As a backyard mechanic this issue had me stumped like no other. I originally googled this issue with the words” brake goes to floor”, “spongy brakes” and it came up with thousands of links, but the technical term is “low brake”.

Here is my story:

The problem was very gradual and maybe taking a couple years to fully develop. I first changed the front brake pads, but no change. I then bled the brakes, but no change.

My dreaded yearly inspection was around the corner. Any of you living in New Jersey, knows what I’m talking about. Depending on what day you go, where you go, who you get and time of day, could be critical. Heck, even what you wear could matter. And then there is the waiting. In the old days, it was hours. I wasted many hours at the DMV that I will never get back. Now it has been reduced to about 60 minutes from start to finish. But it still matters when you go, where you go, who you get and how you do it if you want to pass.

Anyways, I had to pick up the pace because I would never pass with the brakes the way they were.

Since it was a while since I replaced the rear brakes, I went for it, but still no change. After consulting friends and the internet, I narrowed it down to the master cylinder. After replacing the master cylinder (bench bleeding included) the low brake situation was even worse. So worse that it took little effort to hit the floor with the pedal.

I bled the system with my wife at the wheel pumping and using 2 new bottles of fluid, but no change what so ever.

During the bleed, I checked for leaks or wetness and there was none

The back brakes had some movement when pressed, but not much on the fronts.

Adjusted the rear brakes by turning the “star” to where the wheel almost drags, but no change.

I bled the brakes again, but this time purchased a Mityvac 7000 from Sears for $40

With the pump, I sucked through about 2 bottles of fluid total for all wheels. Air bubbles were present and could not get rid of them. Finding no help on the Mityvac website and nothing on the internet, I figured this was a flaw and kept going. Finally on the last wheel, I discovered that the adapter that came with the Mityvac and goes on the bleeder valve was letting air into the bleeding system. That’s what was causing the air bubbles. I disconnected the adapter and put some clear rubber tube on the valve to the pump and voila, no bubbles, but still ……no change.

Thinking maybe I made a mistake, I took out the master cylinder again; bench bled and installed…….no change.

Also adjusted the brake booster push rod before the install, but ……..no change.

Looked at the freeplay and reserve in the manual, but had a hunch that was a waste of time.

There are no apparent leaks and the master cylinder has a constant level.

My next steps:

Remove the lines, plug up master cylinder and apply brakes. If no low brake then the MC is okay.

Bleed again with a fresh bottle using the pump.

During the bleed and while at each wheel, check:

The movement of the pistons, calipers, slides, pads, etc when brakes are pumped.

Could be a bad caliper piston. Look to see if there is clearance and movement.

Could be the flex hoses. Look for cracks. Personally I think this is a long shot but check anyways.

Could be a pad that is not on right.

Could be a sliding pin. Another long shot, but check movement. Maybe lubricate?

Double check for leaks

Adjust back brakes again

Note clearance between rotors, pads and piston.

Check into the “line lock “method of isolating the issue, by clamping the flexible hose at each wheel. Need a strong enough clamp.

Links:

Saturday Mechanic: Dealing With A Low Brake Pedal - Popular Mechanics