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  1. #1

    Default 1990 Suburban engine vibration?

    Hey guys, I'm new here and I have a question for y'all:

    I have a 1990 Suburban with the fuel-injected 350. In gear or not, when it hits about 2,500 RPM, the whole truck will start shaking, and that lasts till about 3,400 RPM when it for the most part goes away. My question is, what could be causing this? It does it in park/neutral and when I'm driving, so I know it's not a drive-train issue.

    I've heard several different things that could be causing this, from the harmonic balancer to the fan clutch. I'd like to get this figured out as it really bugs me.

    Any ideas?
    Last edited by bigburb; 01-26-2009 at 09:54 PM.
    Current truck: 1996 Ford 250, 7.3 Powerstroke diesel. Dana 60 SAS, stage 1 160cc injectors, T500 High Pressure Oil Pump, TS 6-position chip, full 4" exhaust, intake, 285 Falken Rocky Mountain AT's, boost/EGT/trans temp pillar gauges, etc...

  2. #2

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    Broken motor mount?? Its easy to check anyway.
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  3. #3


    Yeah I've considered that too. I'm going to go through all the motor and tranny mounts tomorrow now that the school week is over. It idles and drives smooth below those RPMS, so I really don't know what to think...

  4. #4
    Legend tlperry68's Avatar
    Join Date
    Oct 2008
    Huntington Beach, CA


    Yep, harmonic balancer (was the tranny ever changed from a manual to an auto?), broken mount, wrong engine fan. There could be any number of things. Maybe even the oil in your torque converter turned to sludge.
    Trevor - Huntington Beach, CA
    2007 GMC 2500 4X4

  5. #5


    As far as I know, the engine and tranny are completely stock. No re-builds or anything. I was talking to my dad about the harmonic balancer and he just didn't see any way it could go bad, considering it's basically just a big piece of steel.

  6. #6


    The balancer is actually two pieces of steel. An inner ring and an outer ring with rubber between them. If the rubber has started going bad, the two rings can start to separate.

    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

  7. #7


    So do you think that would most likely be the problem?

  8. #8
    Sr. Apprentice
    Join Date
    Dec 2008


    Usually the balancer will only go bad when someone has either tried to remove it with a hammer or a two or three jawed puller as this will separate the rubber from between the two pieces of steel

  9. #9


    I don't think it would be the balancer either. Could just be a misfire. Have you done a tune up recently?

  10. #10


    Well as far as I know the balancer has never been removed. But, I've only owned it since April of '07 and it's almost a 20-year vehicle so who knows.

    And no, I haven't done a tune-up at all in the 2 years I've owned it, and I don't know when the last one was. Could a mis-fire cause these symptoms? It run's and drive smooth below those RPM levels and doesn't appear to have a lack of power.

    EDIT: Well, last night I put in new Bosch Platinum Plus spark plugs, a new Duralast Gold Series cap and rotor set, and a new set of Duralast plug wires. It seems to have helped reduce the vibration a little bit, but it's still there.

    Any other suggestions?
    Last edited by bigburb; 01-28-2009 at 02:39 PM.

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