I have a 1990 F-350 with 7.3 engine and 5 speed trans. The brakes fade to the floor . I have put on 3 master cyls. and two sets of calipers . Bled the sys. of air every way imaginable . but nothing has fixed it. The pedal when first applied is at the top , firm not spungey . The truck is loaded quite heavy but stops very well . I blocked the outlets to the master cyl . to see if it was bypassing and it stays firm as a rock and stays at the top . I also can plug the lines at the caliper end of the hoes on both sides and the pedal stays firm and at the top. But when i connect the calipers and bleed the system they will fade to the floor. I also found that if i press the pedal with the engine off that the pedal won't fade . Other than the pedal fading the brakes work great .My concern is that on a long enough hill with a heavy load that the brakes will not hold enough to get stopped befor fadeing to the floor . Has anyone got any ideas on what the problem is ? This is the first time iv'e ever failed to get a brake sys. working properly. Any help will greatly be appreciated .By the way . I was told that the preportioning valve could be the trouble but it don't have one on it . I also blocked the rear brakes off and it stiil does it . Some of you guys are pretty sharp and probably know what's wrong . But after 35 years of experiance this one has me stumped . sorry for the long post but it's hard to help without all the details . This is my first time to post on this site so please be patiant . I don't know if i will get an e-mail or find a reply on the site someplace . Thanks Rick

 

Any replies will be under your post, just like mine.



Welcome to the site!

 

Does that model engine have a vacuum pump like the Powerstrokes? If so, that's one place I'd suspect trouble.

 

mine does the same thing . i too have tried plugging the ports at the m/c and it stays firm.replaced the m/c- no help; replaced the calipers- no help; replaced all the rubber brake hoses- no help; replaced the RABS valve- no help; replaced the vacuum pump- no help. i am stumped. every time i try something else and it doesnt help i do this. i have bled the lines and the m/c repeatedly, both manually and with a mity-vac vacuum pump. still no help. i too have never had so much trouble trying to make a brake system work. it is very frustrating. i am thinking that maybe the steel line that runs along the backside of the engine crossmember is not bleeding properly, as it has too many bends/high points in it. i hope to find a shop with a machine that can pressure bleed the system. if that doesnt help, i am going to try replacing the line along the engine crossmember with one that runs more level and see if that helps. if anyone can tell me what the problem is and it helps me correct the problem, i will ship you a case of your favorite drink.( no b.s. , i will) i am that desperate. thanks, - marty

 

I am the first to admit i am not a brake guru ...
does the length of the plunger into the master cylinder have anything to do with the problem you are having? I changed a stock master cylinder to oversize one and noticed the plunger was adjustable and there is some type of guage available to check the proper length. just my 2 cents

 

i forgot to mention that mine is a '96 f-350 4x4. i guess i need to type up a signature. i think i'll do that now.

bilder12, i looked at that and it seems to be alright, but i guess i'll check it out a little more closely. thanks for the reply. just keep 'em coming guys. surely there has to be something simple that i have overlooked. btw, the offer above still stands.

thanks for such a helpful website, -marty

 

Thanks so much for the replies . To marty: Sorry your having the same trouble .But at least now i know i'm not loosing my mind . I made a bleeder a few years ago so i could bleed brakes without help. Its a simple hoes to go on the bleeder with a check valve that i made on my lathe on the other end of the hoes that lets the fluid bleed back into a container . If this is air it's the first time iv'e ever seen the peddale full and firm the first strock . Not saying that it's not air but iv'e siphon bled , pump bled ,and pressure bled them and i am not getting any air when i bleed . I also retrackted the pistons in the calipers with the bleeders open then started over hoping to force any air out . Still didn't help . But i'm thinking on the same line as you that air in one of the piston bores would give the fluid somplace to go . It's sure going somplace when they fade .
bilder: I checkeed the master cyl. today and it has the same travel as my freind has on his truck the same year as mine .I also double checked the free travel on the rod while i was at it and it's ok too.
Quadzilla I don't know what the power stroke has on them . However i have put two pumps on this one and it didn't help.I have very good brakes except that they fade when you hold them for a reasonably long time .
Any way Thanks to all of you for the replies keep them comming . I'm open to try anything at this point . Thank God i can do my own work or i'd be bankrupt by now . The garage that i do use occasionaly don't want anthing to do with this problem . He said he already had one about a year ago and had to refund the mans money and take a loss on the job ,cause they never did get it fixed . I guse these kind of problems helps to keep me humble !! Now that i'm humble i'm ready to get the thing fixed . Thanks fellas . Hope to hear more frrom ya . Rick

 

fading brake. I have the same problem on a 94. The only thing that makes sense after replacing master is that the abs block has gone bad and is bypassing fluid back to the to the master. look if you have 4 lines to your master, 2 out flow and 2 return. I was told that the abs block has springs that may get hot and lose their tension? fluid has to go somewhere, it either is leaking or bypassing. My abs light does not come on, and a code reader did not pick up a failure.

 

Hey guys; I guess I'll join in and say my 95 F250 has the same brake problem and it is a pain in the a--. When I'm not towing I can live with it, but the heavy loads are tough. I'm not ready to start installing parts because I see from the posts than the cure hasn't been found.

stroker393
Tony in NC

 

Thanks for thr replies on the fadeing brake problem . I have done a lot of resurch and experments on the problem and have come up with an explanation : Here goes : I was told that when you aply trhe brakes on a vehical with a vacume pump that is run via the engine that it just keeps aplying more and more vacume to the sys. causing a sinking pedal . Also i have found that after i put a new vacuum pump on that the problem is worse than it was with the old one . So i went to work and made a relief valve ( Check Valve ) that i put inline just ahead of the booster . When i adjust the valve to prvent full vacuum the fadeing brake pedal is greatly (improved but not elimanated ) . So back to the drawing board . I was also told that this is normal behavier for this type system . Evan though my truck will lock up all wheels and stop a fairly heavy load I personaly don't call a fadeing brake pedal normal !! One prerson put a differant style booster on and stopped the fadeing pedal (BUT HIS BRAKE ARE NOT AS GOOD AS THEY NEED TO BE !!!) So i think that all he did was used a booster that produced less pressure . See what you guys think of this idea i have come up with . I think that there is so much extra fluid in the large cavity calipers that it allows the fluid to be compressed . So when i get time i am going to take my old calipers and see if i can redesign them so they hold less fluid . Leaving less fluid to be compressed . I don't know if this will help or not but (I AN'T DRIVING AROUND WITH A PEDDAL THAT FADES !!!!) i'D LOVE TO PUT ONE OF THESE TECH PEAPLE IN THE PASANGER SEAT WITH ME DOING 70 mph PULLING A HEAVY LOAD DOWN HILL AND LET SOME IDIOT PULL OUT IN FRONT OF ME . THEN AFTER BARELY GETTING STOPPED IN TIME TO SAVE OUR *** !!! SEE IF HE STILL DESCRIBED IT AS NORMAL )It's a cope out from the manufaturer just like in 1972 when some of them stopped refering to badly running car as poor running and rediscribed it with the term drivabilaty) Any way after we have spent our money on these vehicals with problems .They got their money and if we want it fixed we have to fugure out what the MFG. did wrong and fix it ourself . I just feel soo bad for the peaple that can't do there own work and have to pay some poor mechanic to try to fix a design error . Stay after it fellas we'll eventualy figure it out !! Thanks to all that have responded . I'll keep you posted with anything new that i find .

 

Sounds like your brakes can't handle the load of stopping heavy loads. I don't have a truck yet, but am looking, but know a little about brakes. You might try semi-metallic brakes. Normal brakes work less the hotter they work, look at semi's going down hills. Semi-metallic brakes work better as they get hot, and if you get the right ones, you can't get them hot enough. Check at www.tirerack.com for brakes. Hope this helps

 

You guys, My father in-law had the same problem on his 95 F250, We found out that they made a bigger diameter master-cylinder for these trucks. The piston diameter is 1-1/4. It did the trick!!! It doesn't stop on a dime, but it stops 100% better.
Rich

 

how about the recalls and the tsb's in this forum??
there are some recalls in the brake systems, but cant tell if its for your problems. this is only a penny's worth ...