From that excellent link that aerocolorado supplied us, comes the following: "Diagnosing these problems depends on which type of EH valve the vehicle is equipped with. The valve shown in Figures 5 through 8 is what I call the "torpedo"-style EH valve. It is cylindrical in shape. The most effective way to check this valve is to remove the 1-1/4" cap screw at the end of the valve body. Next, remove the accumulator spring. Insert a screwdriver or other suitable tool so that it rests against the accumulator piston (See Figure 9 above). Have an assistant start the vehicle and apply the brake pedal. Care must be taken not to apply the brake pedal too hard, or you won’t be able to prevent the piston from moving too far. If the piston moves, the dump valve is not sealing and the EH valve needs to be replaced."

Has anybody tried this? I looked at the valve on my '95 4WD Aerostar, and there are two 3/4" cap screws, one on each end of the valve. One of the cap screws has a little button in it and is farther forward. The other has no button on it. I didn't see a bleed hole on either one. Any idea which should be removed?

I'm diagnosing a somewhat soft (compared to my Ranger) brake pedal and a light went off when I read about the leaky valve being a cause. I've vacuum bled/flushed the system, running about two of those big bottles of brake fluid through and no change. I'm still able to lock up the front wheels on dry pavement but the pedal just doesn't feel like I think it should. Maybe it's in my head?

By the way, I've checked the hoses with pressure on them and they're not blowing up like balloons so I've ruled out bad hoses as the cause. I don't think it's the master cylinder because the brake pedal stays steady for a given applied load. But, if I press hard enough, the pedal will go to the floor.

 

Mikeman, I had a spare RABS valve in the garage, so I pulled it out to check some things for you. On the '91 the assembly is a monolithic block capped with the two solenoids and a single 'cap screw/button' feature as you described. For what's its worth, the 'button' is a rubber cap covering the plunger vent hole. (To allow for air displacement, in the event the plunger moves in the bore from hydraulic pressure on the opposite side.) The vent hole is 7/64" in diameter and runs the entire length to the base of the plunger. The plunger resembles a spent shell casing with the empty end out. There is a large plunger retaining spring carried inside the casing, which extends all the way up to the inner side of the cap screw. It looks like you could test your plunger theory by removing the rubber cap and inserting at least a 4" piece of coat hanger sized wire until the plunger is contacted. This way no disassembly would be required. I would guess the second cap screw on your RABS is for servicing/assembly purposes of the isolation valve.

I too have never been able to get a really firm pedal, even after replacing all the brake components. The feel is softer than I would like but still nicely progressive in feel and response. It has never gone to the floor. I would check that dump valve for sure if yours goes down that far. Something's amiss there.

Hope this helps.

 

Thanks for the info. I was looking at the wrong valve. I later found the ABS valve. Silly me, I expected it to be easily visible.

It turns out that I work with a guy who used to design ABS systems for Chrysler and is of course familiar with those used by Ford and Chevy. They all used pretty much the same or very similar hardware. Anyway, he gave me a bunch of information to look over. He says that Ford brakes are known to be softer (over boosted) compared to those of other makes and thinks that if performance is OK and troubleshooting doesn't turn up anything, then it's probably just the nature of the beast. I have spoken to other Ford owners who have noticed the same thing that I am with my Aerostar. I'm not too concerned yet because I can generate enough brake pressure to lock up the front wheels, but I'll still be checking things over as time permits.

 

Put this in the FWIW category, but I have found that despite being self-adjusting, the rear shoes are chronically out of adjustment. Just a small amount of adjustment makes a big difference in pedal feel.

 

A good suggestion. Thanks. I should have remembered to check the adjusters after having owned a '71 Maverick with drum brakes at all four corners.

 

Here's an update. I adjusted the rear brakes as aerocolorado suggested. This improved the pedal feel. Both rear brakes were quite a bit out of adjustment. The pedal gets stiffer sooner now, but I can still push the pedal to the floor if I push hard enough. Now the pedal feel is about the same as my Ranger so I won't go looking for problems.

 

This pedal to the floor is interesting. Mine won't go more than 1/3 down then stops solid. Been contemplating this for a few minutes. I know you checked the front hoses for bulges and can rule those out. The only two other posibilities I can even dream up are:

Aleakage around one of the caliper seals into the rubber dust boot. Of course eventually this would blow the boot off but in the meantime?????

BI read somewhere (not about Aerostars in particular) about fluid loss out the back MC seal that would travel along the push rod into the boost assist and pool there. This guy was constantly topping off his reservoir and could never find a leak anywhere.

 

Thanks. Those are good suggestions. But, other than for the periodic brake system flush (about every two years), I have never had to add any fluid to the MC reservoir. I just did the brakes and the calipers looked healthy.

So, when you say the pedal is solid after the first 1/3 travel, is this with the engine on or off? I have been referring to brake operation with the engine on so vacuum is available to power the booster.

 

With the engine on. There is just a slight softening if I really keep the pressure on, but still doesn't go to the floor. (PS, I don't know why those smiley faces are showing up in the previous post, I didn't put them there.)