1973 RS LT Z28- chasing a vibration above 40 MPH

Discussion in 'Troubleshooting & Diagnosis' started by Lou6t4gto, Dec 2, 2017.

  1. Lou6t4gto

    Lou6t4gto Veteran Member

    Aug 18, 2010
    Ocala, Fla
    over the past 10 years I've been afraid to drive the car on the "interstate" ! it has a 350+.030, 350 300hp cam,Q-jet, idles smooth at 500RPM. new engine mounts, trans mount. stock converter, 2.73 gears. The car picks up a "vibration /shake" above 40 mpg. All of front suspension is new, All of rear suspension is new, new tires(235x60) on stock (straight 15x7) wheels. It Does Not seem to be RPM related. I can get up to 70 MPH, put it in neutral, and the shake is still present ! I think I also replaced the driveshaft with different "used" driveshafts over the years. Any Help would be GREATLY Appreciated. I want to drive my car .LOL
    Thank You
  2. tom3

    tom3 Veteran Member

    Aug 1, 1999
    Pretty much eliminated anything in front of the transmission, pretty slow for a tire shake. With the 2.73 gears that's pretty slow for a driveshaft too unless it's really screwed. I'd get the back wheels off the ground, remove tires and drums, spin it up and see if the vibration is there. Look at the driveshaft for runout, not centered or bent.
  3. Lou6t4gto

    Lou6t4gto Veteran Member

    Aug 18, 2010
    Ocala, Fla
    anything else to check ? thanks
  4. Z28zz383

    Z28zz383 Veteran Member

    May 11, 2012
    Find another set of tires and wheels from any thing that will bolt on it and try that. I found that I had a bad stock cast n-90 wheel that would vibrate over 50. Faster you went the worse it got. Blamed it on the tires/balance job for years till I got some new tires balanced on a road force machine. It showed a wheel was bad. Slight runout problem if I recall correctly.
  5. z28will

    z28will New Member

    I'd go with a wheel re-balance and make sure the tire shop balances the wheel by the bolt holes and not the center hole of the wheel. I got rid of a serious vibration that way.
  6. hoppin5478

    hoppin5478 Veteran Member Lifetime Gold Member

    Jul 20, 2015
    Tucson, AZ
    If the vibration is more in the front or rear, left/right, you can try rotating the tires and see if it moves to narrow it down to a tire/wheel issue. Over the years I have seen new wheels manufacrured poorly and cause a vibration, we even exchanged the wheel several times before we could get a decent one, tire issues where the tire was oblong and not super obvious, flat spots etc. If its speed dependent, gets worse the higher the speed and doesnt change with rpm ( as you indicated) or transmission shifting its going to be driveshaft back in the rear or wheel bearing out in the front. Id look for bent driveshaft, axle, bad/ loose bearing, tire/wheel issue. I hope you find it so you can enjoy it.
  7. Crazy4camaro

    Crazy4camaro Veteran Member

    Dec 30, 2015
    Greenville SC
    Have you put the rear up on jack stands and tried it?
  8. rocket dawg

    rocket dawg Veteran Member

    May 5, 2015
    Grand Rapids Mi
    I battled a vibration for years on mine as well. Rebalanced the tires, nothing-driveshaft balanced= nothing. Vibrating came in around 50 mph and got worse. I finally put new tires on it and that was it. one of the tires or more was bad even though they balanced out right multiple times. Not sure if it was tread separation or broken cords inside.. Tires were old but 75% of the tread left. Jack up the car and look for a wobble on the wheels or oblong out of round tires.
  9. ssupercoolss

    ssupercoolss Veteran Member

    Nov 3, 2015
    I had the same issue on a Tacoma i had. Everything would balance out fine. the hood would shake at 40 plus. Swapped the wheels and tires from my 4runner to find the tacoma had a bad rim.
  10. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

    Mar 24, 2001
    Rockledge, Florida
    I have the same issue. I have an M21 with 3:73 gearing. I did a lot of looking but I suspect I have too much slop in the ring/pinion gear area. My guess is there is a constant fight between the gears meshing at high speed...kinda like pressing and releasing the gas pedal very quickly.

    Here is a video we made at the PAFB auto hobby shop of the play:

    Here is a pic of the inside where someone pounded the crap outta the retaining pin. This may have effed up the rear end. I really need to find a rear axle specialist and go take a look.


    By the way, do you have stock rear brakes?

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