Persistent excessive brake pedal travel problem.

[Dborch41]

2014 Nissan Frontier SV with almost 90K miles. I've never been a fan of the softer than usual brake pedal on this truck and I understand it's a known issue. Well it seems to have gotten worse, with enough pressure I can make it hit the floor. The fluid was flushed over a year earlier and no air ever entered the system. A new master cylinder didn't help, a "known good" used ABS module also didn't make any difference. No leaks and the pads and rotors are all good. I locked up the brakes on some gravel to activate the ABS and immediately bled over a quart through the system using speed bleeders, the pedal seems to stay off the floor now but there's still more travel than I like.
Here's the weird part. With the engine off and the booster bled down, the pedal is rock-hard and doesn't sink or feel spongy at all. As soon as I start the engine it goes soft again, I can't imagine it being the booster as that's not how they work.
Does anyone have any input? There's never been a brake or ABS light and I'm fresh out of ideas. Thanks in advance.

 

[Oil Changer]

Replace the rubber hoses.

 

[Dborch41]

Replace the rubber hoses.

I probably should have mentioned that, already installed braided steel lines...no joy.

 

[michaelluscher]

Is there an ABS bleed function on a scan tool?
Because just cycling them and bleeding again might not be enough

Are their any load sensing/proportioning/bias valves throughout the system?

 

[Dborch41]

Is there an ABS bleed function on a scan tool?
Because just cycling them and bleeding again might not be enough

Are their any load sensing/proportioning/bias valves throughout the system?

The service

Is there an ABS bleed function on a scan tool?
Because just cycling them and bleeding again might not be enough

Are their any load sensing/proportioning/bias valves throughout the system?

Surprisingly the service manual doesn't require the use of a scanner to cycle the ABS solenoids while bleeding the brakes, just to disconnect the ABS electrical connector or negative battery cable and bleed normally in a particular order. There are no other components in the system, the lines go directly to each wheel from the ABS module.

 

[Joba27n]

If you have drums, adjust your drums. I've found pedal feel is largely dictated by drums. Otherwise, measure your disk runout. A disk with alot of run-out may not cause a pulsation but it will push the pads back a little further than they should be which will lead to you having to press the pedal further and in turn "take up that space" before the pads make contact again. Last two things I can think of at the moment is either your pad material has some give to it or your brake booster is "over boosting". Try taking a short isolated drive with the booster deactivated via vacuum line being capped off and see how it feels

 

[Joba27n]

Also forgot to say, when ever you remove drums or rotors, you should be cleaning the rust off of both surfaces until they are shiny and bare. Rust will throw off the runout, as will a loose wheel bearing

 

[mrbreezeet1]

Are the slider pins all nice and free. Bound up slide pins can cause a low pedal, don't seem like it would, but it can.

 

[Dborch41]

Are the slider pins all nice and free. Bound up slide pins can cause a low pedal, don't seem like it would, but it can.

Yep, the calipers all move freely and pad wear is even. I cleaned and lubed them thoroughly during the last brake job.