Brake trouble

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Oct 2, 2005 | 08:34 AM

roymacrews

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Brake trouble

1993 Ford F350 Crew Cab, 4x4, 4 wheel long bed, w /7.3 pre-power stroke diesel and manual trans. When driving recently, between one brake application and the next, the pedal went from solid to soft. Braking force was still good, no fluid was lost, but under steady pressure the pedal would go to the floor. Every part in the system except steel lines has been replaced. Front Calipers, rear brakes, ABS module, booster, master cylinder, flexible lines, even the vacuum pump are all new. It is exactly like it was after whatever broke, broke. It still stops fairly well, still doesn't leak fluid, but the pedal will go to the floor under steady pressure.
I and my mechanic are stumped. Any ideas?

Oct 2, 2005 | 08:51 AM

Kwikkordead

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From: Rio Rico, AZ.

Quote:

Originally Posted by roymacrews

Welcome to the forum. Man, I feel your pain.
I moved this thread to the appropriate forum.
A slow fade like that is IMO always a hydraulic leak. If you are not losing any fluid then I would say that you have a defective master cylinder, bleeding down between the chambers. You've replaced everything else, including the flex lines, so they are not swelling.
When you say ABS module, you talking about that little unit that's mounted under the driver's seat in the frame rail?

Oct 2, 2005 | 02:51 PM

roymacrews

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Brake Trouble

You would surely think master cylinder, but we have tried two NAPA master cylinders and then two new Ford Master Cylinders w/o any effect. In 1993 ABS only worked on the rear and the unit is in the frame about under the driver's seat. We've bled a gallon of fluid through all four wheels and it is still just like it was. I've been messing with the thing for about two months now. You're right about the PAIN.

Oct 2, 2005 | 05:12 PM

Kwikkordead

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From: Rio Rico, AZ.

Hmmm, well about the only thing left is that sorry excuse for an ABS unit. I have no knowledge of how it functions other than the theory of design. If it were my truck I would unplug the electrical plug from it and drive it to see what happens. The light will most likely come on in the dash, but for the experiment, not a big deal.

Oct 27, 2005 | 05:42 PM

twister08

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I am having the same problem. we are on our 2nd master cylinder from Napa.

We bypassed the ABS Valve under the cab completely, and still having problems.

we have a hard pedal (diesel engine shut off), and try bleeding, but are getting tons and tons of air in the rear. Non stop, air.

Start the truck up, the pedal goes right to the floor.

How did you make out??

Oct 27, 2005 | 08:00 PM

roymacrews

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After my long time and trusted local mecahanic gave up, I tried a Ford dealer. They bled, adjusted, charged me big bucks, and declared it fixed, but the pedal is still soft. I have had the truck since it was new. The pedal was always solid. All at once it went soft, and it is still pretty soft. so I don't believe it is supposed to be like it is dispite the protestations of the dealer. Unlike your situation, my brakes work pretty well, and when we bleed the system, I'm not getting air. Some one told me to try an F450 master cylinder and it would fix the problem. I haven't tried it yet, but I intend to. I'll post the results. Good luck.

Oct 27, 2005 | 08:12 PM

twister08

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I did read an article about the master cylinder may not supply the volume that the dual pistons need in the front... (that being the original replacement).(bore size)

This doesn't pertain to me, but for you maybe. IF someone is saying to use one from a f450, maybe that might be for you.

Ford issued a TSB on 1995 F250 and F350 Light Trucks.
bulletin # 98-5A-34 and the issuing date is 3/18/98.
It is titled "High Brake Pedal Travel or Low Brake Pedal Feel".

I found this informatin in here somewhere under someone having brake problems.
There were 3 links posted by someone, in PDF format.

It has a FORD part number chart for master cylinder, by application.

Good Luck