pressure leads to inadequate braking force, making it prone to lock-up during sudden braking; conversely, excessive air pressure causes uneven distribution, directly locking the wheels. Stuck valves or air hose leaks are often the culprits—for example, pipes freezing and blocking airflow in cold weather. Worn brake pads or faulty wheel cylinders can also create excessive friction, causing instant lock-up. Another critical factor is routine maintenance, such as dust buildup in valves or frequent hard braking overloading the system. Air brakes are more prone to issues than hydraulic systems because air responds slower and is less stable. I recommend owners regularly check the air pressure gauge, listen for any air leaks, and clean air hose debris every six months—safety is paramount to avoid accidents.
