Brake Pedal Collapses?

[TTDRIVER]

Hey everyone,

When I push down on my brake pedal, it has pressure almost all the way and then it just falls out of pressure and collapses. I have no oil in the lines and the brake master cylinder is brand new. So basically lines and BMC are new with no oil. Is this normal or is something wrong. The only pedal I have as of now is only the air from the Brake Booster. Can someone help. This is the only thing keeping me from driving my car after 2 years.

Thanks

Saro

[jmortensen]

Search for "reaction disk" if you want the long version. Short version is it sounds like you dropped a little rubber disk into the booster when you were swapping the masters. You need to pull the master and look in the bottom of the booster, fish that puppy out and stick it in the center where the pin for the master cylinder goes.

[TTDRIVER]

Thanks! Do I need to remove the brake booster to help find the "reaction disk" or will I be fine just removing the Master cylinder? Also after I find it what do I do with it?

Thanks alot!

Saro

[TTDRIVER]

I look around couldnt find anything. Is it the rubber that goes around the rod that sticks out of the Brake booster?

[jurven240z]

I had a reaction disk problem for a few year and my pedal had no feeling until the bottom end of the foot travel. You stated

"When I push down on my brake pedal, it has pressure almost all the way and then it just falls out of pressure and collapses."

Was this with the engine running? Have you checked for leaks at the real wheel cylinders? Did you bleed the master cylinder on a bench vice before installing? Did you make sure the lines were installed in the correct location? On the master cylinder where the lines conect you will find the letters "F" for front and "R" for rear.

Where is the reaction disk? When you remove the master cylinder you see the rod coming out from the booster. This rod is what pushes against the master cylinder but at the other end (inside the booster) there is a rubber disk that tends to fall out if you pull out the rod. I had to remove the booster, pull the rod out by removing the rubber/plastic holding disk (you see this outside the booster).

[1 Bravo 6]

Ummm,

Saro mentions;

I have NO OIL in the lines and the Brake Master Cylinder is brand new. So basically lines and BMC are new with NO OIL.

I take him to mean BRAKE FLUID ?????????????????????????

Rick.

:devious: :devious:

[xray]

I agree with jurven240z. I had a reaction disk problem 4 months ago, and the problem was not as Saro describes. In my experience, dislodged reaction disk causes no brake engagement until the end of pedal travel, not sudden loss of pedal pressure while braking.

I am also curious as to what "no oil in the lines" means. If oil=brake fluid, then the answer is....put in some brake fluid, or find the leak and fix it. Or rebleed the system. Again. And again...

Steve

[jmortensen]

I agree with jurven240z. I had a reaction disk problem 4 months ago, and the problem was not as Saro describes. In my experience, dislodged reaction disk causes no brake engagement until the end of pedal travel, not sudden loss of pedal pressure while braking.

I am also curious as to what "no oil in the lines" means. If oil=brake fluid, then the answer is....put in some brake fluid, or find the leak and fix it. Or rebleed the system. Again. And again...

You know you're right. I think I misread his original post. I thought he was saying that his pedal went most of the way to the floor with no brake engagement.

The typical master cylinder test is to step on the brakes with a light pressure. Usually a bad master will let the pedal slowly fall to the floor. Then if you hit the brakes really hard the pedal will hold the pressure. Try that and see what happens.

If oil=brake fluid then he obviously has another problem of the fluid leaving the system somewhere. Could be the master leaking into the booster or one of the connections in the hard lines or a bad caliper or wheel cylinder.

[TTDRIVER]

Thank you all for your help. Sorry for not being clear. All the brake lines in the engine bay are new with no brake fluid in them yet. The original problem was that I was attempting to bleed the master cylinder but could not get the rear reservoir to get any fluid out. So I went and purchased a new master and replaced it. Before this point I did not have the problem described in this thread. As soon as it was installed, I went and pressed on the pedal and noticed that it felt totally normal 75% of the way down, but then it lost pressure and it collapsed. The normal feeling I'm describing is basically the pressure from the booster. I also noticed that the master cylinder was not an air tight fit on the booster so it was leaking air. Now I have gone and ordered a new brake booster so that all is new. I will reinstall everything and see if the problem still exists.

[beandip]

Hey everyone,

When I push down on my brake pedal, it has pressure almost all the way and then it just falls out of pressure and collapses. I have no oil in the lines and the brake master cylinder is brand new. So basically lines and BMC are new with no oil. Is this normal or is something wrong. The only pedal I have as of now is only the air from the Brake Booster. Can someone help. This is the only thing keeping me from driving my car after 2 years.

Thanks

Saro

Saro first do NOT depress the brake peddle untill you add brake fluid ! Do not ever pull the rod from the booster, if you do the disk mentioned above will fall from its position and the Booster will not work properly. When you install a new master cylinder bleed it first before you install it . then connect the lines and bleed the brakes starting with the right rear then the left rear then right front and the left front last. Do you know how to bleed the brakes ? Gary

[TTDRIVER]

Hey Gary,

If it's the same as bleeding the clutch but in the pattern you mentioned then yes. If not, then I'm going to have a mechanic shop do it just because it involves stopping the car and my safety. As far as the bench bleeding of the master cylinder, can't I just install everything and bleed it from the actual master cylinder bleeder valves. I never understood why this should be done off the car. The funny thing is when I removed the old master cylinder I pulled out the rubber around the rod in the booster

and the pedal felt normal. Anyway I'm going to pick up the new brake booster today and try to install it all. Can you get back to me regarding the bench bleeding. I really appreciate your help.

Saro

[beandip]

One thing I remember you said that there was no seal between the master and the booster . There isn't supposed to be. I think you are correct about taking the car to the shop and having them bleed the brakes. From what you are asking and the comments made. It is appearient that you don't have the experience to do this with out help. As you stated this is a vary important part of the car . It must work no ifs ands or buts . GAry