I have tired reading every thread and trying everything with no avail.
I have a 1997 F150 XLT 5.4L 4X4 EXT Cab. Front disk, rear drum, 2Wheel ABS.

Front:
NEW Rotors
NEW Calipers
NEW Pads

Rear:
NEW Shoes
NEW Wheel Cylinders
NEW Spring kit
Turned Drums

I replaced all of that beacuse it was getting about time to replace it and i had a very very soft pedal and even when I really got on it i felt like i didnt have very much brake. ABS would not even kick in.

After replacing it all basically nothing was better except the squeek from the rear drums was gone. When applying brake with truck not running its pretty solid but if you press really hard it will sink about half way. With truck running the pedal is super soft and can press it nearly to the floor without tons of effort. Went on driving it to work because i had to.

About a week later brakes failed completely, pedal went to the floor and i had nothing.
Put on a NEW Master Cylender. Bleed the system starting with furthest to the closest. Did this several times before we were getting any good pedal pressure. Then took several more bleedings to get all the air out.
But once done nice hard pedal. Only sink about an inch if you really push on it. Then started the truck and the pedal is back soft and squishy. Turn off the engine, pump the brakes a couple times and its back hard again.
I have checked llines, no leaks, and hoses arent bulging anywhere.

So I started researching things. Read about possible air in the ABS system so I went in my field and slammed on the brakes a few times. Didnt feel like ABS was really kciking in. So I went down my street and slammed on the brakes. Came to a stop somewhat quick but didnt feel ABS and no skreeching tires.
So I started tightening the rear brakes. Tightened them till they were pretty hard to turn the wheel by hard. Then went back out and tried the same thing.
This time stopped quicker and i did skreech tires i think I felt ABS some.
Did it a few more times. Came in and bled all 4 wheels. I did get a little air from the passenger rear wheel. But none of the others.
So I thought maybe that was it. Started the truck... nope soft pedal by pushing hard it will go at least 3/4 to floor maybe more.

Read this post about the shaft between pedal and booster.
http://www.f150forum.com/f6/spongy-b...esolved-77511/
I turned it out 20 turns. Nothing different. Went 10 more. Things could be different but I couldnt swear to it. Started the truck same thing.

Read this post about the power booster shaft adjustment.
https://www.f150online.com/forums/wh...ment-pics.html
Took allot of measurements with micrometer. I'll get into that later. But for the sake of trying i turned it out 1/2 turn counter clockwise.
Started the truck nothing different.
About the measurements. Here is a picture trying to show what i found.

The way this looks the power booster shaft longer than the recess in the MC piston. So it is actually depressing the MC piston slightly even when there is no pressure on the pedal. I dont know where this should be just stating what i found.

So now I am out of ideas. PLEASE PLEASE PLEASE anyone ANYTHING

 

wow, where to start?

The reason the pedal feels hard when the engine is off is that you deplete the vacuum in the booster. Without vacuum boost the pedal feels harder.
Once you start the truck you pull vacuum and your boost returns, hence making the pedal feel softer.

It sounds like you have done a thorough job of bleeding. Have you tried changing your flex lines? Perhaps they are starting to fail and "swell" under the pressure. This would make your pedal feel soft.

Adjusting the pedal position will not affect your pedal feel... it will just make the pedal closer to your foot to begin with. IF you adjust it too far you may get into a situation where the pedal self-applies and you have dragging brakes.

As to the booster output rod adjustment - generally the rod will be longer than the recess in the primary piston on the master cylinder. This is done to make sure you always have contact and to properly locate the primary piston. It is difficult to know for sure what the booster output rod measurement is supposed to be... perhaps you could check with the service department at your local ford dealer.


What kind of pads did you install? More aggressive pads will make the pedal "feel" harder.

But the next thing I would do, if I were you, is to replace the rubber lines and then rebleed again.

 

I think i will go today and get new flex lines.
i will update on how this helps.

thanks for your input. thought the same thing myself about the pedal possition adjustment. I failed to see how it was doing anything except moving the pedal closer. And after 30 turns its probably only 1/8" closer.

 

Replaced the lines and bled the with power bleeder pump on all 4 brakes. Had allot of trouble getting them bled. But when I got it done I still have the same problems. The brakes are no better.

 

I have lengthened the pushrod on the power booster until when i replace the MC I can feel it touching. THis really seemed to help the brakes. They were a thousand times better. I was afraid they would be too tight or rub so i jacked the truck up and all four wheels would spin and didnt fee like there was any brake drag.
I drove it to work for a week. Then pulled my boat about 75miles to the lake. On the way a guy slammed on his breaks to try to turn into a yardsale. I locked up the breaks and they really did good. Stoped the truck and boat in the same amount of time as if the boat wasn't there. The boat trailer has surge brakes by the way.
I Drove around while I was there. Then towed it back home.
The next day on the way to work i was on the interstate running about 55-60mph. The truck slowly started slowing down to about 50mph like i was on a hill. I pressed on the accelerator a little more and the truck down shifted and acted like i was towing the boat. Then the truck started vibrating really hard and spoke started coming from the passenger side wheel well. I pulled the truck over into the median and the passenger side from brake was dragging, very hard. To the point i had to give it agressive throttle to move it. I cracked open the bleeder valve. let the fluid come out until it got to a drip. Then shut it back off. Then started the truck and everything seemed to be fine. I drove it back home about 25mph just to be safe and took my other truck to work.
What could cause the caliper to lock up without ever touching the brake. And why did everything work so well until now?

 

I have owned three 97 F150s all 4wd with different trim packages...but all had a squishy feeling pedal that would go almost to the floor...i thought maybe it was normal??