Inconsistent brake pedal

[MauiRoads]

In previous posts, mostly about FORScan individual component bleeding (https://www.fiestastforum.com/threads/how-to-bleed-brakes-with-forscan.29950/page-3) I thought a full FORScan bleed had solved my inconsistent brake pedal. Turns out, it reduced the inconsistency, but didn't eliminate it.

Sometimes, hot or cold, the pedal has little initial travel before reaching an acceptable firm feel. Sometimes, even seconds later, hot or cold, the pedal has more initial travel and and an unacceptable soft feel. I've tried all of the FORScan bleed functions and even got FORScan to send me the "European Version" with individual component bleeds (MC, ABS, individual calipers) without improvement. Since then, I installed StopTech slotted rotors and Porterfield R4-S pads, and cleaned and regreased caliper slide pins and pad sliders. While the R4-S pads greatly reduce the factory pads' initial grabbiness and are more linear, the inconsistent pedal remains.

I haven't tried the cruise-control switch, though I've never understood how that can affect brake performance...doesn't it just switch off the cruise control when you press the brake pedal?

Does this sound like a booster problem? I have no experience diagnosing those.

Any help would be appreciated.

 

[MauiRoads]

Has anyone else experienced this, or a similar brake problem?

 

[Intuit]

If the brake booster were leaking vacuum, the pedal would initially be hard and get softer. The more vacuum the engine pulls from the brake booster, the more assist it can provide. (to a point)

The brake booster does have a one-way valve that prevents it from leaking vacuum back into the intake. If this has a problem, you might theoretically end up with some of the symptoms you describe. But this problem would be dead obvious as you would have no brake assist before starting your car at the beginning of the day... your pedal would be hard as a rock. Vacuum is highest when your engine is running with the throttle plate closed.

Put all four wheels up in the air. Run the engine for a short while at idle. Go to each wheel and give it a roll. Apply and release the brake. Then repeat the prior test. They should all be similar resistance. Take the vehicle for a drive and perform some longer, harder stops to heat the brakes up nicely. Repeat the prior tests before they have much of a chance to cool. It's common to have caliper slide mount(s) that only lock up when hot. https://www.fiestastforum.com/threads/caliper-slide-mounts-the-permanent-fix.29023/

 

[MauiRoads]

Thanks Intuit. I'll give those suggestions a try and report back. More likely its something other than the caliper slide mounts: I just cleaned and lubed those, and the inconsistent pedal happens when the brakes are cold or hot. But I will run the hot test you suggested. I'll also start paying attention to whether the symptoms have any relation to engine rpm.

 

[TTercel]

Did you ever resolve this issue? I seem to be running into the same issue after a track day.

 

[MauiRoads]

The condition is improved, but not resolved. I re-cleaned and carefully re-lubed the calipers and ran the tests Intuit suggested...and found no sticking calipers or pads. The condition had improved somewhat when I installed better, slotted rotors and Porterfield R4S pads. Much less touchy on initial bite, more linear feel, and they don't overheat on long downhill runs. I installed a new cruise control switch (see above) and it "seems" to have made an improvement. I now have a firm pedal most of the time, with less frequent and less severe softer pedal. I'll probably do another bleed with the full ForScan procedure, followed by a manual-pedal bleed. If that doesn't fully eliminate the problem, I'm learning to live with a quick "brake check" before hard braking.

 

[TTercel]

The condition is improved, but not resolved. I re-cleaned and carefully re-lubed the calipers and ran the tests Intuit suggested...and found no sticking calipers or pads. The condition had improved somewhat when I installed better, slotted rotors and Porterfield R4S pads. Much less touchy on initial bite, more linear feel, and they don't overheat on long downhill runs. I installed a new cruise control switch (see above) and it "seems" to have made an improvement. I now have a firm pedal most of the time, with less frequent and less severe softer pedal. I'll probably do another bleed with the full ForScan procedure, followed by a manual-pedal bleed. If that doesn't fully eliminate the problem, I'm learning to live with a quick "brake check" before hard braking.

Thanks for the update. I'm going to do a full brake and clutch bleed and see if that fixes it.

 

[kevinatfms]

Did you ever resolve this issue? I seem to be running into the same issue after a track day.

Im currently in the same boat. Had a terrible spongy pedal after two session of a track day earlier this year. Replaced the master cylinder and now ive gone through 8-10 bottles of fluid trying to get it to bleed the last few months. Just totally inconsistent and randomly spongy.

Used Forscan to ABS bleed it every way possible with a motive pressure bleeder hooked up with no resolve.

Its either a DOA master out of the box or there is somehow still air trapped in the ABS HCU block/lines. Going to bleed it again this weekend and cross my fingers it ends the crappy pedal feel.

 

[Dialcaliper]

Im currently in the same boat. Had a terrible spongy pedal after two session of a track day earlier this year. Replaced the master cylinder and now ive gone through 8-10 bottles of fluid trying to get it to bleed the last few months. Just totally inconsistent and randomly spongy.

Used Forscan to ABS bleed it every way possible with a motive pressure bleeder hooked up with no resolve.

Its either a DOA master out of the box or there is somehow still air trapped in the ABS HCU block/lines. Going to bleed it again this weekend and cross my fingers it ends the crappy pedal feel.

One Hail Mary suggestion if you haven’t done it already:

Try pulling the ABS fuse to completely disable the ABS system, and see if the problem goes away. It’s an outside possibility that it’s the ABS module itself slowly going bad, but not in a way that’s severe enough that the diagnostics can pick up on.

At the very least you might be able rule out a failing ABS module as the cause (like valves not closing properly). Have you noticed whether the spongy pedal happens after a stop that triggers the ABS?

 

[kevinatfms]

Spongy pedal all the time like it has air in the system. 1/2" of movement for the take up then pedal will slowly sink with barely any load on it.

Removed by big brake kit to see if it was the culprit and even with stock calipers, ABS bleed and regular bleed 3x its still spongy.

 

[Dialcaliper]

Spongy pedal all the time like it has air in the system. 1/2" of movement for the take up then pedal will slowly sink with barely any load on it.

Removed by big brake kit to see if it was the culprit and even with stock calipers, ABS bleed and regular bleed 3x its still spongy.

That sounds a lot like a stuck open ABS valve or one with a leaking seat. Air in the system would be spongy/squishy, but the pedal shouldn’t keep dropping

Reminds me of this somewhat older Ford Fusion recall. Different ABS unit type, but who knows?
https://www.torquenews.com/3769/for...es-keep-brakes-failing-due-sticking-valve/amp