I came really close to putting a socket sized hole in my crankcase...

[AllDay815]

I posted up on here a few days ago saying i was having problems with my brakes and today I went to go get what everyone said was the problem, master brake cylinder, only to find out after a while of working that it still didn't fix the problem ... the brake still travels all the way to the floor before i get any resistance and braking ... which means that what i thought was the problem all along, power brake booster, is actually the thing wrong in the first place ... ....can someone please confirm this and please don't anyone say it can only be the master cylinder cause i did everything right on it 5 times today and have new pads and have bled the system ... which only really leaves the thing i said in the first place, power brake booster .... so can someone please confirm this that way i dont go crazy

[Nerd Racing]

did you bench bleed the master cylinder? I've never had one go on me but it is possible that the vac. operated spring could fatigue. how is the plastic check valve running to it? if it has a hair line crack that could be enough.

[AllDay815]

yupp i bench bled the master cylinder ... 3 times, just to make sure, and it still did nothing .... after reading up on a few other things on the internet, i am 110% possitive that it is the power brake booster

[AllDay815]

sorry i didnt see the other part of that post ... i dont know exactly what the vac line looks like i will check tomorrow ... but i do know that when i had the master cylinder off today, the booster pin had a lot of play and physically looked shot ...i have come to find out lately that the owner before me beat the crap out of this car

[mattdickmeyer]

bad brake booster usually causes rock hard pedal.

[mechanicaldj]

off the car, you cannot tell if the master cylinder is bad

unless if you plug the brake line holes and try to pump it.

I think you have a defective master cylinder


the brake booster only assists the brake pedal
and
if it goes bad the result is a much much harder pedal

[AllDay815]

thats not what every site i have been to says ... it says that there will be no resistance when you push on the pedal cause the vac seals don't hold the pressure anymore

[MTec007]

well in your other post you said it was wet between the booster and MC.. that means the MC was leaking fluid out, it was bad. whether or not the booster is bad (personally I'd listen to these guys, know all about these cars, but thats just me) is another story.

so to conclude you didnt was money buying the MC

[mechanicaldj]

as being a automotive tech since 1988

all I've been taught and experienced in all of the years since:

on a vacuum assisted brake booster, if you do not have any vacuum to your booster (as if the check valve failed or internal leaks)
your brake pedal will become rock hard,
it's like driving any old car with manual brakes

[mattdickmeyer]

booster failure caused by rupture or hole in vaccum diaphram listen for a hissing sound (vaccum leak) around the booster, put a vaccum pump to port see if it will holds a vaccum.

[AllDay815]

okay then i guess thats not it .. so what do you guys recommend to try now ... its got a brand new MC and its been bench bled 3 times

[JohnGunn]

It seems you are now reluctantly accepting that a pedal going to the floor is not a sign of booster failure. You don't need to go to the internet or trust the statements of anyone here to assure yourself of this. Your own common sense should be enough for you know such a design would be completely unacceptable.

When the engine is not running and generating vacuum the booster is disabled. If a working booster were needed to prevent the pedal from going to the floor, a car whose engine stopped running, out of gas, broken timing belt, blown engine, etc., could not be stopped since the vacuum needed to activate the booster would not be available, the pedal would go to the floor and the car would have no brakes. You can be sure no lawyer in the world would sign off on such a design. And if they found one who would, the first newspaper headline proclaiming "Family of Five Killed Due to Faulty Brake Design" would bring sales of that car to screeching halt.

But seriously ...

I agree with everyone else, it sounds like you did not correctly bleed 1) the master cylinder before installation, or 2) the system after the master cylinder was installed. I don't know how you bench bleed the master cylinder, but in that process did you actually see fluid moving out of the brake line connectors as you pressed the piston in? Also how could you have bleed the system after installing the cylinder if it was not pushing fluid through the lines? Did you get much fluid out at the wheels when you bleed the lines?

For the sake of completeness I should mention that the push rod, that sticks out of the center of the booster when the cylinder is removed, is adjustable. I suppose it would be possible that the length of that rod is not sufficient to reach the piston which pumps fluid through the brake system. There are instructions for calculating the proper length of that rod in the Ford Service Manual, but you should be able to roughly measure how far the rod protrudes beyond the surface of the booster and the distance from where the master cylinder actually contacts that surface and the piston recessed in the master cylinder. Just look at it and see if it looks like the rod is long enough to come close to the recessed piston.

This is not a likely problem, unless you have the wrong cylinder or the one you replaced was the wrong one for your car, and it was made to work by shortening the rod.

Now I'll tell you what I would do in you situation.

1. Go to Harbor Freight or some auto parts store and buy a combination Brake Bleeder and Vacuum Pump Kit like the one in the following link.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92474

2. Buy a large bottle of Valvoline synthetic brake fluid, 32 oz. size.

3. Remove the master cylinder.
4. Pour out as much fluid as you can.
5. Roughly estimate by sight whether the rod appears long enough to reach the piston recessed into the master cylinder. If it doesn't look as if the rod is long enough, stop and report back. If it looks close enough, connect the master cylinder back up to the booster.
6. Using Valvoline fluid bench bleed the master cylinder.
7. Connect the two brake lines at the master cylinder.
8. Check the fluid level in the master cylinder one more time.
9. Starting at the right rear wheel, follow the instruction in the bleeding kit to bleed that line until the old fluid is out and there are no more bubbles. Err on the side of too much to make sure the old fluid is all out. You'll have plenty of fluid left when this is finished.
10. Then bleed the other three wheels in the following order: left front, left rear, right front. Be sure to watch the fluid level at the reservoir to make sure it doesn't run dry after you finish each wheel.
11. At this point the complete brake system should be bleed, lines as well as master cylinder.
12. Slowly pump the brakes a few times until you feel the pedal resistance build up.
13. Top up the reservoir again and look for leaks.
14. Test drive on a street with no traffic.

I believe the synthetic fluid protects the rubber parts of the braking system. I replaced my original master cylinder at 180,000 miles and the rubber in the calipers is still original and dry. I replaced the back wheel cylinders at 60,000 miles when I bought the car, but they are still holding fine. Rubber is the weak link in all cars when it comes to trouble free operation over a long time. Anything you can do to extend the life of those parts is worth a lot. Not a place to spare expense. The $30 I am suggesting you spend is really an investment which will more than pay for itself, especially if you plan to keep you car running for as long as possible.

John Gunn
Coronado, CA

[scitzz]

What are the chances he has a leak somewhere? I did not read the last post, but yes, a leak at the MC/booster sounds like a bad MC to me....What if there is yet another one somewhere else? Rear wheel cylinder, etc?

Still, I would follow JG's post CAREFULLY before looking for something else.....

Don't get me wrong, and I don't mean to be rude here....

But you did come onto one of the greatest forums on the net, with some of the most knowledgeable people, who happen to usually be the nicest, to ask your question. When you get an answer, especially as well thought out, and as well written as Johns, then you might want to give it a try.....

Hope it all works out for you!

Paul

[JohnGunn]

What are the chances he has a leak somewhere? I did not read the last post, but yes, a leak at the MC/booster sounds like a bad MC to me....What if there is yet another one somewhere else? Rear wheel cylinder, etc?

No doubt in my mind the leak at the MC/booster points to a worn out MC. As for as other leaks, unless he is able to build up pressure in the lines leaks might be difficult to detect. Of course, if a line is ruptured that would keep the system from building pressure, but it would make a mess that would be hard to miss. And the level of fluid in the reservoir would drop noticeably.

But I agree with you it is a curious problem. You would think that even if the bleeding process was not well done and some air was left in the system, by pumping the pedal you would be able to compress the air and eventually feel some resistance in the pedal before it reached the floor.

I guess we'll have to wait and see.

John Gunn
Coronado, CA

[JoDan]

And if they found one who would, the first newspaper headline proclaiming "Family of Five Killed Due to Faulty Brake Design" would bring sales of that car to screeching halt.

Hey, Toyota is still selling cars