brakes, again....

[mojavered]

Hey everyone!  I have had an issue of my brakes getting stuck on the floor, mostly after flooring it.  I have done just about all except the prop and residual valve.  Mind you, I can stop just fine and have no other issues with the brakes other than them not wanting to come off the ground, about to attach a spring to the pedal.  Booster holds vaccum, perfect.  Thought I was losing vaccum because the brakes will not work after hard acceleration.  But if I was losing vacuum, I believe the brakes would be harder to press.  No leaks anywhere, frustrated.  My back brakes are working just fine.  Any suggestions?

[Chryco Psycho]

the pedal should not need a spring , is the pedal pivot siezed , the pressure in the master should force the pedal back up 

[Bullitt-]

Lube on the linkage helped this guy http://www.cuda-challenger.com/cc/index.php?topic=71607.0

  Thought I was losing vaccum because the brakes will not work after hard acceleration.

   I wonder if a bad check valve could cause this. 

[Supercuda]

Incorrect booster pushrod length can cause these symptoms, too. Check carefullyfor any wear or binding on the pedal shaft,and for possible misalignment of these parts. Then check that the pushrod out of the booster is the correct length for your master cylinder. If these things are good, check for possible internal leaks in the m/c (a dropping pedal with no external leaks is the usual symptom). Duplicating your pedal application fo this step will also allow you to check for possible problems with the underdash stuff that you might have missed on your visual inspection.

[Chryco Psycho]

Bad check valve will cause no brakes after WOT , the booster should hold vacuum

[mojavered]

I checked to make sure the booster holds vacuum, good.  So I guess that means the check valve is good?  I was told there might be a clip on the booster rod holding things up, took it apart and there is no such clip.  I wonder if my new master cylinder is bad?

[Road_Runner]

The only times my pedal has ever gone all the way to the floor was when I had a bad master cylinders.  Does the pedal go ALL the way to the floor or just go to a point where the brakes are locked and then doesn't return?  If its all the way to the floor I wouldn't trust the brake cylinder very much, or you could have air in the system but not sure if it would still stay all the way down due to that.   

Later, Jim

[mojavered]

It does not go all the way to the floor, I stop just fine, the pedal just does not come back to me.  It does feel like it goes down further than it should.  All bushings are there and lubed.  I just replaced the vacuum/check valve.  I pulled the prop valve earlier and went and bought a flaring tool.  I will change the prop valve out and rid of the residual valve.  The master is new, but I think that I will take it and exchange it to see what happens, since it is already off.

[Moparal]

There is a big spring inside the brake booster itself. and also a rubber diaphram inside. It can have an internal leak and still hold vacuum. Does the brake pedal pull down by itself?

[mojavered]

No, only when I apply pressure.  I bleed the brakes the other day, again, and went to go for a drive and could not push down on the pedal.  Got out and looked around and saw that I broke one of the nipples off the vacuum valve.  Replaced it and still had the same problem as before, brake pedal would not come back up...Is there anyway to tell if your booster is bad? 

[Moparal]

There is a very small spring on the mechanical assembly under the dash that hooks to the brake swivel assembly on power brake cars only. But it sounds like a bad diaphram in the booster. Sometimes if you listen , you can hear a leak inside the car, but other times it is a dry rotted small tare inside the booster itself.  You should be able to pull a vacuum on the booster and it should hold vacuum to. If it doesn't , then it most probably is bad, or a rooten seal.

[mojavered]

I hooked up a vacuum gauge and pulled around 12-15 and it just held.  I did not want to pull anymore and destroy the diaphram. 
Can that small spring be seen from under the dash?  Or am I looking in the wrong spot?  I really appreciate your help!

[Moparal]

The spring may be visable to see, but it is around the swivel. Has someone taken apart the assembly before? That is about the only way it is lost by someone not paying attention to it's location. Most people dont even realize it is there. There is also different size check valves to. Can you hear it work when you push the brake pedal down when not running?

[mojavered]

I guess I am going to have to get a decent diagram of this.  When I got the car, the firewall was rotted out and the booster and everything was gone.  The bushings were there and in decent shape though.  I bought a new booster and MC and installed.  I do not recall seeing a spring though??  I guess I am confused on what the check valve is as well.  Like I said, I think I really need a diagram.  Here is the best diagram I have and there is no mention of a spring or check valve.  Hopefully it can be opened!

[Chryco Psycho]

the check valve is where the hose slides onto the connector into the booster
 the only springs I know of are inside the master cylinder