The brake system is designed to reduce speed and stop the vehicle. It also helps keep the car still when the engine is not working. This system requires regular service, which includes the “bleeding” procedure.
As soon as the brake pedal in your car has gone soft over time or your brakes don't feel as tight and precise as they used to, you might need to bleed your brake fluid. After all, the brake fluid in your car collects contaminants and degrades over time, losing its effectiveness.
So, let’s get into bleeding and discuss how things work.
First, let’s cover the basics and focus on how exactly the brake system works. This is essential due to the nature of the procedure.
The brake system consists of an actuator and brake mechanism. The service brake system actuator works as follows. The driver presses the brake pedal, and then the force is transmitted through the vacuum booster to the brake master cylinder. The brake cylinder pumps brake fluid through a system of lines (pipes) to the wheel brake cylinders. The fluid pressure in the wheel (service) brake cylinder actuates the brakes − disc or drum brakes. The vehicle slows down or stops.
Modern cars are equipped with a well-thought-out and effective brake system comprising service and parking brakes. Service brakes include four brake mechanisms and a hydraulic drive with split circuits. The hydraulic drive, which includes a vacuum booster and pressure regulator, ensures equal pressure across the circuits in the vehicle's braking system.
The pressure in the brake system is provided by different types of actuators: mechanical, hydraulic, pneumatic, or combined. But it does not make much difference, as the principle of air removal from the brake system is the same except for some minor details when pumping brakes with ABS.
How can air get into an airtight brake system? There are several possibilities, and even daily preventive inspections of the brake mechanisms and pipelines cannot guarantee a permanently airless state of the system.
Leaking brake systems can occur due to faulty connections when repairing or replacing parts, assembling, and replacing brake fluid. This is absolutely normal, but the main thing is to pump the entire brake system or an individual circuit.
Before bleeding, prepare clean brake fluid by pouring it into a plastic or transparent glass container (about 0.42-0.63 pints will be enough). Then, get a hose to the diameter of the fittings to remove the air and wrenches of appropriate size.
Make sure there is no brake fluid leakage anywhere in the drive units and pipelines of the system by visual inspection. Then, pour the manufacturer-recommended brake fluid into the tank to the “max” mark.
Bleeding is performed when pumping a single circuit. But if you want air removed from other brakes, just follow the steps above, and you should be all set.
Air removal (pumping) of the brake system starts at the farthest wheel from the brake master cylinder. For example, right rear − left rear − right front − left front.
After bleeding the brake system, test the pedal stroke. If it has the stroke you are accustomed to, you have done everything correctly. If it is still soft, you should either recirculate or have the brake pads, and disc checked.
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