So the other day for no apparent reason my brake pedal got really soft than within two or three stops it went to the floor and the ABS and E-brake lights came on. Parked the truck and looked all over for leaks, nothing.
Checked the fluid, good.
Now when the truck is off I have pedal, start the truck in park I have pedal, as soon as I put it in drive it starts to get soft. when I drive, if I jump on the brake my pedal is hard as a rock but I'm pretty sure its just the fronts, If I apply the brake gently or let off pressure after jumping on it the pedal goes to the floor.
*ABS and E-brake lights are solid , rears are supposedly ABS however I have my doubts they ever functioned properly.
Its worth mentioning one of my cylinders in the rear are sweating a bit but the pads are dry. When I disconnect the ABS fuse in the cab its worse. I have an ABS pump fuse under the hood even though I don't think I have an ABS pump, no power there. speedo works. E-brake also.
This is my only salt truck for this winter and I could really use some constructive input here, I'm totally lost for ideas at this point. I'd like to check the plug going to the solenoids so if anyone would have a diagram for that I would really appreciate it.

Thanks

 

Just a follow up...
took it out in some light snow this evening and after 17 years owning this truck I think I can honestly say this is the first time I heard, felt the rear wheels vibrate..lol lack of a better word.
If its the master how is it that I have pressure when the truck is in park or when I jump on the brakes.
I've been watching the fluid , hasn't moved.
I was reading a post here about how to de-activate the piston in the abs module. but if I have ABS my thinking is its not the solenoid, but than again if the dump solenoid is stuck and only pops in with a quick jolt of fluid ?? any thoughts? I could really use some pro advice before attempting the abs piston jam, even though it was posted on this site