WARNING FOR '91 and '92 EXs
If you have a '91 or '92 EX, please heed the following warning: The manuals all say that if any portion of the RABS fails, that normal (non-anti-lock) braking will still be available. That is not
ALWAYS the case. I almost rear-ended a little lady in stop-n-go traffic because my brakes failed. I think it was within an inch of a collision.
The pedal didn't hit the floor - it got reeeeal stiff but still NO more stopping power. This is a potential killer.
Anyways, frictions, drums, and rotors were all brand new so I really didn't know where to start. I tried to bleed the rear corners and couldn't get any flow, so I checked in front and after the RABS modulator and realized that it must either be clogged or stuck closed - didn't really matter as I had found the problem. Found a place (CarQuest) that had one reman unit in stock, and after swapping it in, I was able to bleed the brakes.
Now, what happened is that I stepped on the brake pedal, causing both the primary and secondary brake circuits to be pressurized. These circuits provide a force back through the pedal that is proportional to the amount of that pressure. The primary feeds the front brakes and the secondary feeds the rear brakes. There is NO proportioning valve or pressure differential valve on the '91 and '92 Explorer models, meaning the primary can't feed the rears and the secondary can't feed the fronts. If the RABS modulator valve is plugged or stuck closed, the fluid trying to go to the rear brakes has nowhere to go so it builds up pressure - and that goes right back to the pedal in the form of higher forces. The higher forces keep you from getting the pedal travel necessary to apply the front brakes (so they are at a really low relative pressure even when you are standing on the pedal). So what you end up with is a hard pedal in mid-stroke and no braking power.
Ford didn't really think thorugh ALL of the potential failure modes of this system and warn people of the risks - or maybe they did and didn't like the thought of Jay Leno doing a bit on them like - "Have you heard that the new Ford anti-lock brakes can malfuntion and severly reduce the stopping performance of the vehicle? I think they took the idea of not locking up the wheels a little far." Bah-dum-Dum.
The RABS modulator only cost $150 - the safety of myself and my passengers is worth way more. A cheaper way of solving this potential problem is to remove the RABS modulator and replace it with a section of brake line. The modulator has a small openings and would seem to get plugged easier than regular brake line. I might consider this option if this modulator plugs/fails. It is sitting pretty close to the left side of the exhaust Y-pipe....it probably gets pretty toasty.
