98 F-150 brakes problem

[78 Chevyrado]

Its not a chevy, but i need to get this fixed ASAP.  its my dad's truck.

I've totally redone his entire brake system, everything but the hardlines, Rear ABS valve and booster have been replaced with new stuff.

I've gotten it all done, except the pedal is low and feels spongy.  ive bled it like crazy, and the only place i think any air could be is inside the RABS (Rear ABS ONLY) valve.  i cannot find any info in this RABS valve that says anything special in the bleeding procedure, and theres almost nothing about the valve itself.  I want to see if any of you pro mechanics have come across this problem and would share the answer with me.  as far as i can tell through research, the valve exists, but there aparrently nothing inside it (sarcasm) 

so is this RABS valve a pita to bleed or something?  I havent taken it apart, because if I screw it up a new one costs $250.  any tips from you guys or should i take it to a ford dealer and have them bleed it.  I know for a fact that if you get air inside the 4 wheel ABS valve, ford has to bleed it, or i have to buy the ABS code reader to hold the valves all open for bleeding.  however i havent found anything yet about the rear wheel only RABS valve. 

any help will be greatly appreciated.  links and pics are great.  even the ford factory manuals dont tell me about the valve, only how to replace it.  unhook the brake lines and elec. conn. then hook them up to the new unit.  thats all i can find.  i cant find one or id find a junkyard unit and disassemble it to see whats inside. 

this is holding me up big time.  hes using my car while i fix this and i need my car, cus the truck needed work the last few days and though i have 2 cars, i had to go borrow one and i hate doing that.

thanks guys!  I appreciate it greatly!

might be a Ford, but its a cool one! 

[VileZambonie]

Did you bench bleed the master? Did you try creating a false ABS stop? Check for brake fluid being supplied to the Rear Antilock Brake System (RABS) valve as the brake is applied. If present, check for brake fluid out of the valve. If none, you need to replace the RABS valve.

[VileZambonie]

Here's some pix

[78 Chevyrado]

Did you bench bleed the master? Did you try creating a false ABS stop? Check for brake fluid being supplied to the Rear Antilock Brake System (RABS) valve as the brake is applied. If present, check for brake fluid out of the valve. If none, you need to replace the RABS valve.

I bench bled it properly (at least like i always did, on the bench till no bubbles whatsoever were present).

whats a false ABS stop?

havent checked the supply to the RABS valve.

Theres at least some fluid out of the valve to the rear brakes.  they seem to apply like before (as in, even and adjusted properly)  just the pedal is low and a tad spongy when holding the pedal like at a stop.  after a little bit ( 5 or 6 seconds) of holding the pedal, it sinks a little more, but consistently each time.

[VileZambonie]

Get the rear wheels off the ground and put it in gear. Accelerate and hit the brakes, it should cause an active abs stop or go play in the loose sand/stone. Another option is find someone with a scanner that can open the valve for bleeding.