Why it's Important to bleed your brakes
Brake bleeding is the process of purging air bubbles from hydraulic brake systems. The procedure is essential as the air bubbles are made up of compressible gas that reduces the pressure produced by the hydraulic system. Air can enter the brake system during specific types of servicing or when there is an air leak. Constant slamming of the brakes and worn out pads can also cause air to enter the braking system. Small bubbles of air develop a spongy feeling when stepping on the pedal while large amounts of air lead to braking failure. Usually, the process involves forcing bubble-free brake fluid into the system from the master cylinder to the drum brakes or disc brakes. Brakes should be bled every two or three years to keep a healthy brake system at optimal performance. Here is a look at the various brake bleeding techniques used.
What are Vacuum Brake Bleeders?
A vacuum pump is connected to an open bleeder valve, and the fluid extracted using a pump to remove the bubbles. This method of brake bleeding can be performed by one person using vacuum bleeders that utilise shop air pressure to suck the fluid from the bleeder. However, vacuum brake bleeding has certain drawbacks in that it can cause air to enter the system, leading to more problems.
What are Pressure Pumpers?
In this case, a pressure pump is connected to the master cylinder and the bleeder valves opened in a sequence until all the air in the fluid is pumped out. Special pumps use a method that ensures the brake fluid remains full during the bleeding process. Pressure bleeding units may be used to pressurise the fluid in the reservoir. The beauty of the method is that it is fast and only requires one person to perform the job.
Additionally, it is ideal for older cars that have had little maintenance. With pressure bleeding, the master cylinder does not need to be stroked to push the fluid into the system. Stroking of the pedals to the floor causes the piston to move deep into the master cylinder, creating further damage. The seals may also pick up dirt and get damaged.
What is Bench Bleeding
When the master cylinder is replaced, it has to be bench bled before installation. This is because air gets trapped in the cylinder and bench bleeding is the easiest way of removing it. The fluid reservoir is filled with brake fluid and return hoses attached to the outlet ports to ensure the fluid is recycled into the reservoir while stroking the push rod. If you can’t access return pipes, you can put your finger on the outlet ports to stroke the cylinder in the vice as the piston returns. Keep doing this until there is a steady flow of fluid from each port, and then, fit the plugs in the ports and the cylinder to the vehicle. Next, you need to bleed the pipes on the master cylinder to remove air from the highest point in the system. This is achieved by cracking all the outlet pipes and depressing the pedal. Be sure to bleed the pipes before releasing the pedal and repeat the procedure until there is no air in the system.
What is Manual Bleeding of Brakes?
In this method, the master cylinder is used as a pump to remove air from the brake fluid. It is a two-man operation; one person opens and closes the pedal and the other pumps the pedal slowly. Brake bleeding is performed using a piece of clear plastic hose. One end is inserted into the fluid to prevent air from getting into the system when the bleeder is opened. The bleeder screw remains closed at the end of every stroke before releasing the pedal to ensure no air gets sucked back into the system.
Other Brake Bleeding Techniques
- Gravity bleeders:
It is the simplest method of replacing automotive brake fluid and relies on the concept of gravity. Gravity bleeding may not be as effective as other bleeding methods.
- Pump and hold:
the process involves pressing the brake pedal while opening one bleed screw at a time to allow air to escape. The bleed screw should be closed before releasing the pedal. Alternatively, you can fit a one-way valve.
- Reverse bleeders:
a pump is used to force out the fluid from the bleeder valve to the master cylinder. The idea here is that air rises in liquid and escapes from the braking system.