Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Truck "whistles" on deceleration....

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Greg72, Mar 27, 2001.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,682
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    It's gotta be a vacuum leak I'm guessing...The whistling will continue as I coast down until I get to maybe 5 mph or less, and then it goes away as the truck settles into an idle.

    I checked the engine and there only appears to be one vacuum line that comes of the carb (Edlebrock 750) and goes back to a "T" connection which splits it, sending one line to the vacuum advance on the distributor, and the other line to a vacuum hookup on the transmission (TH350). Is that a correct way to provide vacuum to both parts? Is the vacuum strong enough using that method? The tubing is fairly small stuff....looks smaller than most fuel lines I've seen.

    There also appears to be a vacuum port on the manifold (Edelbrock Z-0?) on the passenger side near the distributor. Looks like a threaded plug that could be tapped for a vacuum signal also.

    Anyone with a BTDT story that could help explain what's going on with this noise?

    Thanks,

    -Greg72
    w/ Big Bad (and Whistling) 427 [​IMG]
     
  2. Burt4x4

    Burt4x4 3/4 ton status

    Joined:
    Feb 17, 2000
    Posts:
    6,854
    Likes Received:
    0
    Location:
    California (Modesto area)
    Re: Truck \"whistles\" on deceleration....

    Hmmmm, Ok I'm not sure that T is a good idea. I would use a dedicated vac line for both the dist and trannie. You want a vac source that will increase with the RPM, I'm sure your carb has two or three to choose from. The vac source on the intake is most likly for the power brake booster.
    I use the front vac source for my vac advance
    [​IMG]
    This is an older pic but you can kinda see the line.

    I would bring up the RPM and spray carb cleaner around the base of the carb and see if you hear an RPM change to try and locate a vac leak.
    Good luck

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    <A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>
     
  3. Steve_Chin

    Steve_Chin 1/2 ton status

    Joined:
    Mar 6, 2001
    Posts:
    1,126
    Likes Received:
    0
    Location:
    Foster City, CA, USA
    Re: Truck \"whistles\" on deceleration....

    Both the transmission vacuum modulator and the distributor vacuum advance cans should be hooked up to a manifold vacuum source. A tee that connects both of them together isn't necessarily bad, it's just not normally done. You should have another couple of vacuum lines as well. One should be for the power brake booster and one for the PCV valve. Do not, under ANY circumstances use a tee to connect them to the same port on the carburetor because the PCV will disrupt the brake boost.

    Speaking of PCV, have you checked your PCV valve to see if it is sticking open until you reach idle? They can make a wierd noise (kind of a muffled whistle) during high vacuum situations if they aren't operating properly.
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,682
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    Re: Truck \"whistles\" on deceleration....

    !! UPDATE !!

    I don't get to drive the K5 that much....but I did do a little tinkering recently and found that the PCV valve "rattled" when I disconected it and gave it a shake (which I was told means that it's functioning OK).

    There were a number of vacuum lines that had loose hose clamps. I went through and tightened a number of things up, and on my drive into work this morning the whistling is almost completely gone!!! There may be a bit more tightening to do on those clamps, but I wanted to send my kudos to Burt4x4 and Steve Chin for helping me get to the "source" of the problem.

    A lot of times on this list you read the original question....and a few suggestions for a fix, but never hear what finally happened to resolve it. In this case, it seems to have been loosely fastened vacuum lines to the PCV valve that were allowing air to leak and whistle.

    Just thought you'd enjoy hearing a success story.


    -Greg72
     
  5. Burt4x4

    Burt4x4 3/4 ton status

    Joined:
    Feb 17, 2000
    Posts:
    6,854
    Likes Received:
    0
    Location:
    California (Modesto area)
    Re: Truck \"whistles\" on deceleration....

    Cool Man![​IMG]
    You right, some problems asked never get the solution posted. Now we know that loose lines and/or a vac leak will and can make a whistleing noise!
    Thanks for sharing!

    Oh and how are you liking your K5? Don't you just LOVIT!!!
    I bet you have a list of thing that will keep you besy for the next oh....10yrs??? heheheh
    Late

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    <A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>
     
  6. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,682
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    Yep, I'm loving it!!!!

    It was a cool drive into work this morning, it's still not quite convertible weather....at least at 6:30am.

    But with that cold air, the engine felt STRONG....I love the sound of that big block when I romp on it!....especially going under the bridges....the echo is COOL!!!

    Makes me feel like a kid again!

    And to answer your question.....YES I have a big list of things I already want to do. It feels like I'm installing the entire ORD catalog on my K5!!!! Front & Rear Shackles, Steering Brace, Motor Mounts, etc, etc. [​IMG]

    It's going to be a fun summer...



    -Greg72
     

Share This Page