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Brake Bleeding Methods
1. Brake Bleeading
Brake Bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for purging, where the old fluid is replaced with new fluid, which is necessary maintenance.
Brake fluid is toxic, and must be handled carefully and disposed of properly. Most cars use DOT 3 or 4 brake fluids, which may be mixed, but DOT 5 is silicone-based and not compatible with DOT 3 or 4. Most types of brake fluid harm automotive paint and plastics on contact, so special care must be taken when using this fluid: any spills must be immediately cleaned up. Brake fluid is water-soluble so it may be rinsed off with water.
The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the master cylinder(s) to the calipers of disc brakes (or the wheel cylinders of drum brakes), but in certain cases in the opposite direction. A brake bleed screw is normally mounted at the highest point on each cylinder or caliper.
2. Vacuum Bleading Method
Vacuum Bleeding uses a pump to pull fluid and air out of the bleeder screw. It is fairly simple and is an effective operation.
* Advantages: Vacuum bleeding method is very simple and will work on most vehicles with a bleed screw. Most people are familiar with this type of bleeding method because it is so common and ease to use.
* Disadvantages: Vacuum bleeding is the least effective bleeding technique. It should really only be used in combination with another brake bleeding method. Some vehicle manufacturers do not recommend vacuum bleeding. One of the primary problems is air leaking around the bleed screw threads.
3. Pressure Brake Bleeding Method
Pressure Brake Bleeding normally uses a pressurized tank of brake fluid to cause fluid to flow through the bleeder screws. Pressure bleeding has the advantage of being a one-man operation, and is an effective method of removing air and flushing the hydraulic circuits.
* Advantages: Pressure bleeding method is a very common and effective bleeding technique. It keeps the brake system under pressure and is the best brake bleeding method for flushing dirty fluid from the system.
* Disadvantages: Most vehicles may require special adapters to seal the master cylinder reservoir for pressure bleeding. Usually is used a universal port adapter that will work on most master cylinders. The set up time is much longer than reverse or vacuum bleeding
4. Reverse Brake Bleeding Method
Reverse Brake Bleeding injects fluid at the low points, the slave bleeder valves. Reverse Bleeding takes advantage of the “laws of Physics” air rises in fluid. The complete system is bled by forcing the air up and out the master cylinder reservoir. The brake fluid then fills the reservoir.
* Advantages: Reverse bleeding method is the absolute best single brake bleeding method to use. It is the most effective at removing trapped air. It works well with ABS equipped vehicles as well as any vehicle with a bleed screw. It is very quick, the fastest of any bleeding method.
* Disadvantages: The brake system should be flushed prior to reverse bleeding. The bleed screw must not be plugged for reverse bleeding to work. Also, must be careful not to overflow the brake fluid reservoir.
