1994 F250 brakes New questions?

I already have a post going on this issue but it is getting a little buried. I am looking for some "common sense" ideas or possible explanations.

This on my 1994 Ford diesel F250 HD truck (over 8500 lb. GVWR)

Truck had 200K miles when I got it and now has 400K miles. Brake pedal has always been soft. If I hold pressure on it steady, it will slowly go near all the way down to the floor and my low-vacuum warning light comes on. Has a vacuum booster.

Note - brakes have always worked great. Just kind of un-nerving to have a fading brake pedal and a warning light that comes on under hard use.

So - put it in my shop this winter and replaced near everything. STILL has the problem. New master-cylinder, rebuilt calipers, new wheel cylinders, new vacuum pump, rebuilt vacuum-booster.

I now find out that many Ford owners with similar trucks had or have the same complaints.

Ford Motor Co. addressed the issue with two items. #1 is a special "zero loss" brake booster only for diesels. #2 is a larger-bore master-cylinder from a F450.

I have read many posts where various people tried the Ford fixes. Some said they saw improvement and some not.

I do not like changing parts unless it at least first makes sense in my head.

How can any master-cylinder allow brake-pedal fade unless it has a bypass circuit allowing brake fluid to get past the pistons? And hey - maybe the OEM master-cylinder does?

Ford came up with what they call a "zero loss" vacuum booster only to fix problem vehicles. Loss of what? Vacuum?

One more item to enter into what so far, is a mystery to me. I have read many posts blaming the ABS valve. I just found out my truck does have rear ABS with a module in front. Before yesterday, I did not know it existed. Problem is - as I see it is this. It only has two brake line ports. An "in" and "out." So it seems all it can do is turn "on" or "off" the rear brakes. It does not dump fluid anywhere. I do not see how this can possibly permit brake pedal fade regardless of what it does.

Like many problems that get posted on Web forums - I see lots of ideas but have not found any posts were someone says - "hey, I fixed the thing."

Here is the Ford bulletin info for 1997 and older diesel trucks:

Many owners have realized a low or creeping down brake pedal on
their trucks. 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.

I'm still running this vintage truck on my farm, I've three right now, all from down south to have decent sheet metal. I've been running these, diesel and 460 since 1989. Looking back thru my notes I had this issue of sinking pedal, 3 different times. All 3 were due to pin holes in my steel brake lines. 2 were in the left rear, where the steel lines run along the frame. Farm in on gravel, 10 miles to pavement, so between mud stuck up there and normal winter salt usage in MN, they lay buried. The 3rd was a pin hole in the steel line in the RF where it joins with the flex line. I was using a bit of brake fluid over time but attributed it to the vacuum part of the power brake system. These were true pin holes and under light, or normal braking, the only sensation was a mushy pedal. I had a issue one time where I had to stop quick, pulling a loaded trailer. Mashed on the pedal and blew the line and found the problem. Luckily, for me, the ditch was open and I avoided a rear ender, I had enough momentum to drive out of the ditch.

You know, I've had this problem with my 96 F250 PSD pickup for a while now. Mine isn't so bad like yours where it'll set off a light, but it does have pedal creep or a soft pedal. Been that way for a long time, doesn't seem to affect my braking, but that soft pedal can be a little hard to get used to. Mine still has all original parts, and is at 300,000 miles. Sometime soon I'm gonna go with the F450 master cyl and the zero loss booster. Like the other posts you find about it, we'll just have to see how it works.

Poster below mentions pin holes in brake lines. If this were the case, you would be losing fluid. Are you?

I have an 89 F250 that was my company's plow truck for sixteen years. Now it's reduced to plowing and firewood only but I've had occasion to replace nearly all the brake lines as they rotted away, so they're all in great shape and my pedal does the same thing.

If the fading pedal is caused by the brake vacuum brake booster then checking it with out any vacuum should make you have solid pedal but just further down the stroke than "normal". IF you still have a soft/creeping down pedal you have taken the booster out of the equation.

I have not owned enough Fords to be of much help. I have owned a lot of Dodge trucks and one of the first things I eliminate if they start having trouble is the ABS/load proportioning valve near the rear axle. They are trouble waiting to happen.

On your truck I would try making a short ling and use it as a jumper around the valve on the truck and see if you get better pedal when you do this.

Something else you can check.

Around the time your truck was made Ford was having problems with the firewall cracking and flexing, primarily on standards.

Once the cracks get bad enough the firewall will flex to the point that the clutch would not travel far enough to fully disengage.

It is a longshot but is it possible what you are describing as a fading pedal is actually the firewall bending when you push hard enough on the pedal?

I never cared about anti-lock brakes. Big waste of money and tech as far as I am concerned. After all these years - no tests have proven they make a vehicle any safer. Yet, we have them.

I would quickly disconnect my ABS module if doing so made any sense to me. It does not. Only has one input and one output. So it cannot dump brake fluid anywhere to make the pedal fade or get soft. Looks like all it can do is turn the rear brakes ON or OFF.

Just a update for anyone that cares. I took the truck out on the road for the first time and ran the brakes hard, up and down some long hills. It got a little better. Why? I assume the new brake shoes started to seat an self-adjusters tightened things up so there is less wheel-cylinder piston travel.

Now - after some hard use - brakes are mostly fine when going forward. Oddly, on a hill, rolling down backwards, and pumping the brakes - I lose all vacuum after three or four pumps. If I hold steady pressure on the pedal, the vacuum recovers. Not a huge problem - but if right - kind of a poor system design. Why it is more of an issue in reverse then forward is kind of perplexing.

I am off to Home Depot. I am going to buy some 4" PVC and caps to make a vacuum reservoir and see if it improves things. Might make things better or maybe worse? Seems if my truck needed a large reservoir- Ford would of used one like my F150 gasser has?

Easier to just try it then sit here and think about it. Will report back.

Going backwards often changes the aggressiveness of self servo action so more pressure might need to be applied. If a pedal fades to the floor, and fluid is not lost, The MC must be at fault. There should never be a return line on an MC. Jim

Yes it does. It dumps internally. Has a piston under spring pressure that when electrically activated opens and lets fluid bleed off, pushing a piston forward. You can test these by taking the front plug out of the ABS module, having someone push on the brake while you put your finger against the piston to see if it moves. If it doesn't move it is not bleeding through. If it moves, replace the module.

Further, these model's pedal will sink if the engine isn't running producing vacuum. To evaluate how the brakes condition is, drive it. Will almost always have good brakes with no fade. Have had lots of complaints over the years of '88-94 ford and econoline brakes not feeling right. The only question is, do they work and hold.

Did you ever go back and check the rear adjustment?

That's all I can think might cause a different pedal going backward, the shoes shifting because the tops are not against the pivot.

Do you think the rears are working?

When you were bleeding, did you open the rear bleeders while holding the pedal down? And if so, did you get a good flow and pedal drop? Could the ABS be causing a restriction? If flow to the rears is restricted, tha may be what you feel as the pedal slowly goes down.

The only other way to test the MC would be to install plugs in the ports, see if it creeps with the plugs. If the warranty MC came from the same supplier, they may have made several defective.

I officially give up. Checked pretty much everything humanly possible without making this into a new re-engineering project. If my truck was the only one, I might feel different. Now that I know this is not uncommon in Ford diesel trucks older then 1997 -guess it makes me feel better. Truck had gear-oil leaks in the back axles and needed new brake shoes anyway. I am glad I did all the work - but as far as how it stops now? Pretty much just like it was before.

I put the new PVC vacuum reservoir on it and it got MUCH worse. Seems counter-intuitive except maybe now I know whey Ford did not use one.

Truck is fine, I guess. I used it for 200,000 miles this way. I doubt I will live long enough for another 200,000 miles. So - rare for me - but the HECK with it. My father-in-law is a retired Ford engineer and I feel like yelling at him. But he is over 80 and senile. He would have no idea what I was complaining about and would not care either.

I am out $14 now for my vacuum-reservoir creation. Oh well, half what it costs my family to go to McDonalds.

Feels like a new truck now otherwise New suspension parts. New steering box and pump. New radio and antenna. New deep-cycle battery wired in back with two 12 volt power outlets. Hooked to an isolation relay up front that keeps it charged. I use it all summer with 12 volt refrigerator in back. Plus use the outlets to charge my 18 volt power-tool batteries when working all day in the woods.

We worked on the county ambulances,all 350s, all diesels. Same complaint on all of them every time they hired a new driver, low pedal. I could slide or at least get the anti lock to kick in on everyone of them(gravel parking lot) All mid to late 80s E-350. The cure was trade them off. To check a master cylinder,any model any year,unhook the lines to the master cyl and plug them. About the easiest I have found is a short piece of brake line and weld one end shut.

In the last month I've had two parts store master cylinders that were defective. If the pedal keeps falling while you're holding it like at a red light, and you never lose any fluid, it's bypassing internally in the master cylinder. If the vacuum can't keep up, time for a new vacuum pump.