Drivetrain Vibration Questions

Discussion in 'Troubleshooting & Diagnosis' started by Glava, Nov 15, 2021.

  1. biker

    biker Veteran Member

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    The adjustable upper control arms gave mine nice alignment specs, but really showed up the play in my 3rd gen iroc box. I read somewhere that the 80/81's have good high speed aero. Certainly not as nice a look as the 70-73, but they manage the wind pretty well.
     
  2. ClassicRob1977

    ClassicRob1977 Member

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    Whatever came of this? I am having a SCARY vibration at 80+. I ran a bolt on coyote the other day and when I let off I was thinking I broke something. I have not even attempted those speeds since. I really need to figure this out..
     
  3. Glava

    Glava Veteran Member Lifetime Gold Member

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    OK, here is the recap of where I'm at;
    The tires have been road force balanced 2 times.
    Tires at 30 psi -no odd wear patterns etc.
    Rotated rims and they don't wobble or have dents.
    Rotated tires front to back etc. -still have vibration.
    Checked and verified front wheel bearing adjustment.
    Checked drive shaft, no spot that looks like a missing weight
    U-joints tight.
    No side to side or in/ out movement near rear of driveshaft.
    Again -this Z has 31k miles and I have serviced the front suspension regularly, changed rear gear oil/ posi additive at least 3 times.

    I finally got the Tremic APP and checked the pinion angle -checkmate 201, I think that you had mentioned this first and this looks like it may be the problem -tell me what you think ... Rear 0 degrees, driveshaft 2 degees, trans 15 degrees and the APP says that I'm not in specs.

    So, I have never fixed anything like this, but everything I have found, indicates that I should target 3 degrees front, 3 degrees rear -with them in opposite directions but parallel.
    Am I understanding this right?
    If so, the trans is negative 15 degrees -so I need to bring it up with shims or??? to get to -3 degrees
    Then try to raise the rear at the pinion to get to + 3 degrees -how do I adjust this?
     
  4. Jodi

    Jodi Veteran Member

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    Collapsed Engine/Transmission mount?
     
  5. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    15*? That can't be right or the mount is broken or wrong.
     
  6. G72Zed

    G72Zed Veteran Member

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    A 15* downward engine trans angle is out to lunch, how did you measure the trans angle, or more importantly, what surface did you use? something is not right. A 15* angle will induce carb issues to a point.

    And you do not want to setup a leaf car with equal and opposite angles at rest, if so, you will have + pinion angle at speed due to axle wrap, and get's worse when you "getting on it".
     
  7. Glava

    Glava Veteran Member Lifetime Gold Member

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    Oops its 5 degrees not 15 degrees -sorry. I put a straight edge across the tranny output at the seal.
    So what would you recommend that I try at this point?
     
  8. Bandit723

    Bandit723 Veteran Member

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    I would go for 2.5 degrees at the tranny or engine to start. some shims may help but i suspect the setup is leaning back to far.
     
  9. checkmate201

    checkmate201 1970 SS 350 4sp 06 C

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    MChamp likes this.
  10. COPO

    COPO Veteran Member Lifetime Gold Member

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    I don’t believe the factory created this problem and couldn’t fix it under warranty. I ordered new 4 speed Z28’s in 77, 78 and 80 and never had a vibration. Maybe I was lucky but I dought it.
     

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