I feel like I have gone full-circle with brake performance on my 2000 F-350.

It started with what I considered to be deteriorating brake performance, exemplified by a "soft" or "long" pedal, and reduced modulation.

This was diagnosed as a bad master cylinder. It was replaced, along with rotors, pads, calipers and a number of brake lines, one of which was leaking due to corrosion.

After all this work, when I picked up the truck and drove it a little, I still thought the pedal was soft and the brakes just not working as well as I think they should.

Pedal symptoms as follows: upon start-up, without moving, if you put steady pressure on the pedal, it will slowly go all the way down to the point where it can't go any further. If you drive and come to a stop and sit there and keep steady pressure on the pedal it will do the same thing. The brakes work, the truck will stop, but there is very little modulation, it seems the brakes are either on or off, and the pedal feels "soft".

I went right back to the dealer and asked about this. They seemed to think it was somewhat normal for the pedal to fall under the above circumstances, but the service writer tried the pedal and allowed as how he thought it was a little greater than it should be.

They took the truck in and worked on it, saying that they re-bled everything twice and thought they did get some air out, and upon road testing said the situation was better.

Itook the truck out and it did seem much better. Under both of the above pressure situation, the pedal did not go all the way to the floor. It hit and seemed to hold a firm bottom, and you could put your other foot under the pedal, between it and the floor. Also the brakes seemed to modulate much better, responding to increasing pedal pressure with proportionate braking force. HOORAY!

NOT SO FAST - The next day, the "soft" symptoms were right back again, and that's where we are now, and I am getting really tired of this situation.

What is going on here? Is it possible that the master cylinder they used as a replacement is defective as well? ( Seems very unlikely, but it could be )
Or, is there some other component in the system, that hasn't been replaced yet, that could be causing this condition. ( Don't know what else there is - power boost; proportioning valve; ABS component(s)??

I have more time and money in this fiasco than I care to think about, and I want to go back to the dealer and tell them to fix it right once and for all, but I feel I need some additional knowledge on my side.

I had previously asked a question about the replacement of the leaking brake line running inside the frame rail from front to back, and you guys were very helpful and correct that the gas tank did not have to be removed to do this, and I thank you all for your input.

Can you save my bacon again, and help me figure out what is going on?

Thanks.

 

Had your truck been pre `96 I would have said right away that you had a defective Rear Anti-lock Brake System valve. However I don`t know if your later truck just has RABS or full four wheel ABS.

 

I just bought a 95 F350 dually for my Dad and it has a similar problem. The guy I bought it from said Ford said it was the master cylinder and he replaced it (with one that has a switch on the end not being used). Then they said it was the rear adjusters and he had to keep manually adjusting them. Now I read this and wonder what the real problem is.

Mine is a little different problem, I get a jerking in the vehicle when I put the brakes on. If I press harder then a feather, they will throw you through the window. Just a little pressure and it will stop but then the pedal will keep going. You talk about a defective RABS valve. How do I check it?

 

First off the "jerking" you mention is probably warped front rotors. Second I am not sure if the big F350 had RABS. When you first switch the ign. to "on" does a ABS light momentarily on the dash? If so then you have RABS. If not crawl under the truck at about the drivers door hinges and look on the inside of the frame rail. You should see the brake pipe running from the firewall down to the frame rail. Does the pipe go into a steel block with wiring connections to it before running on down the frame to the rear axle? If so then you do have RABS. The sinking pedal could also be caused by air in the system. However it is not that big a job to eleminate the RABS as the problem. Do the above checks and post back.

 

im havin the same prob in my 94 f150. ill have to look into it...
ill let ya know.

 

I'm not an expert on the RABS but I think you got a bad master cylinder. Make the dealer fix it and don't give them another dime.

 

Well I did some checking and this is where I am at now. I do have RABS. I took the truck to a shop for a free inspection. They said the right rear was over adjusted and the rear drums needed turned (the right took three passes). The rotors were out of tolerance and would need to be replaced (this requires the new ones mounted to the hub on the truck and then turned in place). They said the master cylinder was the wrong one. I told them I thought the system just need to be bled. They showed me how they isolate the mater cylinder (they crimp the flexible lines at all the wheels to isolate) and the pedal still went most of the way down. They said that means it was the wrong one or bad. They gave me an estimate for $748.00. I have never taken my vehicle to a shop for brakes. I about fell on the floor. Talked to my Dad (who really owns the truck) and he said do it.

Now a few hours later (3.5) I go back to the shop. When I drive up in my Chevy (with tinted windows) the truck was parked out front and two mechanics bent over looking at the front right tire. They glanced at me but could not see who was driving. When I parked and got out, they stood up real quick (like they had just been caught). I asked what they were looking at. Mechanic two said he was checking the front pads because they still smelled (it smelled to me like burnt clutch-the truck is Auto). He said the pads have not seated in yet and that was the problem. Then Mechanic one (the guy who did the work) told me they did not like the pedal travel and thinks I need a proportioning valve. I asked to see. My son opened the hood. First thing I noticed was the brake fluid on the fire wall, fender and engine. Mechanic one pointed out this gold piece on the side of the master cylinder (the rear brake line was attached to it) and said that was the proportioning valve. I asked them about the one on the frame. They both insisted that there was not one. I looked from the top and could see something (now think it is the RABS Valve). Mechanic one started to get frustrated (OH WELL) and walked off. Mechanic two tried to tell me there wasn’t one. I then asked if they check the ABS valve. Oh that is in the rear end. I had to explain that the sensor was in the rear but the brake hose has to go through something to control the fluid to the rear. He said I should drive the truck to see what I thought of the pedal travel. After driving it around the block and the pedal moving the same as it did before, I took it back. Mechanic two met me when I got back and asked what I thought. I said it is the same. And to me that means the master cylinder was not bad. He then said he would like to bleed it again because the proportioning valve is sometimes hard to get the air out of. I said go a head. It was 4:45 by now and I had not slept yet (I work the midnight to 0800 shift) and had to be back to work this night. I told them I would be back tomorrow. Will have to see what I get when I go back today. I will keep you posted.

 

I have seen a few rwal valves go bad and feel like a bad master cyl (pedal sinks) there are 2 valves and an accumulator in the valve. When the rwal computer sees the rear wheel speed neering lockup, it activates the 1st valve to not let any more fluid to the rear wheels. If they still try to lock up it opens the other valve to relase pressure into the accumulator. If this second valve leaks (which they do sometimes) you get a dropping pedal as the fluid fills the accumulator. To tell I have gotten under the truck (not running for noise purposes) with a stethascope while someone puts steady pressure on the brake pedal. You can hear the spring in the accumulator compressing. I have bypassed the valve before to fix cheaply (they didnt work that well anyway)