I'm at my absolute wits end- Fading Brake pedal despite best efforts (2 Viewers)

[musthave]

First - Yes, I'm using the @NLXTACY line, but I'm truly at my wits end.

Beginning - Had fading brakes, bled numerous times, no air, no leaks. Replaced MC, still same issue.

Next - Bought NEW OEM MC, NEW Calipers, NEW Rotors, NEW pads.

Today - Bench bled the MC, installed. Installed new rotors, installed new calipers. Bled thoroughly no air, no leaks, still have the same fading brake pedal.

Facts:

1. System has been bled numerous times, after two MC replacements, still have fading pedal.
2. Bled system according to FSM, including LSPV valve.
3. Absolutely no leaks of fluid.
4. Absolutely no air in system when bleeding at calipers or LSPV.
5. Took brake booster out of the picture completely, had hard pedal, but fade remained the same, thereby eliminating the booster.
6. Visual inspection - When bleeding, no bulging lines, steady fluid at each caliper, so, no crushed lines. No sign of crushed lines elsewhere.

Noticeable items:
1. Fading - When bleeding the brakes, power off, we get a decent pedal, not perfect, but not fading.
2. Fading - With power on, we get a quickly fading pedal with almost no braking.
3. Fading - Once the pedal fades, the brakes are in a state where 1300rpm and I can move forward.
4. Fading - At a stop sign, the brake pedal to the floor, I will roll forward slightly, so no stopping.
5. After 3 quick pumps of the pedal, the capacity of the booster is reached, I get a hard pedal, but it fades quickly with little stopping effect.

The only two things that I can think now enter the equation:
1. The ABS unit on the left fender well, not sure how this comes into play, or how to diagnose, it is interesting to not as above that the fading pedal is absolutely most noticed with power on.
2. The computer that controls all of this stuff.


I'm almost $1K into this, really at my wits end, looking for help, suggestions, and...

 

[Roadhouse78]

Your lspv could be faulty. It might be sucking air into the system. My only other suggestion is replace the master again. If the seals are not working correctly fluid will pass by when pressed and cause pedal fade.

 

[jkilcullen]

air trapped in abs system is a possibility, I removed mine in the hunt to improve my braking, not sure if it was the culprit as I gutted abs, lspv and did new master at same time. Others have said to cycle abs on gravel roads in order to try to force air out of it, then follow it up with a rebleed. I know exactly how you feel, I was there earlier this year and it totally sucks.

 

[musthave]

Your lspv could be faulty. It might be sucking air into the system. My only other suggestion is replace the master again. If the seals are not working correctly fluid will pass by when pressed and cause pedal fade.

Question though, if air is coming in, wouldn't fluid HAVE to come out?

 

[jkilcullen]

others also told me it could be a booster but my thoughts are if the booster were bad it would have manual brakes and a rock hard pedal, someone feel free to give me a scenario how the mechanics of a booster could cause a different failure as I truly dont know how it could.

 

[jkilcullen]

Question though, if air is coming in, wouldn't fluid HAVE to come out?

not sure on lspv but I have had wheel cyls in drum brakes suck air and not leak.

 

[musthave]

air trapped in abs system is a possibility, I removed mine in the hunt to improve my braking, not sure if it was the culprit as I gutted abs, lspv and did new master at same time. Others have said to cycle abs on gravel roads in order to try to force air out of it, then follow it up with a rebleed. I know exactly how you feel, I was there earlier this year and it totally sucks.

Did you just disassemble the ABS unit on the fenderwell? Did you replace the LSPV, OEM?

 

[Landseer]

Did you try pulling the ABS fuse and see if theres any difference? Probably won't change anything but its easy enough to do.

 

[musthave]

others also told me it could be a booster but my thoughts are if the booster were bad it would have manual brakes and a rock hard pedal, someone feel free to give me a scenario how the mechanics of a booster could cause a different failure as I truly dont know how it could.

I agree, I don't think it's possible that it is the booster. After taking off the vacuum for it, I had a really hard pedal, but it faded the same with no stopping effect.

 

[musthave]

Did you try pulling the ABS fuse and see if theres any difference? Probably won't change anything but its easy enough to do.

Haven't tried that, but it's easy enough to try. That fuse is in the fenderell fusebox?

 

[Pin_Head]

Brake fade is the loss of braking efficiency during sustained braking due to heating of the brake pads and rotor.

What you are describing is a pedal that leaks down upon sustained pressure or a spongy pedal that pumps up but goes back the floor when you release it. The former is often due to the master leaking internally back into the reservoir. You can sometimes see turbulence in the reservior when the pedal is applied. The latter is may be due to air in the system or a balooning brake hose.

 

[NLXTACY]

First - Yes, I'm using the @NLXTACY line, but I'm truly at my wits end.

No worries, Wits' End will have a life of its own very soon

 

[scottryana]

Is "Wits' End" the name of your truck? lol

 

[1FZj80]

could be your abs module/thingy. I removed mine and it made a big improvement in pedal feel and braking performance.

 

[NLXTACY]

Is "Wits' End" the name of your truck? lol

Close, I'll give you a hint. I needed a new direction and distraction.

 

[musthave]

Brake fade is the loss of braking efficiency during sustained braking due to heating of the brake pads and rotor.

What you are describing is a pedal that leaks down upon sustained pressure or a spongy pedal that pumps up but goes back the floor when you release it. The former is often due to the master leaking internally back into the reservoir. You can sometimes see turbulence in the reservior when the pedal is applied. The latter is may be due to air in the system or a balooning brake hose.

That may be a better definition There is no turbulence in the reservoir. There is for certain no balooning brake hose.

Air in the system, I just don't know how/where it could be if that's what it is.

 

[musthave]

could be your abs module/thingy. I removed mine and it made a big improvement in pedal feel and braking performance.

Which one did you remove? Where?

 

[NLXTACY]

Which one did you remove? Where?

I think he means the main ABS control unit that is on the driver's side fender under the hood.

 

[musthave]

I removed the ABS fuse. Tried things out, appears to be the same as before, no change.

 

[izzyandsue]

Don't want to sound like captain obvious, but the ABS could be it.. That's why I recommend the Phoenix reverse brake flush when power or normal bleeding can't get all the air out. I have had similar problems in other cars, and the Phoneix took care of it. The way I understand it, there's valving in the abs system that won't allow flow unless abs is being activated. The flow direction is of course the direction you are bleeding. The reverse system pushes the fluid and air in a direction that the valves allow flow, therefore flushing out trapped bubbles. If you were near us, can borrow it, but Amazon can deliver in 2 days worse case.