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Process of Elimination (another brake issue thread)

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#1
So I've been having a small issue since I've had the car that the top inch or so of brake pedal travel is soft. You pump them, they get hard, then slowly sink an inch or so. The catch is, the car still slows and stops pretty reasonably even in that inch of mush. Knowing the car's history, I knew there was a good chance for an improper ABS bleed, or the possibility of a damaged master cylinder from dry bleed.
And so then I did an all around vacuum bleed, while also cycling the ABS with Forscan. Speaking of Forscan, if anyone has detailed instructions they can point me to (besides the on screen prompt of "push pedal" and "release"), that'd be great, unless it really is just press and release. I saw Fords bleed procedure, but for the ABS they just say refer to service manual... Bleeding did nothing, and I don't want a pressure bleeder, a pressurized tank and lines full of brake fluid scares me. Vacuum only. Also did pads and rotors, no better.
My next step was to experiment a little. Does the pedal change with the handbrake on? No. How about with the hose pinched? No. Now here's the interesting one. Does it change with the hill start activated? YES! Rock hard. Hill start uses ABS as a kind of line lock, closing off a valve prior to the air bubble, yes? Therefore the pedal feel? So here's what I'm asking after reading the backstory. Does anyone agree with me that because of the difference of pedal with the hill start activated, that the issue is NOT the master cylinder? I know it could still be the ABS module itself, but one thing at a time. I feel like knowing this, it'd be worth paying Ford to do a professional bleed job, knowing the money/time is not wasted. If anyone has methods of isolating components, that'd be appreciated too. Thanks.
 

Intuit

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#2
Did you try bleeding with the engine running? (which means vacuum assist at the pedal = on) With no vacuum assist from the engine running, the pedal can be rock hard. But add vacuum assist, the pedal could instantly go from hard to mushy. If the manual warns against this, disregard my comments.

The motorcycle doesn't have ABS but recently went through some bleed issues with it. I'd get it really hard and by the next day, mushy again. (there's no vacuum assist with motorcycles) Bought a vacuum assisted bleader (it actually employs a normal air-compressor and develops vacuum using the Venturi Effect) and proceeded to waste a can of the expensive low viscosity brake fluid bleeding every microbubble out of the thing. Even rebuilt the master cylinder. Longer story short, using 150 PSI compressed air blowgun, I discovered that the bleed screws were leaking very tiny amounts of fluid. It wasn't really leaking this fluid, more than it was sucking in air... tiny amounts with each release of the brake lever. Using an appropriately angled and sized screwdriver PHZ head, I ground down the caliper's bleed screw seats.

Having recently replaced the front pads on my car, the additional pedal travel I suspect is only pads. That pedal travel has cut considerably as the pads have embedded into the rotors. (taken on its surface shape) There was relatively little difference in pedal travel when replacing the rear pads.
 

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