I'm having a bugger of a time. My 1999 E150 failed inspection because the brake pedal was going almost to the floor. They said it could be the Master Cylinder. I reviewed the shop manual and performed the MC test. It passes the recommended test. That is I put plugs in the outlets of the MC and the pedal barely moves even when the engine is running. Therefore, no internal leaks in the MC.

Soon the pedal was going all the way to the floor. I began plugging the output ports of the ABS. With the lines to the front cylinders plugged and the rear connected, the pedal goes 1/2 way to the floor with the engine off and then 3/4 to the floor with the engine (vacuum boost) running. If I hook up either front line from the ABS to either front wheel cylinder the pedal goes to the floor. Thinking that the ABS was doing something to relieve the pressure I removed the ABS fuse. No difference.

So still suspecting the ABS, I built a bypass module. Now my MC connects directly to the wheel cylinders. Still the same problem!!!

NOTE I am bleeding the crap out of every line every time after I open a line. By "bleed the crap" I mean, I get some bubbles during the first two or three pumps, then none. I continue to pump for 15 more presses. That leaves me with about 1/2 the MC reservoir still full and I refill it at that time.

WHERE IS THE FLUID GOING??????????

It is killing me!!! It is like there is a balloon somewhere that blows up and collects the fluid then returns it when the pedal comes up.

Thanks,

Pete

 

Okay, it sound like the fluid is going somewhere, but WHERE? Is it leaking externally? Pull the hose off the booster and if the pedal (after a couple of pumps) feels just like it does with the hose connected, then go after a booster. Are the service brakes working at all? Are calipers moving, if the wheels are off the ground and the wheels are turned by hand, do they lock tight with someone pressing the pedal?

 

Since the above post I ran more tests. I can plug the MC and get solid pressure, engine off or on. I can commect the left front, right front and rear still plugged. I get 1/2 pedal solid, engine off or on. When I connect the line to the right front the pedal goes to the floor. Slowley when the engine is off and fast when it is on.

I replaced the right hose and caliper. Same. Suspecting I may have a bad caliper I got another one from another place. Same.

I can't find any external leak. I sprayed the underside with orange cleaner which seems to disolve brake fluid. Then I hosed it off and let everything dry. Then I spread dry newspapers under the lines, hoses and calipers. With the engine off I stood on the brake pedal for 2 minutes. The pedal went to the floor slowly and I could seem to pump it up. I went underneath and could NOT find any fluid. I started the engine and applied pressure. The pedal went to the floor.

I bleed everything forever anytime i open anyhting up. It acts like there is air in the system but I can't figure where.


To anwer your questions. I believe the booster is doing its job. Things tahe a lot more pressing and longer with the engine off than with it on. Calipers move and lock the wheels.

 

Ok, if you're totally positive that you don't have an external leak (check the steel line all the way to the caliper), then it kinda sounds like a oddball HCU problem (probably a isolation valve not closing). Can you pull codes in the abs? It might lead you to a resolution.

 

I removed the HCU and replaced it with some "Tees".

Before I did that I would get random ABS errors. Sometimes it would go for days without any ABS light. Then it would come on and there would be five or six errors. Next time, more random errors, some the same as last time and some new ones.

Like sometimes one of the errors would be "left front sensor error". Then the next time it would be not the left but the right one.

I got the feeling it as the electronic portion that was going belly up. Like there was a loose cable and or internal connection problem.

But the pedal, although was low (whether the ABS light was on or off) I still had pedal. Like maybe down to a inch from the floor.

Then the pedal started going to the floor and I decided to bypass the HCU altogether.

I wish I could post pictures here to show my bypass units.

Pete

 

I am still trying to find the problem. I am starting to think that the booster is moving, just a little, but enough to let my pedal go to far to the floor.

I am going to start a new thread asking folks to tell me what their vehicle does.

https://www.fordforum.com/forum/gene...383/#post62581

Pete

 

Mr petec , if the questions that I ask you seem dumb it's because I don't know if you checked the items.
Are the rear brakes disc or drum?
If they are drum, are the self adjusters working and did you remove the drums to verify this? You can bleed the brakes till the cows come home and the pedal is going to be LOW if the self adjusters aren't adjusting.
Next-- are you sure the caliper pins for the front calipers are allowing the calipers to move and aren't frozen /corroded.
I have experienced the problems you seem to be having and the questions I'm asking are what corrected my similar problems.
When you bleed the brakes manually , you need to pump the pedal SLOWLY to allow the M/C to refill correctly. You also need to wait a few seconds between bleeds.
It is problematic to try to bleed the newer systems the way we did the older systems. Everything has to be done slower unless you have a pressure bleeder.
If you aren't bleeding the brakes and you still have to add fluid, then you no doubt have a leak somewhere.
If you aren't bleeding the brake system and you don't have to add fluid then I don't believe you have a leak anywhere. You could have air trapped in the hydraulic system and that would give you a spongy/low pedal. Lets hope some light can be shed on your vehicle's brake problem with the questions I have asked.

 

hanky,

Drums on the rear. One adjuster was shot. But I adjusted both like we used to before they had self adjusters. Remember when that was one of the things you did every time you changed the oil? I do.

Calipers are working. I even replaced one of them along with the hose. But that was not necessary.

When I bleed I do it slow and after all the bubbles stop I run about 18 oz. of fluid through it to be sure. After the third master cylinder was installed all the bleeding was done, the pedal could still be forced to the floor. I cleaned off the underside of all spilled and sprayed fluid and spread fresh newspapers everywhere there are lines. Then I had my son pump the brakes (with the engine running and the pedal going to the floor) one hundred and fifty (150) times. Not a drop on the ground and the reservoir was still topped off. I'm sure there is no leak.

All the questions you asked have been asked by myself, a good retired mechanic, and a practicing mechanic that teaches vehicle repair at a community college.

My current theory is, when the pedal is pushed until the pads and drums cannot move any further, the master cylinder moves forward because the booster chamber walls are weak. This allows the pedal to go the floor.

As my son presses the pedal I can watch the MC (mounted to the booster bellows) squirm (the best word I can think of) and the MC move forward (away from the firewall). As I said, only hundreds of an inch, but more than on my car. Of course a car and a 150 are different size vehicles.

That is why I am asking people if they will watch their bellows and MC and see if there is any forward motion or is it really stable.

I hope this answers your questions.

Pete

 

As you know we can get so involved in a problem we overlook some things, so instead of telling you what to try , I will just ask the questions and you can check if you might have overlook any.
I'm not going to question the booster mounting since the vehicle is there and I am here.
If you bypassed the HCU and all related hardware and ran lines directly from the M/C to the front calipers and rear cyls and still only got 1/2 or less pedal, after pumping the brake pedal once or twice with the engine off that pedal should have been right up to the top and stay there. If it did not , did you check the brake pedal free ply at the M/C? When you adjusted the rear brakes did you leave a little drag on each wheel after pressing the pedal once to allow the shoes to center themselves?
Are the drums in the rear too thin, allowing the shoes to spread the drum?
What about the hose over the axle ?
There isn't too much to check regarding the front calipers, so if they were bled correctly and the hoses aren't ballooning I would think the pedal should hold and be right on top. Have you replaced any shoes or disc pads recently? If not, disregard.
You verified the MC will hold pressure with everything blocked, but is it leaking internally after the cups travel past the starting point? Brake pedal mounting OK ?
If you keep getting air each time you bleed , you just have a lot of air in the system .

 

"after pumping the brake pedal once or twice with the engine off that pedal should have been right up to the top and stay there"...But it isn't, it goes down to 2 1/2 inches from the floor. Up position is 5 3/8 inches from the floor. Even with the MC plugged at its output the pedal goes to 3 3/4 from the floor.

"If it did not , did you check the brake pedal free ply at the M/C"...I don't have any adjustment for that on this vehicle. If I push by hand I feel resistance after just barely any motion so I assume the free play is negligable.

"When you adjusted the rear brakes did you leave a little drag on each wheel after pressing the pedal once to allow the shoes to center themselves?" Yes, I turn them up until the wheel won't rotate then back off until it turns. Pump the brakes and repeat until I can just hear a little drag.

Drums have plenty of lining. Front pads are brand new.

No hoses swell at all. I hold them in my hand and feel for any expansion. I replaced the Right Front during this process.

I bought and installed a NEW (not rebuilt) MC. As I worked my way through this (I started April 27th) I decided that this second MC must be bad so I got another new one from another parts store. Exactly the same action.

I am attempting to attach a spreadsheet with the readings I took. I see that I have to zip it according to the rules of fordforum. Oops, still to large.

Try this link. http://home.roadrunner.com/~pjcalins...asurements.xls

Thanks

Pete