01 V70 Vacuum leak

Discussion in 'Volvo V70' started by Arnold, Sep 20, 2007.

  1. Arnold

    Arnold Guest

    Hi there !! My new (to me) V70 T5 has a hissing sound in the cabin, which I
    suspect is a vacuum leak, took it to the dealer and they said that the brake
    booster have to be replaced ($540 plus labor). I would like to plug the
    vacuum line that feeds the booster and make sure that the diagnostics is
    accurate/ Couple of questions:

    - The vacuum feed for the AC vent actuators, where is that coming from?
    - The vacuum hose that feeds the brake booster only feeds the brake booster,
    and not any other vacuum reservoirs, right?

    If this is a common failure, am I on the right track?


    Arnold, Sep 20, 2007
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  2. Engine vacuum.
    Again from engine vacuum.
    Usually the cause is some previous repair where the
    mechanics brakes the hose when repairing anything else.
    The less goings to the work shop the best.

    Basically you need to locate where is the hissing sound
    comming from. From the engine compartiment, or from
    the interior of the car.

    That's no vacuum pump, so that vacuum always comes
    from the engine intake manifold.
    JM Albuquerque, Sep 20, 2007
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  3. Arnold

    Arnold Guest

    Thanks for your reply, What I was asking was if the vacuum source for the AC
    actuators and the brake booster are coming from 2 different places on the
    intake manifold, so I could isolate the vacuum leak by plugging one hose at
    the time in the engine compartment. I could not do that if they were fed by
    the same point, and split with a Tee downstream, or if the actuators are fed
    from the brake booster. The hissing sound appears to be coming from
    an area under the steering wheel. I will not have access to the vehicle for
    another 7 to 10 days.

    Arnold, Sep 20, 2007
  4. Arnold

    Glenn Klein Guest

    Best chance that it is the brake booster very common complaint nothing
    to rebuild just replace the brake booster. The noise will get worse @
    some point & the power brake's will slowly start to get harder to press
    Glenn Klein, Sep 21, 2007

  5. Look, vacuum is changing all the time.
    You can have hard vacuum under heavy decceleration, and
    no vacuum at all when the turbo is at full pressure.
    So, the hissing sound must change accordingly.

    Hissing sounds may have many sources.
    You need to find the patern, when it changes sound, and so on.

    Brakes is hard to believe - large independent hose with an
    anti-return valve.
    The AC actuators could be, but again vacuum changes all the
    time inside the intake manifold.
    There is a small vacuum hose for the turbo indicator too.

    Are you sure it is a vacuum related problem?

    If its a gasoline car, usually vacuum problems causes the
    "engine failure" lamp to light (lambda sensor), due to
    a faulty air intake.
    JM Albuquerque, Sep 21, 2007
  6. Arnold

    Arnold Guest

    Hi Mr. Albuquerque, you are correct, the hissing noise changes per driving
    condition, under acceleration, or when climbing a hill, it is barely
    perceptible, however, when the car idles, it is very noticeable. Have not
    had the "Check engine light on" yet, maybe the computer tries to compensate
    the mixture based on the O2 sensor, but I sure would like to eliminate the
    leak and avoid running it like this. Thanks a lot for your help. Something
    else I should check is if after I shut the car off, there is enough vacuum
    in the brake booster reservoir to apply the brake once, if I can, then I
    know for sure the leak is elsewhere because the check valve would hold the
    vacuum in the brake booster.
    Arnold, Sep 21, 2007
  7. If so, your vacuum hypotesis is quite good.
    At idle you get a steady situation with a good vacuum to test
    all the hypotesis of a leak.
    So, its a small leak.
    There are many small hoses hidden below the intake manifold, some
    go down to the turbo.
    The engine is very complicated to work with (very compact).

    Check the turbo indicator hose that shoud go up to the
    instruments pannel (I belive), since its a direct indicator of
    the vacuum and could be itself the responsible.
    And the AC actuators vacuum too.
    Brakes system is all inside the engine compartement and most
    certainly a small leak cannot be heard inside the car, since those
    cars are very well sound isolated.
    JM Albuquerque, Sep 21, 2007
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