1994 F250 diesel brake problem

JDEM

Well-known Member
My 94 F250 has been in my shop all winter, up to now. I take it off the road when the salt comes, so no hurry. Well, except I'd like to get it the heck out of my shop and be sure it is ready to use come spring.

I did a LOT of work on it. I have been neglecting many things for years. This last fall, when it would barely steer when turning left, and the brake pedal was going to the floor - I finally put it into my shop.

So - my only problem now is the brake system. Note - all is new or rebuilt. Rebuilt calipers in front. New wheel cylinders in back. New master cylinder. Rebuilt brake vacuum booster. New vacuum pump.

I have not really driven it anywhere yet except up and down my driveway. Brakes work good when I first use them, but with repeated use - the pedal goes near to the floor and the brake warning light comes on.

Note - that unlike gas trucks - this has a low-vacuum sensing switch and turns on the brake warning light if vacuum gets too low. I have determined it IS low vacuum making the light come on. Why - I have no idea. I have vacuum-leak tested everything.

I think - but do not know for sure - that excess brake pedal travel is using more vacuum then the vacuum-pump can sustain? This is something I never had to think hard about before. I am wondering if it is possible if the brake shoes in back are not adjusted tight enough and excess travel can do this? I was pretty careful adjusting them (I think) and they are self-adjusting anyway if I drive it around a little.

The soft brake pedal has me perplexed. Absolutely no air in the system. Rock hard when I first stomp on it - but if I hold steady pressure on it - it slowly goes nearly all the way to the floor. It did this before with the old master cylinder. It now has a brand new one and is doing the same. I guess the new one could be defective, but I am doubtful. I just ordered another one to try anyway.

If anyone has any ideas - chime in. I am almost at the end of my rope with this one. Such problems are usually easy fixes.

By the way - I do not need one right now - but I was surprised to not be able to find a new low-vacuum sensor. Seems Ford used them as well as some Dodge-Cummins trucks (with vacuum boosters). Looks like the part is pretty much unavailable for either which is kind of surprising. Ford # E3TZ-12A182-H . Chrysler Part # 04428676.
 
Nothing unusual about NEW parts being defective. When I worked at the car dealer we dealt with this a lot. And master cylinders were one of the biggest problems getting a good one especially from aftermarket.

So did you get the transmission problem solved ? It was this truck was it not ?
 
My vote is for the master cylinder. Hopefully the new one you ordered will solve the problem.
 

One of the things I would checks is MAKE SURE the rear brake are adjust close to the Drum.
#2 would be good pressure to the rear wheels when bleeding the brake.
 
I got sent four new solenoid packs and the 4th one fit. I am amazed at how difficult it was to find one with the correct harness plug. After I got the 3rd one that did not fit, I called the company directly - Transtar in Flint, Michigan and that is how I finally got one to fit. Transtar does not sell to the public so according to them, I was kind of "breaking the rules" by calling them. The transmission place in Flordia who was paying for all the solenoids called me up a little concerned since they got a bill from Transtar for around $1000 in solenoids. I could not return the ones I did not use to Transtar because they would not just take my word for the fact that they were never installed or used. I finally shipped them back to Florida and hopefully the transmission place can find a way to get full credit for them. I have to give them credit. They worked pretty hard to make this right.
 
Sad part is I doubt anyone followed up to correct the part info and assign them different part numbers so as to prevent this in the future.
Good thing you found a phone number ! Lots of places don't even list an address or phone number or their websites.
 
I suspect master cylinder.

IIRC, there was a post on here a while back about a master cylinder that would be damaged if stroked all the way to the bottom of the travel...

Don't recall what vehicle it was, sounds like a bad way to design something, but might be worth looking into.

Is there a proportioning valve in the rear brake line? If the shoes are out of adjustment, it may be closing the fluid down to a very slow flow. You could jack the rear up, idle in drive, hit the brakes, see if the rears are applying immediately or only after the pedal is near the floor.
 
Verify the bore on the master cylinder. Ford changed from a 1.125" to a 1.25" on these trucks during that time frame. Some may have the one from the F-450 which has a 1.3125.

I ran into this with my 1997 F350 a few months ago. Was given the 1.125" when I needed the 1.25".
 
I'll second Davida's post. The bore was enlarged. Also there should be an ABS valve on the frame below the master cylinder that needs bleeding. They also go bad resulting in a soft pedal.
 
About for got that one.

After I bypassed the ABS valve and realized
mine was fine I got a 7/16 fine thread plug
and pluged the rear port up on the master
cylinder. For me this did not change a
thing. They I found 9/16 fine thread plug
for the front and thought my problem was in
the front system.

After going through the front and finding
nothing I realized the master cylinder was
to small and could not pump enough fluid for
the front calipers for the pedal to get firm
while the engine was running.

Engine off you would have thought everything
was wine.
 
did you check or look at the rubber brake hoses attached to the caliper if there 24 yeares old i would replace them, and replace rear wheel cylinders aswell, i vote you havea bad master cyl good luck.
 
No proportioning valve in back. No ABS in this truck either. Pretty simple system by today's standard.
 
Hello JDM,

First thing in the morning, start the engine and push down on the brake pedal and hold it. If the pedal slowly goes down to the floor, barring any leaks,you have a bad master cylinder,

Guido.
 
As to the lack of vacuum reserve issue, is the "tomato juice can" they used for a reserve vacuum reservoir down low in the LH fender liner area still in place and intact/not leaking, and tee'd into the vacuum line between the belt-driven diaphragm vacuum pump and the brake booster?

IRRC, there's a plastic check valve in that system, as well.

As to the warning lite sensor, there's a couple of dealers in the Ford parts system that still have them on the shelf, but (likely) for a pretty penny.

They turn the warning lite on @ 10" of vacuum, gonna guess some "digging" will uncover lots of sources for vacuum switches with a similar rating, but you mite have to change out the wiring connector for another style.
 

Does the manual tell you to bench bleed the master cylinder. If it does and you don't, that's the symptom you end up with. You can't get all the air out of the master cylinder at the angle its at after install.
 
My F250 truck has a plastic vacuum reservoir attached to the big plastic box that holds the air-conditioning evaporator. No metal "soup can" although I have seen them on many other Fords. No leaks. I leaked checked everything. I was sure, at first, I had a vacuum leak in the dashboard from my heater controls. I pulled a lot of stuff apart for nothing to check. I finally just blocked everything except for the vacuum pump, reservoir, and brake booster. If I hold steady on the brake pedal I have 15-18 inches of vacuum all day long if I want. If I pump the brake pedal, over and over,and push hard, vacuum drops near zero for just fractions of a second and then comes back up. It now seems to me when I pump, there is too much volume needed by the booster and once the reservoir runs out, the vacuum pump cannot keep up and the light comes on. I don't know yet, but I assume the excess stroke of the booster and too much pedal travel is the problem.

Did the same with the old master cylinder as with this new one. I bled the master-cylinder on the bench before installing. I ordered another new one and will see what happens. Unlike what some others have experienced here - I have never yet had a bad master-cylinder when new in the box. I have bought many el-cheapos from China and up to now -never had any issues. We'll see.

Same subject, but different vehicle - I have a 2002 Chevy Astro Van I bought as an insurance wreck. Brakes worked fine but the top of the brake master-cylinder was broken off. So I got a new one for $25, bench-bled it - and put it on. No matter how much I pumped - I could not bleed it out. On that - to my surprise - I found out the engine has to be running due to the ABS. I do not know why since I have bled many ABS systems before without the engine running. But hey - what works, works. I started the engine and then was able to bleed the brakes just fine. I almost threw out that new master-cylinder thinking it was bad.

Note - I am on a learning curve a little behind modern auto tech. I never ever buy new. Just older vehicles. So at present - vehicles from the 80s-90s are "current tech" to me, and mid 2000 is "state of the art" since my newest vehicle is a Ford Escape AWD that I have never had to work on yet.
 
Well, now maybe I have exposed myself as an idiot. My Ford factory manual for 1994 says all the F250s have rear ABS. I
always figured because mine has an over 8500 lb. GVWR, the ABS was omitted. If mine does - I was unaware. I have been
under my truck many, many times and never noticed any sensors or modules. No ABS lights on the dash. I was totally unaware
until now. So maybe my truck has it and I never knew? If so, maybe there is trapped air in the ABS module? My manual shows
it as kind of hidden in the back frame rail. I have to go take a look and report back.

Thanks for all the input. Maybe I am getting senile. Buy hey -if I am, hopefully I will get too stupid to notice.
 
Are you SURE there isn't a metal vac reserve can just for the brakes (or supposed to be) in addition to the HVAC reserve canister on the passenger side?

A customer has a diesel F250 the same year as your's or possibly a year newer, and it has one, I can't remember exactly where, but on the driver's side fenderliner, possibly low down by the radiator support. Some years ago, it rusted out, causing a vacuum leak and we replaced it.

He is gone to AZ for the winter, so I don't have access to the pkup or I'd go take a look and refresh my memory, and/or take a pic.

Those little diaphragm pumps don't have a lot of capacity and a "reserve tank" probably isn't a bad idea.

Also, the hotroad parts sellers have electric-power brake vacuum pumps that run only when needed. Mite be something to consider.
 
No soup can in my 1994 diesel. My 1995 F150 with a gas engine has that big metal vacuum-reservoir on the passenger-side inner fender. My 1985 F250 with a 6.9 diesel also had that soup can. I cannot say for sure that my 94 once had one and it was removed way before I had it. I find no mention of it in my Ford factory manual. I don't find one listed at any of the on-line Ford parts places either. One of those things I never thought about until now. Seems it ought to have one. That is unless Ford chose not to use it with the dual-diaphragm booster?

I am thinking I might add one. I would love to know though if my truck ever had one. There is a vacuum manifold on the fenderwell. Has one unused port with a factory cap on it. All the others are used. One goes to the vacuum pump, one to the brake booster, one to the low-vacuum switch, and one to the AC and Heater blower/plastic reservoir.
a254264.jpg

a254265.jpg
 

My 95 does not have a vacuum can for the booster like yours comes off the pump to a manifold then to the booster.

Question what do you mean :when I fist step on the pedal its rock solid:

As in no power assist are a full pedal with power assist.
 

Let’s talk about my 95 7.3

It has the best brakes of any truck I have ever driven, If you just touch the brake pedal it imminently reacts almost like it has too much power assist. I just went out for you started it up held steady pressure on the brake pedal and the pedal sinks slowly toward the floor. I then pumped the brakes to see if I could run out of vacuum and yes I did. The brake light in the dash came on I think to warn of low vacuum don’t hold me to it.

I think the power assist is strong enough to drive through the master much like issues with some chevy trucks with a complaint of a soft pedal. I have never had a issue with a soft pedal it stops and holds with light pressure so no need to mash on it hard. I am gonna call mine normal and move on... I just did a 1K brake job on it , it better stop...
 
What you describe is how my truck has been for years. Great brakes but always had a soft pedal that fades if I hold down on
it. Up to know I assumed that it was not quite right and would fix it "some day." So now - after all new parts - it still
does it. Now - after hearing from you - seems either it is a common "problem" or maybe normal? I bought this truck with
200,000 miles and it now has 400,000 miles so I suspect a lot of work was done on it I am unaware of.
 

I can not say I have ever ran across this on a ford a chebby YES. The complaint soft brake pedal vehicle stops OK. None that I considered normal went all the way to the floor but close all stropped good. The booster is just that strong it will drive through the master cylinder. My Ford is not noticeable unless I just keep hard pressure on it I would have never noticed it till I checked mine for you. I have blocked off the lines on a cheby at the master the booster will drive through the master sounds strange but its normal. Most master issues accrue under light pressure before the cups get enoufh pressure to seal and overcome a slight leak at a cup in the master...

A bad leaking master will sink fast to the floor with no warring you have to let up and hit it again to get a good pedal. You would hit it harder than normal by d-fraught you apply enoufh pressure to over come a small leak at a cup in the master. Some are worst that others some can last years that way some you would be scared to drive it.

Stop by and drive my truck if it had anymore brake I would need to take some away from it... :lol: Lucky me the fuel pump I put on 1K miles ago is leaking again... So much for a NAPA pump that list it as supplied by the original manufacture...
 
With the engine running - when I first push on the pedal with moderate effort, it feels pretty firm and stays there. If I
push hard, it slowly fades near all the way down to the floor. If I then pump it, it uses all the vacuum and with a gauge
on it - vacuum goes to zero. It is the pumping that uses the vacuum. If I hold my foot down steady - even with the pedal
near down to the bottom, the vacuum comes right back up to 15"-18".

Note - the truck is in my shop. When actually driving - the brakes grab with such little effort - I just about never stomp
on the brake like this. That said - any other vehicle I have ever owned had a brake pedal that held steady and did not fade
(unless there was something wrong with it). I have a 1995 Ford F150 with a gas engine and its brake pedal will not fade
under pressure. I know the 1995 F150 gas-engine rig has a single diaphragm booster and also has a large "soup can" vacuum
reservoir. My 1994 F250 with the 7.3 diesel has a dual-diaphragm booster and no large vacuum reservoir. Just the little
plastic reservoir on the AC box.
 

I had to ask myself again why did my brake light come on after I pumped the ell out of it... I did not offer help when i first read the post because a master was recommended. Well just let him put one on if its a no go then I will ask a few questions. Most guys are looking for a EZ out so no need to get deep when they are going with the EZ answer lets call it human nature just like the human nature of me not questing why my brake light came on so took the EZ out...

Second page near the bottom seams to be the most logical fix to the issue... A large bore master cylinder I remember the issue on fords but don't know what models were effected so score a win for the one that posted it......



https://www.ford-trucks.com/forums/559273-brake-dilemma.html

https://www.markwilliams.com/index.php?seo_path=braketech

Problem Solved!

I've just been really busy for the past month and unable to post the solution for my problem.

PLC7.3 posted a TSB regarding the vacuum booster. I researched the TSB further and this is the complete TSB that I found;

Subject: Low Brake Pedal

Vehicle Involved: 1997 and Earlier F350 Diesel Power Truck with Vacuum Brakes

Condition: Brake Pedal is Low and Creeping / Falling to the Floor

Repair Procedure: Many owners have realized a low or creeping down brake pedal on their trucks. This condition may be corrected with several possibilities as solutions. Bleeding the brake hydraulic system because of air contamination. Adjusting the drum brake mechanism to correct the shoe to drum gap tolerance. Replacing a defective electro hydraulic dump valve because of a defective dump solenoid. In addition an approved Ford repair to increase the master cylinder bore diameter by using a F450 Super Duty master cylinder specific to the vehicle being repaired. Lastly, a new repair possibility exists involving the vacuum booster on a diesel truck. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found the condition is considered normal as the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds this condition unacceptable. This part is only for use on diesel-powered trucks P/N F5TZ-2005-CA it is not a service replacement, it must be ordered by the part number specifically, not the vehicle application.

Thus, this led me to submit another post "Diesel Master Cylinder" asking the general consensus on the bore diameter on the M/C for the diesel vehicles. Only one response.

I dug into my service papers and found a ford part number for a master cylinder that was replaced at the dealer years ago. I checked that number against what was supposed to be the original part number for the M/C and they didn't match.

What was the difference???

I took the original part number and cross referenced it in the NAPA web site and it returned the part that my local NAPA gave me when I replaced the M/C in December. This M/C has a bore diameter of 1 1/16" and was listed for a diesel powered vehicle.

I took the part number that I found in the service papers and did the same cross reference. This revealed a M/C with a bore diameter of 1 1/8" and was listed for a gas powered vehicle.

Now revert back to the above TSB. It talks about increasing the bore diameter of the M/C. It's all starting to make sense. Also, seeing Jeff Dodson's post about him using a F-450 M/C, which he drilled out the ports a bit, solved his problem.

I took my new M/C NAPA p/n 47-39634 and had them give me a new, not rebuilt, p/n 47-39635 M/C.

I bench bled the M/C with no foreign materials coming out of the bleed hoses, and installed it in the truck.

After bleeding everything, the pedal was nice and solid, just like the previous M/C. Here's the moment of truth. Will the pedal sink to the floor when the vacuum pump is supplying vacuum assist???

OF COURSE NOT!!!

The pedal performed just like it did before the rear steel brake line failed. I adjusted the rear brakes a little and off into the sunset I went!

If I never found the change in the M/C from the service papers, I would have went down to NAPA and gotten a F-450 M/C which would have been pretty much the same fix as Jeff Dodson, but I would be hesitant to drill out the ports from the start.

No misplaced brake lines. No problems with the brake hoses that were replaced two years ago. No air trapped somewhere in the lines after I've gone through a gallon and a half of brake fluid. No faulty master cylinders that contained metal shavings. No air infiltration from the threaded fittings. No problems with the RABS valve. I didn't have to replace the vacuum booster and vacuum pump. I never gravity bled the brakes either.

JUST WHEN YOU THINK YOU HAVE A WINNER


https://www.ford-trucks.com/forums/869589-soft-low-brake-pedal.html

"ZERO LOSS BRAKE BOOSTER"

https://www.ford-trucks.com/forums/661661-for-those-with-brake-problems.html

Ford also had a TSB Article 98-5A-34

https://www.oilburners.net/articles/fordpedalproblem.pdf
 
(quoted from post at 07:19:42 01/21/18) With the engine running - when I first push on the pedal with moderate effort, it feels pretty firm and stays there. If I
push hard, it slowly fades near all the way down to the floor. If I then pump it, it uses all the vacuum and with a gauge
on it - vacuum goes to zero. It is the pumping that uses the vacuum. If I hold my foot down steady - even with the pedal
near down to the bottom, the vacuum comes right back up to 15"-18".

Note - the truck is in my shop. When actually driving - the brakes grab with such little effort - I just about never stomp
on the brake like this. That said - any other vehicle I have ever owned had a brake pedal that held steady and did not fade
(unless there was something wrong with it). I have a 1995 Ford F150 with a gas engine and its brake pedal will not fade
under pressure. I know the 1995 F150 gas-engine rig has a single diaphragm booster and also has a large "soup can" vacuum
reservoir. My 1994 F250 with the 7.3 diesel has a dual-diaphragm booster and no large vacuum reservoir. Just the little
plastic reservoir on the AC box.

I am gonna call that normal and just like my truck that I have no complaint with the brakes. If I ever had to replace the master I would up-grade it to a bigger one (I think) I am interested in this
"ZERO LOSS BRAKE BOOSTER" more research need on it tho...
 
You did some impressive research. It is obvious now that I am not the only person with these brake issues. From what I
have read so far - Ford had complaints and nothing seems to be a guaranteed fix.

Using standard part numbers for master-cylinders - there is only one bore size for my truck. 1 1/8". I think F250s with the
smaller rear brakes have different master-cylinders.

Interesting reading but I am maybe more confused then ever. In my mind - a master-cylinder cannot "give" under pressure
unless it is either bad - or is designed to bypass under extreme pressure.

I am trying to find some 4" PVC sewer-pipe to make an extra vacuum reservoir. Cannot hurt to have one. I do not want to see
my brake warning light coming on under hard brake use. Making a reservoir by gluing two end-caps onto a chunk of PVC ought
to be easy, right? I see now that all the stores in my area only carry "hollow core" PVC not suited for any pressure. I
guess that means not suited for any vacuum either? Another idea is to use an empty 16 ounce propane tank.
 

The master cyl question would take some research it would be interesting to see what a few guys that (fix for a pay check) are hands on that post here have to say about it...
 

Been wanting to follow up on "drive through"

A quick test for this is similar to the booster test. With the engine off, stroke the brake pedal to dump the vacuum. If the pedal feels good without boost but you are able to get excessive stroke with boost, suspect excessive movement somewhere.

It could be a stuck brake caliper pin etc... Are the booster is strong enoufh to overcome normal stress points on the system "drive through" and you don't have a problem at all...

If I could just stop the fuel leak I have around the filter/canister I would be a happy camper... :twisted: :evil:
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top