Brake booster nonfunctional?

Anybody seen a vacuum booster that doesn't boost but doesn't leak vacuum either?
Friend has a '79 and it has good brakes but no boost at all. I've pulled the vacuum tube off and I have good vacuum from the manifold and the check valve is working. It has obviously had the MC replaced but there's no obvious sign of fluid leak on the booster.
Thoughts?

bad floating valve

Time for hydroboost and actually stop the car.....:crutches::ghost:

Bad floating valve?

And 1) this project is on a budget, 2) fuck hydroboost.

clutchdust said:

......... fuck hydroboost.

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:harhar::harhar::harhar::harhar::harhar:

clutchdust said:

Bad floating valve?

And 1) this project is on a budget,

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Budget fix. Pull out the check valve and spray silicone lube all around inside. Put it back and work the pedal a bunch with the car running.

Guys, update.
I disassembled the booster and the diaphragm is fine. I was surprised by that. Anyway, there is no leak unless the brake pedal is depressed, then I get a ~200rpm rise in engine speed. We also swapped out the check valve for a known good one, but even the old one seemed to be sealing just fine.
Back to the floating valve, not even sure what that is. Other ideas?

The floating valve is the plastic thing in the center o the diaphragm, where the pedal rod pushes on.

and yeah, f hydroboost

Hydroboost....it works, vacuum sux.....

CASE CLOSED.....some of you maybe read of my first hand experience and so know why I feel this way....

:smash:

bandaid for junk brakes

I've sometimes wondered about mine---same symptoms, and the brakes seem hard enough I wonder if I have boost. If not, then I'd love to go manual and get that huge booster out of the engine bay.

clutchdust said:

Guys, update.
I disassembled the booster and the diaphragm is fine. I was surprised by that. Anyway, there is no leak unless the brake pedal is depressed, then I get a ~200rpm rise in engine speed.

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So, if you are driving and have not used the brakes for a while, will they work? But if you try the brakes (within a few seconds), you don't feel any assist?

Twin_Turbo said:

bandaid for junk brakes

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Bandaid been fine for some 6? years now, very consistent and responsive without 12" of pedal travel and hollowing out the firewall for more pedal travel....

:rofl::tomato:

Twin_Turbo said:

The floating valve is the plastic thing in the center o the diaphragm, where the pedal rod pushes on.

and yeah, f hydroboost

Click to expand...

Marck, when I had the diaphragm out I looked at that. There seems to be a very small port inside, is that correct? Also, the rod that sits in there has something like 8 groves around it. Is that supposed to be sealed? Any break down of how that is supposed to be configured?

Just found this doing a search. Reads a little too techy for me right now. Probably will have to go through it two or three times before it starts making sense. I'm getting the concept, just not the real world configuration.
http://www.docstoc.com/docs/45365780/Vacuum-Suspended-Brake-Booster-Control-Valve---Patent-4399736