1973 z28 350+.030 strange engine shake !

Discussion in 'Troubleshooting & Diagnosis' started by Lou6t4gto, Jan 24, 2018.

  1. Lou6t4gto

    Lou6t4gto Veteran Member

    299
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    Aug 18, 2010
    Ocala, Fla
    1973 z28 350+.030, 9-1 comp , 300hp 327 cam. w/Q-jet on performer. car Idles beautiful at 600 RPM, runs smooth up to 1800-1900 rpm when it actually starts to shake a little ! then pretty much smooths out again ! has 155 PSI in all cylinders and only has about 3,000 miles on it. like I said, it starts,& idles perfect, like a new car, but at 1800-1900, has a shake ! any ideas on what I can do to find the culprit ? has new 700r and converter, (not the converter). the harmonic balancer is old as the hills but not slipped. Help ! Thanks
     
  2. 70-camaro

    70-camaro Veteran Member

    1,402
    184
    Mar 25, 2010
    marietta ohio
    I was thinking balancer or flywheel.
     
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Is the shake the same driving, in park and in neutral?
     
  4. Lou6t4gto

    Lou6t4gto Veteran Member

    299
    12
    Aug 18, 2010
    Ocala, Fla
    that IS in Park & Nuetral.! does the same thing above 50.
     
  5. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    9,452
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    Nov 4, 2004
    Ringgold, GA
    Could be a couple things, first thing I'd check is to make sure the torque converter is tight on the flex plate. Check the flex plate for cracks while you're down there, but that's usually a different symptom, just a good time to check. You can't always tell by looking at the harmonic balancer if it's slipped or not. If it's the original 45 year old balancer, it's already lived a very long life. I'm just going to assume you've already checked all the pullies, nothing loose or out of alignment?
     
  6. Lou6t4gto

    Lou6t4gto Veteran Member

    299
    12
    Aug 18, 2010
    Ocala, Fla
    already checked the plate, conv, and pullies, all the pullies are now new as is the flex fan.
    18-1900 rpm wouldn't be a "Transition" from idle to main fuel circuits, would it ?
     
  7. 70-camaro

    70-camaro Veteran Member

    1,402
    184
    Mar 25, 2010
    marietta ohio
    I would buy a new balancer. Only thing left that goes round and round.
     
  8. Lou6t4gto

    Lou6t4gto Veteran Member

    299
    12
    Aug 18, 2010
    Ocala, Fla
    that was my thought. was just wondering about a "dead spot" in the carb.
     
  9. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    9,452
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    Nov 4, 2004
    Ringgold, GA
    Transition from idle to main circuit varies but it's in that range. It will not cause a vibration though, maybe a stumble but not a vibration. If you're thoroughly comfortable that pulleys and everything behind the crankshaft is in proper order, then replace the balancer and let us know if it cured the problem. Just for S & G's, try wiggling the fan front to rear, see if there is any slop in the water pump. You said you have a flex fan, so there is no viscous clutch to wear out.
     
  10. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    I've seen timing/ignition problems cause issues too.
     

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