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Brake pedal slowly goes to floor! 2001 F-250 Superduty, 7.3, 4wd. My wife complained about the brakes one day. The truck stopped fine, but the pedal continues to floor each time you stop. No fluid leaks! Master cylinder is/was full. brakes were not worn out but due for replacement. Did brake job, same problem, replaced MC, same problem.

Any Ideas? Thanks!
 

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i have a 2000 f 250 4x4 crewcab. it does the same thing! slam on the breaks goes to the floor. cant even get it to skid. thought it was just how these trucks drive but my dad recently got a excursion 7.3 and u slam on them in tht and the thing stops sooo much better than mine. i would also like to know what is wrong. not derailing your thread or anything
 

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Usually pedal to the floor is a bad master cylinder. The fluid is bypassing internally in the master cylinder and it won't leak. What happens, even with new/reman ones, is the cups get flipped inside out. This happens because of time on shelf etc. When you bench bleed a cylinder you should only push the piston in about 1/2-3/4 otherwise you risk problems until the fluid gets moving and lubricating everything inside.
 

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brakes

It probably is leaking (internally) master cylinder, but let me tell my story on 2001 F250XLT. at 220,000 miles, left house one day did the same thing pretty much went t ofloor nadwhile it stopped, had very little brake. I thought the same thing, Master Cylinder leaking, but no leaks. thought maybe interanl and it would go into the power steering hydro-boost system, but No. So after I was doing yardwork for several hrs, I noticed my chrome exhaust tip was kinda wet looking, looked up under rear of truck, and the hard steel brake line running from Tee on axle housing to pass rear caliper, had a flatspot/tiny hole rubbed in it. Turned out at normal driving it doesnt hit my MBRP 4" exhaust, but when towing my 40' ATC G.N racecar trailer and with the back sitting down some ,the 4" exh was rubbing the brakeline for sometime now.

Maybe you will be as lucky as just a simple leaking line.
 

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mine was SOMEWHAT remedied by adjusting my rear drums. but mine had barely any pressure and would go to the floor, but if you pumped them they got hard. now i have plenty of pedal, but it still goes down if you press hard enough. not all the way to the floor, but id say a good 3/4 of the way. try that first as its a free fix and just good maintenance anyway. you just want a little drag on the drum. if you dont know how, pm me and i will give you a detailed description. and if you do, well i hope i didnt insult your intelligence.
 

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our trucks have disks in the rear. as far as the brake pedal at idle i can push it to the floor with ease but if i turn the wheel any ill get some more pressure but not much at all. is there a way to test the master cylinder? i know its not leaking externally because i have not lost any fluid
 

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Discussion Starter #7
yeah, 4 wheel discs. The power steering pump had always whined, from day one and the fluid was off-color and dark. I replaced the pump and flushed the old fluid as well as I could by myself, and bled brakes again. New power steering pump had a slight growl to it. Flushed ps pump with help, according to manufacturers recommendations, again. Tried to trick the ABS module by doing the hard braking on gravel road. and re-bled brakes again, first with gravity, and then by pumping the pedal and bleeding. NO CHANGE in the fading pedal problem, but now I have a groan coming from the ps unit when I step on the brake pedal and/or turn the steering wheel. PS pump is full of fluid.

Looks like I added another problem!
 

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is there a way to check for the leaking master internally? what about a pressure or something to check? also how much do the masters run for? can you rebuild them?
 

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is there anyway to test it?
 

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Not anyway that I know of, except for the pedal feel. No testing method i am aware of.
 

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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.
 

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Sinking pedal is not normal with any brake system, but loose wheel bearings as you noted can cause a long pedal, but not sinking pedal. Once the caliper pistons extend all the way there is no reason for the pedal to keep moving.

There are two checks for a master. Plugging the outlet ports if you can find the proper plugs at NAPA and see if the pedal will drop is one, but if the cup sealing issue is deeper in the bore that will not tell the story. A fast hit on the pedal that holds pressure while a slow apply drops the pedal is a better standard, but again not perfect.

Some people who have bought consumer auto parts store M/C have had bad units out of the box. The Motorcraft parts seem to have a better track record.

Another possibility is the ABS unit (both RABS and 4 wheel) bypassing internally. There is a procedure to check the 4WABS in the service manual and noted in my facebook page.

http://sphotos-a.xx.fbcdn.net/hphotos-snc7/293370_150321205049237_4815910_n.jpg

For a RABS unit, you can either bypass the unit by playing with the hard lines or loosening the lock nut on the unit and backing off the adjusting nut, but be very sure of noting how many turns you have turned it.
 

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Thank you Jack for your reply! This will help to cure me from my Parts Changing Addiction. I have searched the internet forums and come up empty for an answer. You hit it out of the park with that one! Please start a Thread on the subject and make it a Sticky. There are lots of people out there with the same problem. Your link is not on your Facebook page. I did find your Emergency Brake info there very helpfull. Do you have more info hidden somewhere? I now own 2 Master cylinders, 2 Vacuum Boosters, 2 ABS systems, and 2 Vacuum Pumps. It cost me $80 to have a break mechanic tighten my wheel bearings which got the 99 E350 to stop.
 

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brakes

It probably is leaking (internally) master cylinder, but let me tell my story on 2001 F250XLT. at 220,000 miles, left house one day did the same thing pretty much went t ofloor nadwhile it stopped, had very little brake. I thought the same thing, Master Cylinder leaking, but no leaks. thought maybe interanl and it would go into the power steering hydro-boost system, but No. So after I was doing yardwork for several hrs, I noticed my chrome exhaust tip was kinda wet looking, looked up under rear of truck, and the hard steel brake line running from Tee on axle housing to pass rear caliper, had a flatspot/tiny hole rubbed in it. Turned out at normal driving it doesnt hit my MBRP 4" exhaust, but when towing my 40' ATC G.N racecar trailer and with the back sitting down some ,the 4" exh was rubbing the brakeline for sometime now.

Maybe you will be as lucky as just a simple leaking line.
If it Was leaking into power steering then which part is bad? The MC Or the Boost?
 
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