I own a 97 Ford f150 XLT 6 cyliender 4.2 automatic 4x4 and after i replced the Fornt pads and the rear shoes no matter what, the pedal goes to the floor when i start the engine. With the engine off the pedal is hard.
I decided to repalced anything and everithing regarding to the brake system to no avail.
Replaced the master cylinder twice,,replace booster twice,,replaced front loaded calipers and rear shoes and pistons..replaced all brake lines,,replaced the ABS valve.Bleeded the master cylinder,,the ABS valve and all the wheels left rear right rear,left front and right front several times until no bubbles appeared and double checked the hardware instalation and adjusted the rear shoes properly. I even lenghtened the rod on the booster. With the engine off the pedal is hard but as soon i start it the pedal goes to the floor.
I hear that the ABS valve need to be bleed by a scanner so i removed it and bypassed it but still the pedal goes to the floor.
I belive i replaced about everything that is replaceble on the brake system and now im flabbergast and not knowing what to do.
I will appreciate any help i can get.

Thanks.

Temy

 

Sounds like a Vacuum issue, most brake boosters have a vacuum line going to it I would check that out.

 

The vacumm at the booster is fine

 

it sounds like normal. ive owned a couple of fords and every one when you do a brake job and get ready to pull her out ya gotta pump the brakes to pressurize em again. not to mention countless other vehicles ive worked on. it should have to go to the floor when you first start it and have to pump it some to bring em back.

 

Well....As of now i dont haver any brake at all. I have pumped it with the engine off and on hundred of times and dont get presurissed. The pedal always go to the floor.
Me and a mechanic worked on it for a couple of days and still the pedal go to the floor.
Mechanic conclusion? it's possessed. LOL

 

lol. yeah then i'd agree ya got a pretty good problem on your hands if they still wont pressurize.

 

When you changed the vacuum booster, was there a new check valve installed in it, or did you use the original on that was in the old booster?

 

I changed it twice and both time with new check valve

 

It is also important to bench bleed the master cylinder, but I'm sure you did that. The only other thing I could suggest is the the push rod isn't properly seated at the brake pedal.
What method are you using to bleed the wheel cylinders?

It sounds like you've covered everything else

 

I really don't know what else to do. Yes i did bench bledded the master cylinder and checked the rod for proper alignment several times. I bleeded the wheels cylinders with vacum and also manual numerous times.

 

I had a similar problem when I replaced the master cylinder on my 97. It finally worked out with a lot of pump hold and bleed. I never did quite figure out what was causing my problem.(other than air) But I kept bleeding, the manual way, with a two man team. It just seemed to take a reticules amount of bleeding.
I recommend you put all the lines back to original factory connections and keep bleeding. I didn't have much luck with vacuum bleeding.


Remember, Pump up, hold, second man open the bleed valve, until the pedal goes to the floor, then he closes the valve, and repeat. Start with the farthest wheel from the master cylinder.

I'm sure you know this, but just thought I would repeat it.

 

Im having the same problem with my 95, ive replaced the master cyl, the booster, replaced the wheel cyls,adjusted the rear brakes, changed the proportioning valve it already had new calipers from a month back. I have bleed the system a dozen times and it keeps doing exactly what you described. It pumps up rock hard when the truck is off and when you start it it falls to the floor. Ive had it! It is driving me crazy! If you figure anything out keep me posted and ill do the same. sorry for hijacking your thread

 

I'm at a total loss ... when you find put what the problem is (and I'm sure you will) post back and let us know

 

have you tried gravity bleeding the system?

 

Well heres my update, I had to use the truck for a short trip to move something. While i was driving in i hit the brakes and they went to the floor and then i heard a loud bang and felt it in the brake pedal. It was as if something was jammed or stuck and had broken free. I released the pedal and pushed it again and the brakes were back! The pedal is firm and the truck stops fine. I dont know what happened but im happy to have brakes again lol. I hope this helps the op with his problem.