I have been fighting this brake system on this 92 e350 all this week.I replaced calipers ,2 master cylinder,new booster ,bled the thing 10 times.No matter what I did the brake pedal would sink to the floor.I have read alot of posts on here with guys having this same mystery problem.Well I went to ask the brake guy that has solved every brake problem I have ever had.He told me in 30 seconds what the fix is.He has seen this problem quite a few times on local fleet trucks.It seems the front calipers flex and the stock
1-1/16 bore master cylinder ,that is the same size as a half ton master cylinder by the way,doesnt move enough fluid per stroke to completely engage the brakes when they get this age.
The fix is get an 89-90 F450 superduty master cylinder.It is 1-5/16 bore.It is almost a direct bolt on.The only modification is you have to slot the mounting holes toward the center about an 1/8 inch with a round file or die grinder.Bolt it on and bleed the system and its all cured.The suck thing is you cant use a rebuilt master cylinder because they dont come with a reservoir,and the stock reservoir from the 350 cylinder wont fit.The only way to get one is buy a new master cylinder that comes with the new reservoir attached.I got mine at O'reilleys for I think 119.I hope this helps with this underengineering problem on these years trucks.

 

Will this fit up to 96?

KO

 

What I would do is go to the oreilly website and see if your 96 uses the same master cylinder as a 92 does.If it does then you should be able to install the f450 master cylinder.

 

I used to have a 95 F-150 that did that. Pretty annoying, especially when the ford dealer wants to dock you trade in cash on a problem that's apparently their fault. Nice to know there is a solution.

 

WOW now that I have read all these questions and answers and recomendations I still have no clue to what the fix is for this problem of sinking brakes!Did you put a f-450 master cyl on your truck and fix the problem?Who said it was the booster and replace it and that was for sure the problem?I just dont get it! IS THERE A FIX OR NOT! If the truck had brakes for 15 years with a stock master then why is it that you can only fix this problem with a f-450 master when it starts sinking the brake pedal?? If it cant be fixed with another master cyl (new) stock type then why not take it to the dealer and have them replace the entire braking system with a new one as it would be a saftey concern that their brakes must be recalled because the f-450 master is not to belong on our trucks?YES my truck is doing the same thing and I am going to try a new master tomorrow FIRST (stock type).

 

The fix is the f450 master cylinder.I tried 2 different brands of the stock type ,they didnt help a bit.Others on here have replaced multiple stock master cylinders and about every piece in the braking system and still have the problem.I did the same thing .Nothing helped.Then I talked to the local brake specialist that has installed this modification to many local fleet trucks and solved this problem.None of the trucks that have had the larger master cylinder have came back complaining.It sure fixed mine .If you compare the stock master cylinder on a one ton to the half ton trucks you will see that most have the 1 1/16th bore cylinder.It sure stand to reason the way larger volume system with dual piston calipers and large rear wheel cylinders of a heavy duty one ton should have a larger bore master cylinder than a light duty pickup does.I am just trying to save the next guy with this problem the time and money of replacing a bunch of parts that dont need replacing and wont help his problem.Its too easy to just get the 450 master cylinder ,file out the holes a little and be done with it.

 

Well I went to ask the brake guy that has solved every brake problem I have ever had.He told me in 30 seconds what the fix is.He has seen this problem quite a few times on local fleet trucks.It seems the front calipers flex and the stock
1-1/16 bore master cylinder ,that is the same size as a half ton master cylinder by the way,doesnt move enough fluid per stroke to completely engage the brakes when they get this age.
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OK this is what I did.I went and got a new f-450 master cyl.3 new flex hoses ,all new lines front and back, all new rear brakes,cyl,springs, shoes,and front pads,booster ,and valve on frame,and started with 2 new stock masters,front calipers.
After starting with the new stock masters and nothing helped I went to the f-450 master with no help then replaced everything else but the front rotors.still nothing helped so i sent the truck to ford and was laughed at when i told him about the f-450 master.he said what I said its not needed.However if our brakes flex with age and you then replace the system with all new system then there is no flex in the system CORRECT.The brakes worked fine for 15 years with a stocker master so the
f-450 might help some but not all of us.I will let you know what our ford garage says about this problem when I pick it up and pay the bill .
The laughs on me now !
will let everyone know what the fix is when i get her home.

 

Was the 450 master cylinder you tried a 1 5/16 bore size.

 

I ordered 1 for a f-450 super duty.Still nothing back from dealer about problem yet.Im sure curious about the prob.

I told them that I want the origanal master back on and if problem is not fixed i refuse to pay for it and i was not going to pay for new parts unless they are defect in which i will return any parts that are defect to auto parts store with my grand thought. LOL.and trust me I WILL.

 

Yeah I am curious also on your truck.Definately dont pay for new parts that you know you have replaced all ready.Most mechanics now just throw new parts at a problem and charge the customer for their trial and error.Im sure the dealer will tell you the auto parts store stuff is inferior,they always do.I have about 10 trucks and my buddy has about 10 and we maintain them with autozone ,advance ,oreilly and some napa parts and rarely have trouble.
That really makes me wonder what the trouble is with your truck since it cured all these local ones and mine easily.One thing , make sure the guys at the parts store ordered you a real 450 master cylinder.You know most of these guys at the chain stores know nothing about parts.Did you have to file out the mounting holes to get it on the existing booster and it should say 1 5/16 in raised letters on the side of the cylinder..I agree with you ,that brake system when replaced with new parts as they wear out should work for more than 15 years,you never hear of this stupid problem with any other vehicles.A guy definately shouldnt have to upgrade his system just to keep the thing working.

 

For whatever it's worth I managed to get rid of 50% of my issue by properly adjusting one of my drums.

 

I adjusted both mine out until the rear wheels would would barely roll and it didnt help me.With the stock 1 1/16 master cylinder it was like right at the bottom of the pedal strok it was just beginning to expand the wheel cylinders and pistons.Right when the brake pads would hit the drum or rotor the pedal was at the end of the stroke and on the floor.I guess thats why the larger master cylinder worked on mine ,It just moves more fluid per inch of stroke.One thing I have noticed while looking up parts Is the above 9500 or so Gvwr trucks come with a 1 1/8 master cylinder stock and the lighter weight trucks come with the 1 1/16.My ton van is above 9500 gvwr and it had a 1 1/16th on on it so maybe that could have been part of it.The brakes sure work good now though.

 

still no call from dealer LOL I wonder what they are thinking LOL.yes it was a 450 master and yes had to ream out the holes.I agree with you that I adjusted the brakes till the wheel was locked up and still had this problem.I love my GM,s when it comes to brakes they have never give me this many problems the other thing about our fords are this dang abs light that likes to come on for no reason for us to put black tape over LOL.even though there is no problem I changed the computor under the dash ,rear end sensor and valve on the frame with the same thing no fix so I fixed it and put black tape on it.That was my 91 f-150 4x4 by the way.

 

I sure am looking forward to seeing what exactly causes this problem on these things it sure doesnt make any sence.I bet that dealer has a time figuring out your truck .
I a gm guy when it comes to gas trucks for sure but I have all these ford bucket trucks.It seems like fleet trucks are fords .This is the first newer
generation with the plastic resevoir I have had though.Never had any trounble with the 85 and back brake systems.Except those f600 wheel cylinders that are crazy expensive.

 

YAHOO !!! IT's fixed well here it goes,I had replaced all the brake components with no cure dealer called me today and said my truck was done.I picked it up and they put my origanal brake master back on and went through everything that I had done and could see nothing wrong ,they then started a brake isolation for each wheel and found out what the colprit was.Here it is ,,1 of the new calipers on 1 side was malfunctioning and when tested they found that 1 piston was working properly and the other 1 was slow to come out as if it was sticking or seizing so they replaced it with another new 1 and BINGO the brakes are better than when it was new,mind you they should be EVERYTHING is new.So if you have dual piston calipers on your truck and have this problem check here first.By the way I returned the caliper and gave them a piece of my mind as well.Thats our rebuilt junk we get.If we wanted that junk back we would have kept it,Its no good when we replace it so why sell it back to us,I just dont know.Anyway thats all for now folks till somthing else goes wrong.