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Discussion Starter #1
I've got a friend with a mid 90's Chevy van with an intermittent brake problem. The power brakes lose their power assist and leaves a very hard high pedal. Then for no reason the assist returns and it stops fine. The van sat for 3 days and when I pulled the vacuum hose off the booster hissed just like normal. Holding vacuum just fine. With the engine running when you press the brakes the engine speeds up briefly and then returns to normal. If you unplug the hose the engine speeds up and when you plug the hose with your finger the engine returns to its normal idle. I've had master cylinders go bad and leave a very low pedal but this pedal stays very high. Is there a valve in the booster that could stick? I don't want to tell him to replace something without being sure. Do boosters go bad and still hold vacuum? Thanks.
 

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pull the hose

off the booster I had the same symptoms and mine was blown bigtime, manually suck on it, its probably bad

S
 

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Discussion Starter #4
The booster will hold vacuum for days without running the motor. Can they go bad and still hold vacuum?
 

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The booster will hold vacuum for days without running the motor. Can they go bad and still hold vacuum?
I wouldnt think so.. But Im not all that up on brake boosters. How bout this. What if the vacuum line was becoming temporarily blocked, by say the check valve. So for the most part the vacuum is building. But then the check valve or some debris blocks the vacuum and then you get the hard pedal. Easy way to check this is completely bypass the original vacuum line with a new line and no check valve. Try it for awhile and see what happens?? JR
 

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Well

The booster will hold vacuum for days without running the motor. Can they go bad and still hold vacuum?
Concievably yes
You have the diaphram on one side, and the check valve ( if so equipped ) on the other, inline with the hose it should hold vaccum for a bit, not sure about days.
 
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