Cyclical Vibration

Discussion in 'Small Block Tech' started by DeeVeeEight, Aug 3, 2016.

  1. DeeVeeEight

    DeeVeeEight Well-Known Member

    At rpm's over 2200 or 2300 my 350 4 bbl starts to generate a cyclical vibration that seems to travel through the length of the car, then it subsides and then it starts all over again. If I keep my road speed under 60 mph I do not experience the vibration. It will do it in park too, over 2200 - 2300 rpm it starts to vibrate.
    Could this be old motor and trans mounts or something else?
    Other than this drive train vibration the car rides smooth as glass.
     
  2. gstewart

    gstewart Well-Known Member

    possibilities-
    cooling fan out of balance or bent, engine out of balance, torque converter out of balance, flexplate out of balance or cracked
     
  3. sean Buick 76

    sean Buick 76 Buick Nut

    Most likely a harmonic balancer that is falling apart.
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Could also be exhaust system resonance/harmonics. Does it sound like the engine is surging, but it isn't? Did it start after your exhaust system installation?
     
    Mark Demko likes this.
  5. DeeVeeEight

    DeeVeeEight Well-Known Member


    No the vibration existed before the new exhaust system.. The harmonic balancer has not slipped yet, it was checked recently. The fan is easy enough to take a look at. I have had several get loose over the years and make weird noises and vibrations. As for the converter and flex plate, those will have to wait for the trans rebuild some day.... and if the engine were out of balance, wouldn't it be noticeable at all speeds?
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If you can recreate the vibration in Park/Neutral, then it is in the engine, or torque converter. One thing you can try is unbolt the torque converter, turn it 1/3 of a turn, and bolt it back up.
     
  7. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    I have heard the cyclical vibration was one of the variance features of the rheostat implemented on the oscillatory orifice palpitation facilitators, but that's just rumor.
     
  8. jay3000

    jay3000 RIP 1-16-21

    It's the Binswanger effect caused by a mis-alignment of the universe. Gary's drinking already:laugh:
     
  9. sean Buick 76

    sean Buick 76 Buick Nut

    Did the vibration start all of a sudden or did it always do this?
     
  10. Mark Demko

    Mark Demko Well-Known Member

    Do you have a flex fan?
    Flex fans are garbage.
    Disconnect all the belts and run the engine, then do the same with the torque convertor, remove the 3 bolts, and run it.
     
  11. DeeVeeEight

    DeeVeeEight Well-Known Member


    It's a stock clutch fan. I was under the hood yesterday checking for water pump shaft and fan shaft play but could not find anything significant. I'll have to try your suggestions.

    Sean - it's been doing this for as long as I have had the car.
     
  12. sean Buick 76

    sean Buick 76 Buick Nut

    Could easily be the flexplate not bolted up in the right orientation. The flexplate is weighted to balance the engine out externally. If bolted up wrong it would vibrate.
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I don't think that is possible Sean, the bolt spacing is such that it only goes on one way.
     
  14. jay3000

    jay3000 RIP 1-16-21


    YES.. Only goes one way.
     
  15. budbrown

    budbrown Member

    I'm having the same issue on my 72' 350. Did you ever figure out what the issue was?
     
  16. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    This tells you that it has something to do with the engine's RPM, not the speed of the car, so that rules out other drivetrain components.

    If it is cyclical, (not a steady hum or frequency), indicates something with frequency resonance fluctuations within that specific spectrum of RPM range, which could indicate the exhaust has something to do with it.

    Some things to check would include motor mounts (and transmission mount), their position and relation to the engine/frame pads (transmission crossmemeber) or frame, or anything that could be in close proximity to them, including exhaust components; the exhaust itself and how close anything is to it (check mounts, clearances, etc.); check mufflers too (is this interior drone?) Does your exhaust turn down at the mufflers or does it have tailpipes? Check transmission lines and anything they could be vibrating up against too.

    Check other engine components to make sure there's nothing loose. Check torque converter (and flexplate) while engine is running to see if there's any wobble in it.

    Maybe have a friend hold the gas to the RPM where it makes the sound, and crawl around to listen/look for anything noticeable, or at least isolate the area where the sound is coming from.

    Did I forget anything?
     
  17. DeeVeeEight

    DeeVeeEight Well-Known Member

    UPDATE
    I got rid of the Cragar rims and staggered size tires. I replaced them with aluminum 15 x 7 Scott Drake Magnum 500's (they look a lot like Buick Sport wheels) and Cooper whitewall tires. I also had the brakes gone over at a local shop. Cyclical vibrations are reduced if not gone. I need to spend more windshield time for 100% satisfaction before I say it's fully cured.
     
    TrunkMonkey likes this.
  18. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    How about the center caps? Picture?
     
  19. TrunkMonkey

    TrunkMonkey Well-Known Member

    I had that problem once a long time ago. Changed radio stations. It was the Beachboys. But I kept the girl...
     
    Max Damage likes this.

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