Expert: Rob Painter - 1/19/2011

Question
Hi, recently I've been having issues with my Cadillac's brakes going all the way to the floor.  I've had someone do multiple repairs to get it working, but after trying what appears to be everything, the person is stumped.  New brake pads were put on, the brake lines on both sides were even replaced (due to leaks in them), the Master Cylinder was replaced, and the Brake Booster was even replaced...yet they still go all the way to the floor.

Does anyone know what the problem could be?

Answer
Hello,

Here is a very difficult question to answer because you say the brake lines were replaced due to having holes and pads were replaced. You did not mention any other replacement parts.

Now, you have to separate systems-front-rear. A proportioning valve in between, controls the braking between front and rear.

I also have no idea as to the experience of your "mechanic", or the equipment he has. I find it a little strange that an experienced technician could not properly diagnose the issue after replacing the lines and the pads. Were the calipers replaced? Were the rotors replaced? If so, are they the correct rotors? If the rotors were not replaced and all that was replaced was pads, even with new pads, the calipers could be extended so much that you have no pedal. Was a pressure bleeder used? Some of these cars, especially with anti-lock 4 wheel discs, do not respond to gravity bleeding.

Proportioning valve could be stuck. I never ran into it on GMs, but I remember Fords had a special needle to reset the valve.

If your brake lines had holes in them, chances you are from one of those rusty states that use road salt, or this thing parked on the grass for years without being moved. Are you absolutely sure the caliper boots are not leaking? The gaskets from the brake hoses to the calipers?

You cannot just change pads. Rotors have to be machined, but usually they can't be because they will go under tolerance and new rotors must be installed. Calipers should be rebuilt or replaced due to internal leakage. Possibly when the pistons were pressed in to install pads, boots could have pinched and are leaking.

Assuming the calipers, rotors were changed with the brake pads, and assuming there are no leaks, you will probably need someone with a pressure bleeder, but be aware you cannot take short cuts on the brake system and expect a good pedal height.

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