1956 Power Brakes

[VickyBlue]

Power booster was rebuild by the guy in San Jose, CA I can't think of his name. 3000 miles and counting. When the car is not running (engine off) I press the brake pedal, it moves, but it never comes back up. I try forcing it up, the pedal (plastic socket) disconnects from the shaft. As soon as I start the engine and vacuum is created, it is being pushed up and works normal. It has been like this since day one. I learned to just remind myself not to push the brake pedal after the engine is off, as the first time I realized this was happening,  the brake lights were on for 4 days and it drain the battery... I bled the brakes the other day and did it with the engine running. Brakes work normal, as normal as anyone can expect a 4500 lbs car stop on Raybestos shoes doing 90 mph...

Any idea what causes this and how to fix it?

[buick5563]

Are your brakes adjusted tighter than you would think "normal"?

Like 6-7 clicks instead of 12 that the manual suggests?

I would start there.

[JohnD1956]

I do not know brake booster theory but in the imagery sense, it would seem to me that the vacuum in the booster would come into play as you push on the pedal.  Since vacuum is pulling your pedal off instead of on it would seem that vacuum is in the wrong area of the booster, if at all possible. 

 

Other components involved may be flexible lines or even hard steel lines internally corroded, but didn't you already replace all or most of that? 

 

BTW,  I was driving my 56 the other day when I had to make a panic stop. I wasn't doing 90 MPH but I was thinking afterwards that I was sure glad I put those seat belts in.  That thing came down so fast I was a bit shocked. 

[VickyBlue]

Are your brakes adjusted tighter than you would think "normal"?

Like 6-7 clicks instead of 12 that the manual suggests?

I would start there.

More like 5 clicks... We do have seatbelt, 6 sets of them. All lines were put new back then.

Edited September 18, 2015 by VickyBlue (see edit history)

[Bhigdog]

Assuming that the brake lite switch is pressure activated like 1955 and 1957 the fact that your brake lights stayed on for 4 days leads me to believe you have a mechanical binding problem somewhere rather than a vacuum induced problem. Still, it's pretty weird.......Bob

[old-tank]

General question for the audience:  Is there a brake pedal return spring on a  56 other than the internal springs in the booster?

[VickyBlue]

Assuming that the brake lite switch is pressure activated like 1955 and 1957 the fact that your brake lights stayed on for 4 days leads me to believe you have a mechanical binding problem somewhere rather than a vacuum induced problem. Still, it's pretty weird.......Bob

After two brake light switches found to be leaking, I went manual. 

[Guest johnjackson]

Sounds like a binding issue. I would have a buddy sit in the car and press on them while you inspect the range of motion.

[VickyBlue]

Binding issue it is... But not external and I am not taking the booster off again. Once was enough. After studying the Service manual for an hour, I realized that I do not have the check valve that goes from the vacuum canister to the brake booster. Unless the valve is inside the vacuum tank, I do not have it. I also realize this is not the issue here. Took a little video of what the problem is. According to the book, the check valve helps in giving two to three "pumps" from air stored in the vacuum tank when the engine dies and brakes are needed. This was my biggest concern.  The pedal swings freely with engine running and disconnected from the the booster shaft. The guy that did the work was Power Brake Exchange, in San Jose, CA.

 

 

http://s412.photobucket.com/user/2xxnoxy/media/IMG_0229_zpsyg571a0y.mp4.html

 

http://s412.photobucket.com/user/2xxnoxy/media/IMG_0230_zpsq6o4rtoc.mp4.html

Edited September 19, 2015 by VickyBlue (see edit history)

[VickyBlue]

Drove off to the store, got a check valve between manifold and booster and tested it. Still the same... Don't know how long it takes for the canister to get filled up, since I never had a check valve before... Will take it for a long drive tomorrow and see what it does. Pedal got firmer though...Hope someone can chime in and tel me if the play in the brake rod is supposed to be there or not. 

[NTX5467]

Sounds like there should be something inside of the booster to return the internal linkage to the "un-applied" position in order that everything in the linkage stays engaged, engine off or not.  Possibly a spring with little "power" in it?

​

Once the brake linkage is depressed, a "reaction valve" should open to allow stored vacuum to move from the reservoir area to the "activation area" to provide the desired amount of braking effort assist.  Once existing vacuum (from the reservoir) is depleted (i.e., with the engine "off" and the brake pedal is depressed a total of two times), the brake pedal should still return to the unapplied position without any effort, just that the basic brake application will take much more effort to do, AND no pedal linkage disengagement from the booster should happen.  IF disengagement is happening and/or the pedal remains "applied" with the engine off, then something internal to the booster might not be operating "as designed".

 

I'm going on basic operational theory, although some specifics of that particular booster/vehicle might have some idiosyncracies I'm not aware of.

 

NTX5467

[VickyBlue]

I wonder which one of these might be...

 

[JohnD1956]

For whatever reason, I can't open your videos.  On my PC I get the Windows Media screen but all I see is a picture of a musical note and I can hear the noise of whatever you're doing, but can't see the video of the action.  Be that as it may, I am thinking AO, cause it appears that function is to hold the diaphragm against the front of the booster cylinder. However, they are all within the booster to begin with and the rebuilder presumably checked those.  Has the rebuilder offered any advice?  

 

If all that then are you sure the mechanical brakelight switch arm is not involved when the engine is off?

[VickyBlue]

I changed the link, let me know if it works. It has been more than three years ago. They were supposed to have it done in 5 days, they have had it for over three weeks. I called them and "complained" and the owner called me a Sunday morning telling me to be patient. I bit my tongue and hung up. So no... there is no advice offered from the rebuilder...

 

The mechanical break light arm is not involved. The pressure it applies is minimal, it is like pressing on a Parker Ballpoint pen.

 

On a second note, the check valve I installed last night, IT WORKED! I am getting three full pumps now with the engine off. 

[NTX5467]

If the external check valve worked, then the one internal to the booster might be having some issues.  Even so, the pedal and linkage should return to the "off/not applied" position on its own by itself.

 

Obviously your vendor was having some issues on HIS supply line during the rebuild.  Either finding a vendor that DID have something or he was having to get outside of his normal supply chain for one reason or another.  Be that as it may.

 

Glad what you did worked!

 

NTX5467

[SpecialEducation]

After two brake light switches found to be leaking, I went manual. 

 

 

I've considered the same thing.  When we had the master cylinder rebuilt, we changed the system to DOT5 (thus changed EVERYTHING in the system).  I don't know if the new pressure switches are set too high, or if it's the compressability of the DOT 5 (although I suspect the former), but you really have to cram on the brakes to get the lights to come on.  We've swapped it out a couple times and it's only marginally better.

We have a new mechanical switch, we just haven't fab'd a bracket for it yet...

[JohnD1956]

The new link worked, and I saw the video.  I don't have any idea what could cause this.   In your explosion diagram above, are BH, BK and BJ a vent mechanism on the end housing BE? 

[VickyBlue]

This is something Leif posted a while back... Thanks buddy... I am still not 100% sure which are the "dry" sections of the booster. The reason I sent it out to be rebuild was there was brake fluid out of the rear tiny vent hole. I do not know if this same vent hole is not venting now and it creates a problem, but I got it to work, I might add a second storage tank somewhere, but for all it matters brakes work as good as they will ever do.

[JohnD1956]

So, was the BH part, listed as a Check Valve, the check valve you installed?

[VickyBlue]

No. It was an inline check valve from the intake manifold to the booster, something like the one pictured. I did not have that valve and got a generic one.

Edited September 21, 2015 by VickyBlue (see edit history)

[JohnD1956]

After reading the manual it appears there are two things to check.  The easy one is the pedal adjustment. The mounting pin is an eccentric, and can be turned after loosening the lock nut. This adjusts the vertical height to be certain the pushrod is centered in the air valve.  Non alignment can result in binding upon release of the pedal.

 

The second thing is the return spring for the control valve. This would be item AN in the diagram above.  According to what I read, when the engine is off, depressing the brake pedal results in moving the control valve out of contact with the power piston.  The spring for the control valve is lighter than the spring for the power piston, so without the engine running it's easier to apply the brakes.  When the engine is started though, the vacuum pulls the control valve back into contact with the power piston.  This is what it looks like in your video.  During normal operation with the engine running vacuum may be pulling the control valve back to the power piston so you don't notice the lack of the spring.  that spring may be either broken or missing. 

[VickyBlue]

After reading the manual it appears there are two things to check.  The easy one is the pedal adjustment. The mounting pin is an eccentric, and can be turned after loosening the lock nut. This adjusts the vertical height to be certain the pushrod is centered in the air valve.  Non alignment can result in binding upon release of the pedal.

 

I finally got the time to get into this. The vacuum valve was working (and still is) but this is what I tried first, JohnD's suggestion to adjust the pedal. I did not know know the mounting pin was eccentric... I went over the whole brake system twice, never took the time to notice the actual movement of the pedal when the pin was moved... My pedal was off to the far upper right, turning the pin I actually saw it swinging down towards the center. I sat there for 5 minutes pressing it and releasing it... Never failed again...