Master cylinder going out?

[Darrman]

I replaced all my brakes on the '01 Sport a couple weekends ago, went all out. Here is what I replaced:
Rear pads with premium
Rear antirattle clips
Front rotors with new Motorcraft
Front pads with premium ceramics
Front antirattle clips
Front slide pin boots
Front bearings with new grease seal and dust caps
Everything was cleaned and reassembled with fresh caliper grease/wheel bearing grease.
Stopping power is tremendously improved!!
BUT.....
If I am riding the brake while doing low speeds, in other words parking lots, red lights, as I go to stop there will be good pedal pressure, then all of a sudden the pedal will start getting mushy and I can hear and feel the rotors grinding against the pads, like I lost pressure all of a sudden. It will continue to roll forward until I push real good on the pedal.
I have checked, double checked, triple checked, even taking the pads back out and looking at the wear patterns, all are good and even.
I have not bled the lines yet, but I did not open the lines either, so I dont understand how air could have gotten in. I did take a small amount from the resevior so I could push the pistons back in without overflow, but I know not to go to low and let it suck air. Plus I did not pump the brakes till after everything was done and the resevior was filled up again.
I am not getting a abs light, and I did clean the sensors.
So all this said, I am thinking its the M.C., I have a new one, but dont have a way to bleed the HCU.
Any thoughts or opinions?
Thanks!

 

[jlsparky7]

Check for leaks a WHOLE LOT. Bleed the brakes, recheck for leaks. If there are no leaks then its your MC going out.

 

[mritz]

Had this happen in my Expedition before
when moving slow and applying bakes it was like I had none and had to pump them to stop
actualy ended up being a bad sensor in the ABS never had a ABS light come on and only did it at slow speeds
had the sensor replaced and brakes worked perfect
dam scary when you push the pedal and have no brakes

 

[my98nnj]

You did all that brake work and never bleed (changed) the brake fluid, the blood of the system?

Brake fluid is hygroscopic by nature (absorbs moisture) and should be changed with every brake job. No changing it is the cause of most internal brake system failures.
Give the system a good bleed and see how it performs. If the problem still exists and your 100% certain the calipers, hoses, lines ect. and wheel bearings are in proper working order, then change the master cylinder.

 

[Darrman]

I know about moisture problems, I plan to change the fluid as soon as I can get some help. I will use a synthetic fluid, worked great in the clutch in the 92.
The thing is I have not altered the lines in any way, so how could I get air in the lines?
I never bleed a system till after I am sure that the new components are working proper, so it cuts down on figuring out what is wrong.

 

[swetrid]

Sounds like false abs activation to me, probably have a sensor dropping out. I have also sen people damage the tone ring area on 2wd rotors when they hammer the seal in.

 

[Darrman]

hmm, i cleaned the sensors and backing plates with simple green, they were coated in dust from the cheapo pads that were on it, hopefully i didnt screw them up.
I was careful not to hit the tone rings so hopefully thats not the issue.
Is there any way to test the abs sensors?

 

[Darrman]

Well it looks like it is the abs sensors, I ended up pulling the fuses out for the abs and the brakes work perfect just running conventional. So I am going to try cleaning them one more time and go from there.

 

[Paraphoe]

ABS = more trouble than it's worth?

Let us know if you have any luck cleaning or end up needing new sensors. I can't imagine that's cheap.

 

[Darrman]

I finally solved this problem last weekend, after replacing the sensors and getting nothing.
Turns out it was the tone rings, I bought a set of drilled and slotted rotors and that fixed it right up. Its weird, I dont see any damage to the old tone rings, but it may be to slight to see.