Brakes work but pedal is soft

[Patcon]

I normally remove the metal retaining ring first with some picks. Then it should come out pretty easily

[Cooper260z]

Thanks @Patcon a pick did the trick! Now I’ll see if I can fish the disc out without  removing the booster 

[Terrapin Z]

4 hours ago, Patcon said:

I normally remove the metal retaining ring first with some picks. Then it should come out pretty easily

Thanks @Patcon I forgot about the retaining ring, it is not shown in the diagram.

4 hours ago, Cooper260z said:

so if I get the right grip and leverage on the pushrod, I should be able to just pull it out? It hasn’t come out so far from my pulling, and I obviously don’t want to damage the metal ring or rubber seal. 
If that’s the deal though then I’ll do my best to get it out. 

Looks like you were successful in removing the pushrod. I had a hard time getting the disc out of my booster with it off the car. I wish you luck. 

[Zed Head]

Just a thought, while things are apart - many/several of us have found machining grit in our various aftermarket hydraulic parts.  Slave cylinders and both type of master cylinder (clutch or brake), along with just bad seals from the start.  You might disassemble that MC and see how the seals and bore look.  It's pretty easy to do.  There are three seals, two to create pressure and one to keep the fluid in the cylinder if the back pressure seal leaks.  So you can have an internal leak - pressure loss, no obvious fluid leakage - without having an external leak - obvious fluid leakage.

Or, of course, just to be safe, you could replace it if you got it locally.  Even if you do that though, disassembling and cleaning before installation is a good idea.

Or, 2nd, you could just reassemble and see what happens.

[Cooper260z]

Took the booster off, thankfully it was much easier then what I’m used to with bmw 2002 boosters. 
Got the disc out, super glued it back on, put it back together and the brake pedal no longer goes to the floor! 
I’ll have to do some road testing and see if the push rod needs to be adjusted, but now I can comfortably start shaking the car down! 
Thanks for the help everyone, and I’ll keep faulty hydraulic parts in mind also. 

[Frankenstein]

Did this fix your problem? I think I am having the same issue. Bleed brakes with car off and pedal feels normal, start car and the pedal goes all the way to floor to stop the car. Always had awesome brakes until assembly after car restoration. Booster was taken off to clean and paint but never taken apart.

[Cooper260z]

@Frankenstein Yes this fixed my problem. With the booster off the car I was able to shake and look in it and eventually find the disc, then I used a long sewing needle to stick it and carefully extract it. Then super glued it back on to the push rod

[gundee]

I also had this same issue. Was driving me nuts. We took the booster off to attempt to open it up. It was then I could hear something loose.

We shook it and this rubber disc falls out. I'm going what's that?  I had to go to the manual to find out where it went.

Reinstalled and put everything back together. Wow what a difference. Back to normal again. Was very happy.

Don't know why the boosters were built with that piece installed loose and not fixed in place. Could have save many owners lots of trouble.

[Frankenstein]

Time to fish mine out 😩

[Zed Head]

Over the years I've always seen the reaction disc problem described as one where the brakes are either full on or full off.  I think that's why it's called a reaction disc.  I feel compelled to say that a fallen reaction disc causing the pedal to slowly sink to the floor just does not make sense, physically, mechanically, hydraulically, or any which way.  The actions of doing the work to take things apart, find the disc, glue it back in to place, and rebleed the brakes might be leading to better pedal function and brake operation, but there's no direct rational reason for the missing disc to allow the master cylinder piston to travel the length of the cylinder without creating pressure..

I feel better now.  Magic makes me nervous.  Be gone evil spirits!!

Edit - unless the missing disc causes the MC rod to "cokc", causing the piston seals to leak.  Maybe that's it.  Indirect effect.

Edited January 2, 2021 by Zed Head