Really soft pedal hardly any brakes...

[atvkid4eva]

hey guys my buddy has a 93 explorer 4wd and the other day the brake pedal got really soft and went to the floor..could still stop but barely..so we thought it could be the master cylinder so we put a new one it bled the whole system completely and it is back to where it was with hardly any pedal..the truck has all new brake lines and leakes no fluid..good pads and shoes as well..what else could it be?

 

[kaytbugsdad]

If my memory serves me right, the RABS (Rear Anti-lock Brake System) valve and the proportioning valve are combined, and instead of pushing brake to the rear brakes, its bypassing fluid thru the valve back to the master cylinder....... Thats usually the reason you have a low brake pedal with no apparent fluid leak.......

 

[chazzone]

If my memory serves me right, the RABS (Rear Anti-lock Brake System) valve and the proportioning valve are combined, and instead of pushing brake to the rear brakes, its bypassing fluid thru the valve back to the master cylinder....... Thats usually the reason you have a low brake pedal with no apparent fluid leak.......

That doesn't sound right at all. The ABS control actually closes off each line if the sensor sends a signal that one wheel is locking up.

I don't see how this could cause a soft pedal.

There can really be only one reason, and that is a leak in the system, which could include a bad master cylinder.

Re-check and rebleed. If you're absolutely sure that the system is intact, it'd have to be the master cylinder.

There's got to be a leak in there somewhere.

 

[atvkid4eva]

there are absolutely no leaks...ive traced every brake line and they are all new lines...a new master cylinder was installed the other day and completely bled..there isnt any air in the system to the best of my abaility. what about the brake booster?

 

[Guilius]

I am dealing with a slightly similar problem with my Ranger after doing a rear Axle Swap to the explorer 8.8 (post is a few down from here).

i have gotten some information that if you have 4wheel ABS, it may have a Hydraulic Control Unit. If air gets into this, as it may have done with the master cylinder swap, your in some pretty hard luck. it can only be bled with a special tool from ford, and i have called around and the closest i found is 525 bucks. Dont as me what this tool looks like or how to use it, but they said they could do it in an hour and i refuse to bring it to a dealer.
im trying to get info on removing the HCU alltogether, and tying the three lines out from the HCU directly to the master cylinder.

this can explain the soft brakes even though it was fully bled. the unit has air in it.
mine are the same way and we adjusted the Pushrod from the master Cylinder, thinking that might be needed for the addition of the rear discs instead of the drums i usedto have, and they started locking up. readusted it back to normal and almost no brakes at all again.

 

[chazzone]

Here is what I found on bleeding the HCU. I've never had to do this before, but I found a lot of references to the issue.

http://www.justanswer.com/questions...lace-several-brake-lines-on-my-93-ford-taurus