Okay, here we go... I posted this back in April and I thought I had the problem fixed, but NO. I have a 94.5 F-350 dually, 4x4 with the early powerstroke engine. It all started when I changed the master cylinder about two years ago. I could never get a brake pedal after that and I went back and forth with the parts store thinking I had bad masters. I bench bled all of them and even took it to a garage to have it bled on a machine to ensure no air was anywhere. After that I just went insane replacing every brake component on the truck. Thus far I have replaced the vacuum booster, (twice, just in case I had a bad one) the vacuum pump, the calipers, rotors, drums, shoes, pads, wheel cylinders, proportioning valve, all new hardware and adjusters and even put a motorcraft master on it for good measure. I went through the business of adjusting the rod coming out of the booster and still got no pedal. Now, it is worse to the point of being dangerous. I used to be able to pump the brake and get a pedal but now when I pump the brake I either get no pedal at all, -a very sick feeling in the pit of your stomach when you have a load on- or the pedal will get so hard I can't push it at all. I am thinking vacuum pump again since it was one of the first things I replaced nearly two years ago but I sure don't want to start all over again. Any ideas?Thanks for any thoughts! Norma

 

I remember reading about the clutch/brake pedal bracket breaking or the pivots wearing through on the early trucks. Mostly for the clutch though.
Take a look under the dash to see if your getting full travel on the brake pedal/rod.

 

Thanks Jim, I will take a look at that. Wouldn't it be awesome if that is the problem?

 

wonder if it could be a vacuum leak not letting the booster build enough vacuum??? I'm at a loss on this one. wonder if the zero loss booster and F-super duty master would help any

 

RABS maybe?

 

Are the rear brakes adjusted properly?...

 

Thanks Rick, yes the brakes are new and tightly adjusted. In fact I had them really tightened up to compensate for not having any brakes. If I pump the brakes I sometimes get a pedal and the brakes will lock up in the back, otherwise I get no pedal and it is very hard to push like when you have no vacuum. I do get a very loud whoosh sound when I depress the pedal. I cannot remember if I always heard that or not. There is one component that I did not change and I hope one of you can help me identify it. It is a little block on the inside fender that has lines going to the vacuum pump and the vacuum booster, it has other lines that probably go to the heater and a couple of capped off ports. Could this little devil be causing any trouble? Thanks to everyone for all your suggestions. Norma

 

It may be an issue with the vac pump again. The block is (IIRC) a manifold. (again IIRC)There is a check valve in the line going to the booster ,its the plug itself. May be an issue with that also.

Does the pedal fade more than normal?

 

Hi Rick, the pedal definitely fades more than it used to. It goes straight to the floor the first time I push it every time. The second time I push it, it might get hard or give me some pedal. If I really pump it it just gets hard and I cannot stop the truck at all. How would I know about the IIRC? What could I check on that? Thanks so much, Norma

 

IIRC is if I recall correctly , sorry. If you have to pump the pedal that much I would think the M cyl isn't working . May be a combination of m Cyl & Vac pump ..

When you were adjusting the rod in the M cyl, did you get it back to its original lenght?..

If it is not adjusted properly, the fluid ports can be partially Or completely blocked . Also, Do you have access to a vac test gauge?

 

x2 maybe try to bypass the RABS to rule it out

 

The whoosh noise is most likely vacuum. The inside ac/heater system is going to defrost mode because the system is loosing vacuum, and it makes that sound. I would suggest checking out the manifold you described above and all hoses connected. Here is a picture of it on my rig ...

 

Thanks Jim, mine looks somewhat like yours. What do you mean by defrost mode? I know that someone mentioned checking my heat\defrost control. What would I look for? The blower is putting out just fine but that has nothing to do with vacuum does it? Thanks, Norma

 

The vent doors on the ac/heater system are controlled by the vacuum system, if you are hearing a wooshing sound when you are depressing the brake pedal, that woosh may be the vent door actuator loosing vacuum.

 

Turn on the heater to vent or floor, press the brake , if the heater defaults to defrost momentarily , it is a vac problem...