92 brake problem

[arquerogringo]

I had a soft brake pedal forever and the system was generally worn out so I replaced the:
pads shoes
resurfaced drums and rotors
hardware
calipers
wheel cylinders
master cylinder

The master cylinder was bench bled and the system was bled by bleeding the farthest wheel from the master cylinder first working to the closest.
I did this twice, the seconed in a troubleshooting effort. a couple of liters of brake fluid were used in all. There is no air.
The pedal is still soft. It brakes well but if I press with moderate force I can push it to the floor. There is no wall, and I want that wall.
Coould the booster be the problem, or could it be a bad new master cylinder?
Thanks,
Damon

 

[dogfriend]

Does the truck have ABS? If so, you may need a special tool to bleed the ABS system if it has air in it.

 

[arquerogringo]

It has RABS. my manual indicates that I only need to worry about the special tool and bleeding on the 4 wheel ABS in the '93 and after models. Is it right?
can I bleed that little porportioning valve on the chassis, and if so in which spot on the wheel to wheel sequence?
Thanks,
Damon

 

[dogfriend]

I think you can bleed the RABS valve. The sequence is to start at the point fartherest away from the master cylinder and work your way closer each time. So I would do the two rear wheels first, then the RABS valve, then the front wheels.

Does your manual have instructions for bleeding the RABS valve?

If it isn't the RABS valve, then you may have a leak somewhere in the system.

Edit: After looking here: http://www.autozone.com/servlet/UiB..._us/0900823d/80/0d/46/c0/0900823d800d46c0.jsp

It looks like there is not a way to bleed the RABS valve. I am confusing it with the Toyota PU that I own. I used to have a Ranger with RABS.

 

[arquerogringo]

so if I can positively rule out a leak in the system, and I know it is well bled, it would have to be the master cylinder, right? or is there something else it could be? If a booster goes bad you have a hard pedal, I was told, if so it cannot be the booster and I can't think of anything else.
Thanks,
Damon

 

[dogfriend]

In my experience, when you have a pedal that goes to the floor, it is usually the master cylinder that is the problem. I asked you earlier about ABS because its possible to have that problem with air in the 4 wheel ABS pump. If the booster is bad, you may have more pedal effort and travel, but it should not go to the floor.

 

[Brock94]

Another possibility is that the rubber hoses in the system are balooning when you push the pedal, in which case they should be replaced.

 

[arquerogringo]

I forgot to mention that I also replaced the front brake hoses, as one blew and that is the reason I started this complete brake system overhaul in the first place.

Is anyone familiar with the RABS control valve. Here is a picture
http://www.rockauto.com/ref/Raybest...ics.cgi?partno=ABS570030,style=P01,brand=5450

That nut that has a dust boot resembles a bleeder underr the boot. But it being on the bottom doesn't make sense. I don't want to ven try unless I know because I replaced it once long ago because on the old one it was leaking from that nipple.

I figure that it must be the new master cylinder must be defective if that valve is not involved. What a headache.

Thanks,
Damon

 

[bobbybob]

had this problem years ago. After replacing 3 master cyclinders and the control module my shop called in a Ford expert. Found out that the RABS control valve was sticking open sending all the fluid back to the MC. Replaced the valve and fixed the problem.