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1999 Nissan Almera N15

I noticed the problem awhile ago that occasionally the brakes wouldn't disengage. If I turned the vehicle off and pumped the brake pedal a few times the brakes would disengage. Now the only way I can get them to disengage is to turn off the car and disconnect the vacuum hose from the brake booster.

If you look at this diagram it looks like there is a check valve that maybe releases the vacuum pressure when you let off the brakes?

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Is there a way I can test this further, should I just replace the check valve, or am I looking in the right place at all?

Pᴀᴜʟsᴛᴇʀ2
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Robert S. Barnes
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1 Answers1

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The check valve is there to maintain the vacuum after the engine is turned off or during periods of wide open throttle where there will be little vacuum generated by the engine. So if the vacuum is still there with the engine off, then the check valve is doing its job.

Since your brakes are staying on, there must be air getting into the drivers side of the diaphragm (opposite side to the master cylinder). This is usually controlled by the atmospheric valve. Maybe this valve is faulty and is letting air in when it shouldn’t.

There is also a spring inside the servo (primary spring) that operates the atmospheric valve. If this spring is faulty it could also cause problems like this.

When you disconnect the vacuum pipe, you are letting atmospheric air pressure into the vacuum side of the diaphragm and so evening out the pressure on both sides of the diaphragm, which releases the brakes.

HandyHowie
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