Low brake pedal

Hello my name is Dave.

First thing we need to find out is why the pedal went to the floor in the first place. If you have done a repair the required bleeding then we need to be sure that the bleeding process was successful. Does the pedal get firm and stay firm when you pump the pedal rapidly and hold it? If it does we should try bleeding the brakes again to be sure we have all the air out. If it doesn't we can usually skip the bleeding until we find the cause however if you get no pedal a lot of air in the system can make it very difficult to get the pedal to pump up Lets start with a bleeding method that takes the guess work out of the equation.

When bleeding this system the factory instructions call for unplugging the ABS module and this is usually the safest way to prevent it activating and aerating the fluid. When bleeding brakes we want to start with the wheel the furthest from the master cylinder. I like to use a small vacuum or washer hose, usually 3/16 around 3 feet long. I slide the hose over the bleeder after putting a wrench over the bleeder to loosen it. I then take a drink bottle and put a just enough brake fluid in it to cover the other end of the hose and then open the bleeder and have an assistant pump the pedal. You will see bubbles in the fluid at the bottom of the bottle, when the bubbles stop have them hold the pedal to the floor and close the bleeder.

Refill the master cylinder and move on to the wheel that is the next closest to the master cylinder, repeating the process in order working your way back to to the master cylinder, making sure the master cylinder never runs out of fluid. If the master cylinder runs out of fluid you will have to start over from the beginning.

If you haven't performed a repair that calls for bleeding the brakes then we need to find out why the pedal is sinking. Have you been losing any brake fluid? If you have we need to fine out where it is leaking. All you can do is pump the brakes sitting in still then inspect the entire brake system for leaking.

There are only a few other reasons a pedal will sink as you describe with out a visual leak, the most common is a faulty master cylinder however they will usually leak out of the back so first thing we want to look for is wetness and peeling paint on the booster at the back of the master cylinder, if you don't see these clues I would loosen the master cylinder and pull it out just enough to see if there is any fluid is in the front of the booster (you usually don't have to disconnect the brake lines)

Another cause can be a internally ruptured brake hose, there is one at each wheel feeding each caliper. Have an assistant pump the brakes repeatedly as fast as they can and watch each hose for swelling, if they have ruptured inside they will swell up when under pressure but go back down after the pressure has been taken away.

There is a small chance that the ABS module is causing this issue but that is very unusual and I feel confident we will find another cause.

Please keep us up to date on your progress and thank you for using 2CarPros!