2012 Escape XLT 2.5L - 180k miles

Hi All.

I hope some of you can help me.
I was driving my daughter's car this morning and found that one of the caliper pistons was seized. Since the car has 180k miles on it I decided to replace both front calipers, rotors, pads, and the flex brake lines. everything went smoothly without any issues.
I did bleed the brakes afterward, utilizing the "manual method", where my daughter was squeezing the brake pedal (engine off) while I was at the bleeding screws. The fluid reservoir never run below min. Yes, I used new DOT3 brake fluid.

The issue is that when the engine is running the brake pedal is extremely soft and goes to the floor before some brake pressure is applied.
I checked for any leaks, there are none.
I did bleed the two front calipers again, no air is coming out. When the engine is off, the brake pedal compresses quickly and is solid after a few inches.
However, when the engine is one, the problem is present.

Any ideas?
Thanks a lot in advance.

 

Unless the master cyl is new, anytime the brake pedal goes to the floor the rubber cups in the master get scored by the abrasive sediment in the bore of the master cyl.

This results in INTERNAL leakage, and the master cyl now needs to be replaced. Don't forget to bench bleed the master BEFORE installation.

 

Thanks Hanky.

Somehow I am curious why would the master cylinder leak when the pressure on the pedal is firm and stable? wouldn't it move when pressed in case of a leak?

However, I change the master cylinder, which was this afternoon and bench bled the master cylinder and afterward I bled the entire system twice.
I also bled the ABS pump twice (I have the tool for it).

No change, whatsoever. When the engine is shutoff the pedal is firm and as soon as I turn on the engine the pedal is soft and can be pressed to the floor.

Any more ideas, before I rip out the ABS pump module?

 

You might consider trying to stop the vehicle while driving and see if it really requires all the pressure you are applying while parked.