2002 F150 brake pedal fade
 

Last week my brake pedal started going to the floor when I stopped, it still stopped and felt fine on the top half of the pedal travel but then it would just slowly fade to the floor.

I took it to a local shop and they said the master cylinder was leaking internally and my rear brakes were shot. I have 75,000 miles and the rear brakes were original so I told them to fix it. This is basically what I expected it to be.

They kept thinking they were getting defective master cylinders but after the two Napa parts and two Carquest parts they realized they misdiagnosed it and said I needed to take it to the dealership. I paid for the rear brake job since it needed done anyways and have an appointment for next week at the dealership. Does anybody have any ideas of what might be causing the problem? I see no brake fluid leaks, no vacuum leaks, the booster was replaced 25,000 miles ago due to noise, no ABS light on, no CEL on, no other symptoms.

Thanks in advance! and Happy Independence Day!

loose bleader valve? air in the lines?

if it was a bleeder screw I think I would have a fluid leak, I was thinking that the first shop might have not gotten all the air out of the lines but they said they bled them repeatedly

Defective proportioning valve :confused:

isnt that in the master cylinder?

Look at the brake hoses for ballooning.

torkum & 93 mix n' match ~ I don't see a seperate proportioning valve, so I would assume it is in the master cylinder or the ABS block

Bluegrass 7 ~ I visually inspected the hoses and squeezed them between my fingers and didn't see or feel any weak spots, but thanks for the suggestion

Greetings, Have you solved your problem? I am having the exact same symptoms on my 02!

Since it feels safe to drive, and nobody seems to have a good idea about what to do next without throwing expensive parts at it, I am just driving it the way it is. I am hoping it will get worse so it will be easier to fix, but right now it is very consistent. If you figure anything out, PLEASE let me know!

hmm....how about this. get another person to pump your brakes with you listening under the hood. see if you can hear anything other then the normal brake pedal movement. you should hear the initial pump, then maybe the sound of air as the pedal fades.

I went out today and sucked as much fluid out of the reservoir that I could get. Then I refilled it with new DOT3 fluid. Now I will mention that the fluid that came out was factory fluid and REALLY dark in color. Since I could not locate any mechanical issues, I felt that perhaps the fluid had accumulated too much moisture. I Then started at the passenger rear wheel and bled it until the new fluid came out. I then refilled the reservoir and repeated with the other three wheels. I did notice a couple large bubbles in the drivers side rear wheel, but no air anywhere else. I also removed the master cylinder from the brake booster and turned the adjustable nut out a half turn.

I test drove the truck for about 40 minutes. After about 3 minutes the pedal faded to the floor. But that was the only time. I drove truck the rest of the afternoon and had no problems.

I will let you know if it returns.

I tried that, and didn't hear anything abnormal and didn't see any bulging in the rubber brake hoses with the pedal pushed,

gotta be the booster/master cylinder.

we tried a NAPA master cylinder and a Carquest master cylinder and neither one made any difference. I've never seen a booster make the pedal soft, when it fails the pedal is hard. But the booster is the cheapest thing to try so I might just try it.

Just to update you: I have put about 180-200 miles on my truck since I flushed the system and I have not had the pedal fade to the floor. So I went from having this happen every time I pressed the pedal, to working correctly.