I got in my truck this morning and the brake pedal went to the floor. I had enough brakes to drive if I pumped, but even after pumping and holding the pedal would slowly bleed down. I assumed it was the master cylinder, so I picked one up, bench bled it properly, and installed. It's doing the same thing!
We got out first frost last night, but unless water was in there and it swelled a ruber line somewhere, I don't think it's relevent.
I can't see any leakage coming down the wheels from the wheel cylinders, and it's not loosing fluid.
Could it be a massive air bubble? How would one form all of the sudden?

 

Sounds like the RWAL dump valve is bad. Hippie got tired of replacing his and had a shop machine a connector to eliminate it entirely.

 

Thanks Dave.
It definately feels like it is the rear barkes that are having the problem.
I hate to be ignorant, but what and where is the RWAL Dump valve?

 

When mine done that, it was the master cylinder.

 

OK, I looked it up, but still don't know where it is, unless it's right under the master cylinder. I hate this kind of crap!

 

The RWAL dump valve is mounted on the driver's side frame rail near the axle.

 

Is the dump valve the same as an ABS Brake modulator? I'm trying to find one online...

 

Should be. Dodge calls it the "hydraulic control valve".

 

I can't find one by any name online. Where do I get one?

 

Is this it?

 

Mine hasn't failed yet so I haven't taken a good look at it, but as far as I can tell from the drawing in the FSM it sure looks like it.

I was gonna suggest the Dodge dealer, where did you find that?

 

Right here...
http://www.partsamerica.com/ProductD...e=1395&ptset=A

 

Thanks! Now I know not to pester the parts guy at Dodge when mine goes out.

 

Sooo, can I be relatively sure enough that this is my problem to shell out $100 smackers? My wife dished out some silent approach over the bad call on the master cylinder!

 

If there are no visible leaks and you have a new master cylinder, this is the only thing that could cause a sinking pedal.

The old master cylinder didn't owe you anything. Besides, the brake fluid needed changing anyway.