This tech tip is about the brakes and ABS system on our vehicles. Most of us know how the brakes work, but I am going to go over how the ABS system works and what you can do to keep it running smoothly.
The ABS system doesn't do a single thing until you need it. It's just sitting there waiting for something to happen. Then when it does, it takes control and helps you maintain control by pulsing the brakes and keeping the tires from skidding. In the biz, this is called an ABS event. The system watches the wheels through wheel speed sensors. It compares this wheel speed information and when it sees you jump down on the brakes it waits for a wheel to lock up. It senses the individual wheel slowing down and begins an ABS event. The hydraulic control unit uses a valve block and a hydraulic pump to control the fluid flow to the brake calipers. In an ABS event, it closes an isolation valve to prevent any more fluid pressure from getting to the caliper. Next, it opens a dump valve and allows the pressure in the caliper to vent back to the master cylinder. This releases the brake and the wheel begins to rotate again. At this point, it closes the dump valve and opens the isolation valve and once again lets brake pressure from the hydraulic pump motor go to the caliper. This describes one complete cycle of an ABS event. The important thing to know is that this happens 36 times per second.
Another thing to know is that the fluid in the hydraulic control unit
just sits there until you need it. This also means that the fluid there
can get stagnant. Doug's first tech tip of the day is to find a dirt or
gravel road with no traffic. Get going at a good clip and jump down on
the brakes. This will easily induce an ABS event. The loose surface will
let the brakes lock up and trigger the ABS to cycle its valves and run
its pumps and motors circulating the fluid within the system. This should be done about every month or so, just to keep things circulated. Remember that brake fluid is hydroscopic and absorbs water. Water can settle in places that you'd least expect. Cycling the ABS keeps the fluids in the HCU from getting stale.
One more thing to help your brakes last longer. When coming to a stop, be sure and stop short a few feet. As you sit and wait for the light to change (or whatever), let the truck creep forward a few inches. Remember that the brakes turn kenetic energy into heat energy. Simply put, the rotors job is to get hot and then dissipate that heat. If you stop the vehicle and hold it still, the pads hold heat in the rotor at one point. If you let it creep forward just a few inches, you move the rotor from under the pads. This lets that part of the rotor cool. Keep doing that until the light changes and your rotors will stay straight longer.
If you have a Super Duty truck more than likely most of you reading this will have had problems with warpage. The problem isn't the truck, it's the stock parts that came on the truck. Our brake kit consists of a pair of Italian rotors that are grooved and a high quality set of ceramic composite pads. These units have out performed anything else that I've seen. They stay straight and last a long time. I'll still push the exhaust brakes, but these kits are easy to install and should be priced right too.