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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?

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  • Did someone fit the check valve in the wrong direction?
    – Solar Mike
    Commented Jun 30, 2021 at 12:04
  • @SolarMike No one's messed with it. I don't let anyone work on my cars if I can help it :-)
    – Robert S. Barnes
    Commented Jun 30, 2021 at 12:36
  • Maybe the internal spring of the booster is broken or got weak?
    – Martin
    Commented Jun 30, 2021 at 12:39
  • @Martin I don't know much about brake problems, just trying to find a way to diagnose this without throwing parts at it.
    – Robert S. Barnes
    Commented Jun 30, 2021 at 12:41
  • Do the brakes only stick on after you have have pressed the pedal, or are they coming on when you start the engine?
    – HandyHowie
    Commented Jun 30, 2021 at 19:22

1 Answer 1

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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.

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5
  • Yeah, I was coming to a similar conclusion. I'm guessing brake boosters are not serviceable, i.e. my only option is to replace it?
    – Robert S. Barnes
    Commented Jul 1, 2021 at 12:38
  • @RobertS.Barnes I don’t know how serviceable individual ones are by the DIYer. There are bound to be places that will service them for you, but it will probably be cheaper to buy one from a breakers yard.
    – HandyHowie
    Commented Jul 1, 2021 at 12:44
  • Well, a replacement shipped from Nissan Japan ( not including shipping ) is $638 on amayama.com - so if I can't find one in a junk yard I'm screwed.
    – Robert S. Barnes
    Commented Jul 1, 2021 at 13:01
  • Oh dear. Maybe you can do some research into the serviceability. You never know, there may be rebuild kits.
    – HandyHowie
    Commented Jul 1, 2021 at 13:27
  • There are rebuild kits on eBay, but the mainly look like they are for classic cars.
    – HandyHowie
    Commented Jul 1, 2021 at 13:29

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