I'm having an odd problem with my truck that is driving me up the wall. I have an '03 club cab 4.7L Dakota, with four wheel discs (rear ABS.) A couple days ago, after about a 50 mile highway trip, the brake pedal was very soft when I got off the highway. The next day I looked at it, and it isn't leaking (the master cylinder is still full) and I did a visual inspection of all four calipers and see no leakage. The flex hoses look to be in good shape.

Since everything looked OK, I took it out for a drive. The pedal felt fine for most of it, but intermittently would go almost to the floor and then firm back up. I've had brake systems get soft in the past, but never come back afterward.

Any one have a clue what my problem might be?
Thanks!
-Bill

 

start out by bleeding your brakes...COULD be a bad master, but try the bleeding first, could have a tiny bit of air somwhere...

 

Hm. Further info...

I went out to check and see if the booster was holding vacuum or not, which of course required R&R of the vacuum line and the check valve.

Now that it's back together, it seems to be fine. Pedal is nice and firm and high again, but only when it's moving. At a stop releasing and pushing on the pedal again gives me the spongy feel.

I didn't get to bleed thebrakes yet - I still plan to. I am however very confused by the symptoms...

 

is it holding vacuum i assume? from what your last post said now it soulds likea vac leak...