Hissing noise?

Discussion in 'General Chevy & GM Tech Questions' started by big bopper, Jun 18, 2010.

  1. big bopper

    big bopper Member

    1994 5.7 Vandura

    ok ever since i have had a top end re-build on my engine my cruise control has stopped working and i now have a hiss when ever i put my foot on the brake pedal, i dont have a servo (i think what i have is called hydroboost?) so its not that, i have been told the hissing is possibly somthing to do with the cruise control which is why the cruise control is not working?

    can any one tell me definatley what the problem is? and more importantley how to rectify it?

    thank you Tony
  2. dualdj1

    dualdj1 Rockstar 100 Posts

    Hissing is generally a vacuum leak. It sounds like you might have a bad brake booster; look at your master cylinder, there should be a vacuum line connection somewhere close by it, make sure that line is good.

    As far as your cruise, I'm not sure if that year used a vacuum driven cruise or electronic. If it's electronic, it's possible they didn't get a harness reconnected correctly. I would have to guess it's electronic, and that the hissing you hear is unrelated to the cruise problem.

    Hopefully someone with more experience on this vehicle can chime in.
  3. big bopper

    big bopper Member

    my van doesnt have the brake servo its got the hydroboost, so it's not the brake booster, it seems to be leaking air/ hissing from just above the brake pedal
  4. dualdj1

    dualdj1 Rockstar 100 Posts

    ahhh ok gotcha. I wasn't familiar with the hydroboost but understand it now.

    The hissing is only happening when you press the brake though correct? To me that means it's something related to the brake/hydroboost system. If you have no leaks and brakes feel good, then I would think the noise isn't a problem, other than being annoying. If you're worried about it, check with the company (this should be the correct link: http://www.hydratechbraking.com/)

    At any rate, The hissing should not be related to your cruise problem. if you had a constant hissing, then that could be a vacuum leak which (if your cruise is vacuum driven) could cause a problem with cruise. My guess is more that your cruise system is all electric, and you have a loose connection somewhere in the cruise setup. Double check all your wiring on the engine, make sure everything is plugged in well and the cruise control unit is properly connected to the throttle body.

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