Replaced pads and rotors, brake pedal sinking to floor now?!?

[UniqueTII]

I just installed a Powerstop Z36 on my 2015 XL and I cannot get the brake pedal to stop sinking to the floor. I didn't crack the system at all, just retracted the pistons with channel locks (bleeders closed) and replaced everything as normal. As soon as I went to test the truck out, the pedal was mushy and would creep toward the floor. I bled about 2 gallons of fluid through it, including while cycling the ABS pump with a Snap-On scanner. Nothing has helped at all.

I assumed it was the master cylinder, so I removed that to look for leaks and found nothing. After that I reinstalled it and bled it, then capped off the ports to test it. The pedal stayed firm even with the truck running, so I don't think that's the issue. They're on back-order everywhere, but I did find a used one on eBay that was already on the way.

The next step was to disassemble everything to make sure the caliper pistons moved freely, the sliders were okay (I cleaned up the rears a bit), and to open the bleeders while retracting the pistons this time. No help. After that, I pinched the lines with vice grips and narrowed the issue down to the front. With both front lines clamped, the pedal firms up pretty well. If I remove either of the vice grips, it sinks again (even if pumped a couple of times). We did another bleed on the fronts tonight using a standard 2 person method and that didn't help.

I didn't see any flex in the brake lines, but I have a new set on the way anyway. What the heck else can I do?

 

[07navi]

I just installed a Powerstop Z36 on my 2015 XL and I cannot get the brake pedal to stop sinking to the floor. I didn't crack the system at all, just retracted the pistons with channel locks (bleeders closed) and replaced everything as normal. As soon as I went to test the truck out, the pedal was mushy and would creep toward the floor. I bled about 2 gallons of fluid through it, including while cycling the ABS pump with a Snap-On scanner. Nothing has helped at all.

I assumed it was the master cylinder, so I removed that to look for leaks and found nothing. After that I reinstalled it and bled it, then capped off the ports to test it. The pedal stayed firm even with the truck running, so I don't think that's the issue. They're on back-order everywhere, but I did find a used one on eBay that was already on the way.

The next step was to disassemble everything to make sure the caliper pistons moved freely, the sliders were okay (I cleaned up the rears a bit), and to open the bleeders while retracting the pistons this time. No help. After that, I pinched the lines with vice grips and narrowed the issue down to the front. With both front lines clamped, the pedal firms up pretty well. If I remove either of the vice grips, it sinks again (even if pumped a couple of times). We did another bleed on the fronts tonight using a standard 2 person method and that didn't help.

I didn't see any flex in the brake lines, but I have a new set on the way anyway. What the heck else can I do?

The lines seem to be a weak point on these trucks, get back to us after you install those ones you have coming.........

 

[Plati]

That happened a few years ago on my 2003. Pedal would just creep all the way to the floor. I just drove it slowly around the block once. All good. Don't understand it but brakes are fine.

 

[UniqueTII]

We did take it out for a drive after the first part of the process and nothing improved, unfortunately.

 

[JasonH]

Pedal should firm up after several presses. If it doesn't, check for sufficient fluid in the reservoir and leaks in the brake line bleeder screws.

 

[UniqueTII]

Pedal should firm up after several presses. If it doesn't, check for sufficient fluid in the reservoir and leaks in the brake line bleeder screws.

Reservoir is full and haven't found any leaks, but thanks for the feedback!

 

[07navi]

Pedal should firm up after several presses. If it doesn't, check for sufficient fluid in the reservoir and leaks in the brake line bleeder screws.

He hasn't put all the parts in yet.

 

[Retiredusps]

Had and old ford pickup same thing master cyl was bad leaking internally. by passing. it was common years ago with single system.

 

[Bobmc]

Had and old ford pickup same thing master cyl was bad leaking internally. by passing. it was common years ago with single system.

I had to replace my 2010 EB master cylinder a few months ago for this reason. Brakes worked normally with light pressure, but pedal went to the floor if I pressed more than moderately hard.

 

[UniqueTII]

Had and old ford pickup same thing master cyl was bad leaking internally. by passing. it was common years ago with single system.

I did check the master cylinder by plugging it and the pedal firmed up when I did that.

 

[Yupster Dog]

My brother-in-law had the little to no brake and couldn't figure it out. I went over and took 1 look and saw the bleeder screws at the bottom of the caliper. we reversed the drivers side and the passengers side got the bleeder screws on top and all was well.

Funny thing is he knows better and just didn't see it. Sometimes it is the obvious and you just don't see it.

 

[Trainmaster]

Change the brake hoses.

 

[UniqueTII]

Change the brake hoses.

Just got them today so I'll report back tonight!

 

[UniqueTII]

We changed the hoses and calipers tonight and did another bleed (ABS system first, then another manual bleed) and nothing changed with the pedal pressure.

 

[outdare]

We changed the hoses and calipers tonight and did another bleed (ABS system first, then another manual bleed) and nothing changed with the pedal pressure.

My 07 the mechanic need a scan tool for the ABS to activate the valves. Can you get the ABS to activate while driving? This may cycle the pump. I found this it is a E350 but may pertain to this issue.


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[UniqueTII]

My 07 the mechanic need a scan tool for the ABS to activate the valves. Can you get the ABS to activate while driving? This may cycle the pump. I found this it is a E350 but may pertain to this issue.


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The Snap-On scanner will activate the valves for each wheel, which is what we used. I'm thinking the Hydraulic Control Unit is having issues so I have a low mile used one on the way. The only thing left is the booster but I don't know how that would cause this symptom.

 

[iamthedavem]

I have to agree with retiredusps on the idea that the master cylinder is leaking internally. There is no other place in the system that a leak could occur that could cause the pedal to go down without leaking outside of the system. Fluid under pressure causes the pistons at the wheels to move but the o-rings in the master cylinder cannot keep the fluid from seeping back past them and returning to the reservoir. Usually, in a two reservoir system this doesn't happen because one system doesn't allow the fluid to return, but one system would still leak back taking the pressure off the affected brakes while the other one maintained it's pressure. Once the second system fails, it then behaves like a single reservoir system allowing the pedal to sink to the floor because of the internal leak.

 

[Dustin Gebhardt]

Where are you clamping the front lines at?

Based on what I've read, it sounds like you have a problem at the caliper(s). I say this because you state that the pedal feels good when you clamp the front lines. At that point, you've virtually eliminated all of the other components as possible sources of the issue. The master cylinder holds pressure. The rear brakes hold pressure. The ABS holds pressure. At that point, all you have left is the front lines and calipers.

 

[GaryH2]

I would suspect the lines (which you have ordered). I had issues with mine where they would bleed ok and looked fine, but must have collapsed internally. New front lines fixed it up right.

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[UniqueTII]

Thanks for the new responses! I do have a spare (used) master cylinder I can throw on there, but I didn't suspect the MC because it held pressure when plugged. I did see someone test one with only one port plugged, though, so maybe I should try that.

I replaced the front lines and calipers, followed by a full bleed including the ABS system, and nothing changed. I just swapped out the ABS HCM but haven't been able to do a full bleed yet, so we'll see if that helps.