Need help diagnosing a braking problem.

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RiskyDave

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Wise gentlemen and ladies of the forum,

Project Scarlett the “scumbag scamp” is off to a start. New front hubs bearings and some steering refresh have it back in the road and doing apocalyptic burnouts. However. I’m having a braking problem I’m having trouble diagnosing and haven’t been able to find on the forum.

I step on the brake and everything is fine till a certain brake pressure. Then the brakes seem to apply themselves all the way to a panic stop whether My foot is on the pedal or not. It sucks the pedal down and then holds the brakes if it’s own accord I till judicious throttle is applied or a combination of that and pulling the pedal back up with my foot. Front system discs have been entirely rebuilt with the exception of calipers. Booster looks new ish and master does as well, which is full and no leaks at any of the wheels. Drums look crusty but functional with no obviously leaking wheel cylinders. Any thoughts?
 
I think you have a bad booster. Control valve in the booster I'm not sure might be rod length/ adjustment from pedal / to master
 
I would take the vacuum off the booster and cap it. Leave the booster port open to the atmosphere.

If you experience the same issue it is most likely NOT the booster. But if the problem goes away then the booster has a valving issue.

It is interesting that you can pull the brake pedal with your foot and it releases.

But the fact that it self applies suggests the booster is the issue.
 
Pulling it back up with my foot may be giving me a placebo effect kind of reaction if I’m honest. It seems to help. But I’m also trying to give throttle at the same time so it may just be a coincidence on that side. I’ll try the vacuum plug and see what I get.
 
Went hunting fast for a replacement booster at all the part house websites... they look to be indefinitely out of stock most places? Does anyone know where you can get one if that is the problem?
 
In the Seattle area you should be able to find an old school local rebuilder. If it looks "newish" they may be able to replace the faulty part without a full rebuild. Years ago there were at least 1 or 2 places like that in the Spokane area
 
Check rock Auto etc for a rebuild kit.

Also if booster is issue and you give it gas your manifold vacuum will drop and might be releasing the brakes to some extent.
 
Power Brake Booster Exchange (aka Booster Denny) is in Portland, he's got a pretty good reputation.
 
What ever the fix turns out to be. Please come back and post all the gyrations. I think my brothers 73 Scamp w disc front/rear drum on a power booster master is doing the exact same thing. I have yet to dedicate a moment of time to diagnose anything and you could be a time saver. Good Luck for all our goods.:thumbsup:
 
without concern for safety//
poor mans line lock/launch control
 
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