Spring brakes, like drum brakes and disc brakes require frequent maintenance in order to ensure their proper working order. Spring-set brakes are installed as parking brakes on vehicles that use air brakes. The spring parking brake is applied by spring and retracted by air pressure. This is the opposite of the service brakes on the same vehicles which are applied with air pressure and released by a spring. Because the two types are connected through the same linkage and have attached chambers, in order to have an effective spring brake system, the service brakes must be in working order.
Spring brakes are meant to be for parking, but in the event of an air pressure loss, they can help stop the vehicle. Replacing spring brakes requires specialized knowledge, for removal can be very dangerous if you are not careful.
Tools and Materials
- Caging wrench
- Wheel blocks
Step 1: Access the Caging Bolt
The caging bolt is a piece of metal that runs through both the spring brake and the service brake chambers. It must be turned in order to compress the spring. This is absolutely imperative. The spring is under extremely high pressure, and disassembly should never be attempted without compressing the spring. Different air brake systems may have different ways to get to the bolt. In some cases, there is a dust boot that must first be removed. Other systems require you to remove a lock plate to access the bolt. Check the air brake manual for the rig first.
Step 2: Block the Wheels
Before you cage the parking brake spring, put blocks under the wheels. This spring may have to be caged when the rig has lost air pressure. In order to tow the vehicle, the parking brake must be released, so always ensure the vehicle won't move.
Step 3: Cage the Bolt
On the body of the parking brake chamber there should be specific instructions on exactly how to cage the bolt for that system. Follow these carefully for again, the spring is under tremendous pressure and could seriously injure you. Once the spring has been compressed by caging the bolt, it is safe to disassemble the chamber to replace the spring.
Step 4: Disassembly
Disassembly of the brake chamber should only be done by a qualified technician. The spring is loaded with thousands of pounds of pressure and can be deadly if released unintentionally. Once you have caged the bolt, the parking brake is released and you can have the rig towed if need be. Stopping at that point is a wise idea unless you have been trained to disassemble the brake chambers.
Replacing a spring parking brake on an air brake system is a complicated job because it requires such specialized knowledge. Written on the chamber are instructions how to properly cage or compress the spring by tightening the caging bolt. If your rig has lost air pressure and has to be towed, doing this releases the parking brake so it can be. Replacement of the spring, however, if that's what needs to be done, is a job for a certified air brake technician.
Related Questions and AnswersWhat are the Various Types of Car Brakes?
There are two basic types of car brakes. These are the disc brake and the drum brake. The disc brake uses a caliper with a piston that causes two pads two squeeze a rotating rotor to slow and stop the vehicle. Drum brakes use a wheel cylinder in which fluid pressure presses outward on two brake shoes that press against an outer rotating drum to slow and stop the vehicle. Car brakes can be further broken down into power assisted and non-power assisted. Although unless you have a much older car, you probably won't see non-power assisted brakes. There are also two types of brake actuating systems. Air brakes, which are found in larger vehicles, and hydraulic brakes, which are found in most cars and pickup trucks. To see diagrams and descriptions of the two basic types of brakes, click here.