F-150 brakes

I just replaced the front brake pads, rotors, calipers, caliper frames and master cylinder on my 1997 F-150 4x4. With the engine off, I get enough pedal pressure to bleed the system, but absolutely no pedal pressure with the engine running. Any ideas? At this point, I can’t even drive to a mechanic.

But did you bench bleed the master cylinder ?

Did you bleed the RABS (Rear Anti-lock Brake System) valve below the master cylinder?


I did bench-bleed the new master cylinder but did not bleed the RABS. I have a Haynes manual for my truck and didn’t see a mention of that. However, I bled all 4 wheels until all air and the old fluid was purged. Even with some residual air in the system, shouldn’t I get SOME brake action? Would not bleeding the RABS cause the brake pedal to go straight to the floor every time?

The RABS valve has a bleeder on it. If the RABS valve has air in it, there will be no hydraulic pressure to the rear brakes so the brake pedal sinks to the floor. Bleed the RABS valve the same way you would bleed a wheel cylinder.


Thanks, guys. Not sure I’m out of the woods yet. Other discussions on this topic outline big differences between ABS and RABS. My truck has a rather small modulator under the master cylinder, with one line leading to the rear of the truck, so I’ll assume I have RABS. But, I can’t find a bleeder valve. Any help?

Spent all morning looking for a bleeder valve somewhere in that system. No luck. I’m at the end of my ability to address this unless someone out there has another suggestion.


[i]In case anyone else ever bleeds their brakes and what not, they should know as well. I think it messed me up a bit also.
Its right under the firewall about 3 inches in front of it in the frame rail on the drivers side.

The Bleeder is 5/16’s
Mine was not reefed on there very tight, which I suggest others just snugging it back up nicely when they are done as well.
This thing would not be fun to “screw up”[/i]