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The other day i was testing my brakes for a clunking noise, but i noticed when pumping the pedal once every second, it started causing my idle to fluctuate. Is that normal or do i have a leak in my brake booster?
 

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Vacuum from the booster will cause it to flutter a slight bit. Also if you have any charging system issues, the off and on current draw from the brake lights could slightly pull the idle down.
 

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^Yes, idle fluctiation during brake application at idle is absolutley normal. It is a normal design issue which has much to do with the assist that the booster provides which operates under the principles of pressure differential between two distinct chambers in our brake boosters and the operation of the booster control valve.
 

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Wanna get scared? When you are under boost, try to brake. Dont lift off of the throttle, dont slam the brakes, but try to use them.

I havent done it before, but concidering the system works under vacuum, positive pressure would actually make the system work worse than if you had no booster at all
 

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Orion ZyGarian said:
Wanna get scared? When you are under boost, try to brake. Dont lift off of the throttle, dont slam the brakes, but try to use them.

I havent done it before, but concidering the system works under vacuum, positive pressure would actually make the system work worse than if you had no booster at all
That's what the one-way check valve is for. I believe the brake booster even stores a small amount of vacuum.
 

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Zach90Turbo said:
That's what the one-way check valve is for. I believe the brake booster even stores a small amount of vacuum.
Yep, you can feel it if you turn off the motor while coasting and then pump the brakes a few times. At first it will feel normal, but after a short time there is no help from the booster.
 
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