How To Bleed ABS (Anti-Lock Brakes)

If you have any problems with your break systems, like callipers or wheel cylinders, then the brake systems must be bled to remove the air to ensure that the brake pedal remains firm. If you get air trapped in you system braking becomes less solid and pressure to the pedal will provide soft braking, which can be quite dangerous, increasing the cars stopping distance. Firstly ALWAYS read your cars handbook and whatever information you can get about it before trying! a lot of good car repair and service handbooks can be found at charity shops and second hand book stores, well worth it.

Good diagram of location and basic workings of the braking systems of a standard car

Bleeding is a fairly simple operation on most vehicles, assuming no air bubbles have found there way into the ABS modulator assembly. The air in the system can be compressed, so when brakes are applied, the air must be compressed first before the liquid can slow the car, hence the feeling of soft brakes.

Tool exist especially to bleed braking systems, and it can be done fairly simply with a power bleeder, injecting tool or vacuum bleeder. All of these systems are equally effective, the idea is to flush the air out of the systems by pumping them with fluid.

So where do you start? The common place to begin bleeding your brakes is to begin with the ones furthest from the master cylinder, then the set on the same hydraulic circuit. You then follow this ending with the closest to the master cylinder. These solutions are fine, assuming you either just want to bleed you brakes to remove air bubbles, or you need to replace any of the system components which come after the modulator; calipers, wheel cylinders, brake lines or brake hoses. But if you need to deal with a component which is upstream from the modulator then the operation is slightly more difficult, although the above method will work, it is not 100% effective on the parts before (and including) the modulator.

The modulator has a lot of little places which air can become trapped in small cracks, and flushing it out has no effect, to solve this, you will need to consult a mechanic from a garage which specialises in your car, or find out exactly how to do it for your exact model, as the systems can be very different from car to car.

The modulator can contain 8 - 10 Anti-lock or traction control valves, aswell as other dead end ports and check valves. Some cars have special bleed screws built into the system which make this whole process a lot easier, allowing the air out of all the trapped areas. Others do not have bleed screws and needs a scan tool, which can cycle through the valve system whilst you bleed the mechanism, allowing all of the air to escape

If you are not experienced with cars and mechanics, do not try this! you can make it worse and then end up spending alot more money than you previously had to with a qualified mechanic. The best advice i can give you is to always read the book on your cars systems before trying ANY repairs yourself!