What is the reason for no response when releasing the spring brake with a leaking four-way valve?
2 Answers
No response when releasing the spring brake with a leaking four-way valve may be due to reasons such as a ruptured brake chamber spring diaphragm or damaged air hose of the brake chamber. The specific details are as follows: Ruptured brake chamber spring diaphragm: Often, it is not due to a faulty relay valve. First, check the rear brake chamber. In many cases, it is caused by a ruptured brake chamber spring diaphragm or the presence of foreign objects. Damaged air hose of the brake chamber: You can unscrew the air hose connected to the brake chamber. The brake chamber air hose that releases air is the faulty one, and replacing a rubber hose will suffice. Introduction to spring brake: The spring brake method is mostly used in the parking brake systems of medium and large-sized vehicles. The parking brake system of such vehicles is usually in a braked state with a powerful spring. When the vehicle is to be driven, the driver releasing the parking brake is an action of air inflation. A certain air pressure must be reached to push open the spring, which means releasing the parking brake before driving. Conventional braking involves the parking brake locking the drive shaft, while the foot brake involves compressed air entering the brake chamber to lock the wheels. Working principle of spring brake: The air pump, driven by the engine, compresses air into high-pressure gas, which is stored in the air reservoir. One air reservoir can be connected to the master brake cylinder via piping. When the driver steps on the brake pedal, the upper air is opened first, and the high-pressure gas in the air reservoir is transmitted to the relay valve.
Yesterday my truck also experienced a situation where the spring brake didn't respond. It turned out to be caused by air leakage in the four-way valve. When releasing the handbrake, insufficient air pressure meant the spring chamber couldn't push the brake pads, making it impossible to unlock. First, check if the air pressure in the reservoir is normal - if it's below 4 kg, problems will occur. Then trace along the air lines to find leaks; common issues are aging/cracked valve connections or worn seals in the valve body itself. Last time for me, it was a deformed rubber ring in the connection - replacing it solved the problem immediately. Also, don't overlook possible relay valve failure; it controls airflow direction and if stuck can also cause spring brake failure. If you can't fix it yourself, go to a repair shop immediately - safety first.
