Brake Issues

['94IDITurbo7.3]

I have been having some break issues lately. i read in my ford chilton manual that if the vaccum pump is bad then it will send a code and turn on my break waring lights. is this true or will the pump slowly go bad?
When my truck is idleing i can pump the breaks up and get the pedal up near the top. then just the weight of my foot on it will make it sink to the floor. i have no fluid leaks.
I have blead all of the old fluid out of the system. the old fluid looked like it had some water in it. When i slam on the breaks in my driveway the pedal goes to the floor & only my front breaks lock up. my rears don't even think of locking up. i just replaced my VSS in the back. it appears that my rears are either not getting power at all or not getting full power.

Could a bad vaccum pump cause these symptoms or does this sound like it is an issue w/ the rear brakes?
I have no break warning lights on.

Any help is appreciated

 

[franklin2]

A bad vacuum pump will give you a very hard pedal. It sounds like your problem may be a bad master cylinder which is leaking internally.

 

['94IDITurbo7.3]

i just put in a master cylinder rebuild kit.

 

[7.3 powerstrok]

did you bleed the master before you installed it ?

 

['94IDITurbo7.3]

yes i did bleed the master. then i hooked up the brake lines to the master, then i had my dad pump the pedal. i went from right rear, left rear, front right, front left. i have also blead the ABS valve inside the driverside framerail. i have done this proccedure 3 times and same result.

 

[Smokey73]

another thing to consider is the RABS valve. It has been known to leak internally. The only way to test it is to bypass it, or block it off and see if the peadal still fades. I had a similar problem and I bypassed the valve to see if the problem went away, when it did, I left it bypassed.

 

['94IDITurbo7.3]

How do i bypass my ABS valve?

Would the ABS valve leaking internaly give the same type of symptoms as a leaking line would b/c that is what this reminds me of, but i know for sure that i have no leaking lines?

 

[Smokey73]

Read this article. Although it is for a Ford Bronco it applies to our trucks as well.

http://www.asashop.org/autoinc/dec99/techtips.htm

I think this is the article I got my info

 

['94IDITurbo7.3]

Thanks for the article, it was very informative. this will be my next step.

 

[7.3 powerstrok]

check 1...air in system? check 2.....fluid leaking ? check 3 rear brake adjustment & calipers ..if all good then its most likely the master cyl

 

['94IDITurbo7.3]

Check the rear brake adjustment. If they're adjusted I'd think about checking the RABS valve. A good way to check it is to unscrew the big hex cap on it and take the spring out, put the cap back on, then take it on a test drive. Your rear brakes should have major stopping power, locking up easily. If none of that works, it could be the master cylinder.

By taking out the spring and then having the rear wheels lock up that would point to a bad RABS valve, correct?

 

['94IDITurbo7.3]

When i open the RABS valve and take the spring out do i need to then bleed my rear brakes & the RABS valve?

 

[Compu Doc]

Don't take any springs out of it. Replace it if it is bad. Being that you rebuilt the master cylinder go through the steps in the article as it could still be the master cylinder causing a problem and not the RABS valve. The RABS valve looks like the one pictured here. It is along the frame on the drivers side.

You must be registered for see images

 

['94IDITurbo7.3]

The master cylinder is pretty simple. if i just rebuilt it what could be still bad in it?

 

[7.3 powerstrok]

bleed the lines at the master cyl ? test the master cyl plug the line outlets if the pedal sinks then you know for sure!!!