Replaced pads and rotors, brake pedal sinking to floor now?!?

My brother-in-law had the little to no brake and couldn't figure it out. I went over and took 1 look and saw the bleeder screws at the bottom of the caliper. we reversed the drivers side and the passengers side got the bleeder screws on top and all was well.

Funny thing is he knows better and just didn't see it. Sometimes it is the obvious and you just don't see it.

Change the brake hoses.

Trainmaster said:

Change the brake hoses.

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Just got them today so I'll report back tonight!

We changed the hoses and calipers tonight and did another bleed (ABS system first, then another manual bleed) and nothing changed with the pedal pressure.

UniqueTII said:

We changed the hoses and calipers tonight and did another bleed (ABS system first, then another manual bleed) and nothing changed with the pedal pressure.

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My 07 the mechanic need a scan tool for the ABS to activate the valves. Can you get the ABS to activate while driving? This may cycle the pump. I found this it is a E350 but may pertain to this issue.


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outdare said:

My 07 the mechanic need a scan tool for the ABS to activate the valves. Can you get the ABS to activate while driving? This may cycle the pump. I found this it is a E350 but may pertain to this issue.


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Click to expand...

The Snap-On scanner will activate the valves for each wheel, which is what we used. I'm thinking the Hydraulic Control Unit is having issues so I have a low mile used one on the way. The only thing left is the booster but I don't know how that would cause this symptom.

I have to agree with retiredusps on the idea that the master cylinder is leaking internally. There is no other place in the system that a leak could occur that could cause the pedal to go down without leaking outside of the system. Fluid under pressure causes the pistons at the wheels to move but the o-rings in the master cylinder cannot keep the fluid from seeping back past them and returning to the reservoir. Usually, in a two reservoir system this doesn't happen because one system doesn't allow the fluid to return, but one system would still leak back taking the pressure off the affected brakes while the other one maintained it's pressure. Once the second system fails, it then behaves like a single reservoir system allowing the pedal to sink to the floor because of the internal leak.

Where are you clamping the front lines at?

Based on what I've read, it sounds like you have a problem at the caliper(s). I say this because you state that the pedal feels good when you clamp the front lines. At that point, you've virtually eliminated all of the other components as possible sources of the issue. The master cylinder holds pressure. The rear brakes hold pressure. The ABS holds pressure. At that point, all you have left is the front lines and calipers.

I would suspect the lines (which you have ordered). I had issues with mine where they would bleed ok and looked fine, but must have collapsed internally. New front lines fixed it up right.

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Thanks for the new responses! I do have a spare (used) master cylinder I can throw on there, but I didn't suspect the MC because it held pressure when plugged. I did see someone test one with only one port plugged, though, so maybe I should try that.

I replaced the front lines and calipers, followed by a full bleed including the ABS system, and nothing changed. I just swapped out the ABS HCM but haven't been able to do a full bleed yet, so we'll see if that helps.