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Discussion Starter #1
I havea 2000 F550 7.3 dually, and have been fighting brake probs for 3 yrs..I've stopped driving it now..Here is what i've done..all new rubber lines..4 new calipers and hardware..all new rotors.. what happens..if you stop easy...the pedal is at the top of travel..feels fairly normal..but if you have to stop fast,or with a load,the pedal when pushed hard goes to the floor with very little stopping power...there is no air in the system,and no ABS codes...all that is left is the master cly or the abs unit...if you push on petal with the engine off it is hard,with it on,and not moving it is very spongy....anyone have a solution?
 

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You may have a hydrobooster issue.

But ..... have you tried other F550's with hydroboost? The hydroboost system is not like a typical vac boost. With a vacuum system, the booster has a "runout" where no more assistance is given, then it's full mechanical between you, the pedal, and the master.

That's not true with a hydroboost and the easiest way for me to describe it as that your operating a valve the applies hydraulic pressure. Towards the last motion of pedal travel it's more like a rubber ball.

How good the friction material is can effect this as if the friction is not up to stopping the vehicle, then it's easy to get into the "rubber" mode trying to gt the friction material to do something. But a bad booster can also be an issue as I mentioned early on.
 

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Have u checked the power steering fluid level? Do you hear the pump when u push on the brakes really hard?
 

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Discussion Starter #4
You may have a hydrobooster issue.

But ..... have you tried other F550's with hydroboost? The hydroboost system is not like a typical vac boost. With a vacuum system, the booster has a "runout" where no more assistance is given, then it's full mechanical between you, the pedal, and the master.

That's not true with a hydroboost and the easiest way for me to describe it as that your operating a valve the applies hydraulic pressure. Towards the last motion of pedal travel it's more like a rubber ball.

How good the friction material is can effect this as if the friction is not up to stopping the vehicle, then it's easy to get into the "rubber" mode trying to gt the friction material to do something. But a bad booster can also be an issue as I mentioned early on.
We have 2 other F series diesels with hydoboost,,,none work like this one..all the friction surfaces arwe Ford brand,,,not low on ps fluid...this truck weighs 11000 lbs.,.and will not stop..
 

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Then if the power steering works fine it sounds like a hydrobooster is bad. Best I can do without being there.
 

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Discussion Starter #6
We solved about 75% of the problem today..We replaced the PS pump with a rebuilt one,and we seem to have more stopping power,still not as good as my other super duties,but way less dangerous to drive now,,,'I will post other info as I get it
 

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I have seen the hydroboost unit go out before and cause all sorts of issues as FMTRVT has stated. With the scope of your issues I would take a careful look (i.e. replace) at the unit.
 

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brakes locking up

I have 2000 f 250 new rotors pads and calipers in rear and new rotors and pads in the front. Drive the truck down the road and the brakes apply themselves locking all four wheels. I let the truck sit over night they released. Drive the truck again same problem. Called Ford and no recall. This seems to be a serious safety issue to have the brakes apply themselves. Anybody know what to fix . I also contacted National Highway Safety and let them know. If you are having this problem call the National Highway Safety @ 1 800 424 9393. If a enough people call with tis problem it could spark a recall. I feel this is a serious safety issue
 

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Two things come to mind. Did this problem exist before the new rotors and pads? If not then I would double check the installation. How easy did everything slide together. There is a remote possibility that things are too tight. If it took considerable effort to put the calipers back on there may not be any room for expansion and when things heat up and expand, they just lock up. The other thing that comes to mind would be the master cylinder. There are small bleed holes in the master cylinder that allow fluid to return to the resevoir. If for some reason the master cylinder is out of adjustment and the piston is blocking this hole or if there is dirt or corrosion plugging the hole, when the brake fluid heats up and expands it is unable to escape to the resevoir and just applies the brakes. Drive it with a wrench in hand and when the brakes apply crack the lines at the master cylinder to see if there is fluid pressure there. If that releases the brakes then the problem is master cylinder related. If there is no pressure at the master cylinder then crack the bleeder screws and see if there is pressure there. If there is no pressure at the M/C and there is pressure at the calipers then there is a blockage somewheere in between. I have long since learned that there are no absolutes when working on vehicles but I can think of no other possibilities. Good Luck
 

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After what I just went through, replacing the master cylinder solved all of my problems. I have 223,000 miles on my truck and, after driving it with a new master cylinder, I can now reflect back and see that it spent some time going out on me.

Like yours, mine were spongy for awhile, I replaced pads and rotors and bled the heck out of it. A week later I had no stopping power. At the suggestion of FMTRVT I replaced the master cylinder. Took a few minutes to do (an hour) and my truck has never stopped better.

If you change it, get a new master and not a rebuilt one. Mine from NAPA cost $109.00.

BTW. My truck is an 2002 7.3 F350 4 wheel drive single rear wheel.

Coolwhips
 

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I will say this, bleed them good before you do anything. Check for leaks. If that is all good then replace hydro boost and master cylinder since you will have it tore down. My pedal was going to the floor and there was no pressure feedback in the pedal, it was spongy with rubber ball feel at the end of pedal throw. I replaced both mentioned above, power steering pump and flushed brake and steering fluids and I am now good to go with a night and day difference with own style pads and rotors and did not pull a wheel to repair. Goodluck
 

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I had the same problem

I changed everything twice. Fail. It wound up being loose front wheel bearings causing the rotors to wobble and spread the callapers. 1 turn out or adjustment is all it takes. Pedal sinking is normal on 4 wheel disk systems.

99 E350
 

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My 1997 f250 does this. I have rear drum with rear abs. My mechanic said it is the crappy abs of my older truck. Pretty sketchy when the pedal drops on hard stop.
 

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Change master cylinder and hydroboost, that was my issue with same characteristics. I also have 4 wheel disc brakes. Problem solved 40 k miles later still working good on 2001 7.3L excursion with 212000 miles.
 

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2000 f-250 spongy break pedal!! help!!

I have bleed the break lines a millions of times. replaced the hydro boosted, power steering pump. still not working like they should... what should I do?
 
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