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  1. #1

    Default Help!! 98 Chevy Z71 Vibrates Violently at 40-70mph... Thinking TCC or fluid pressure?

    I'm new here and have searched everywhere, but cannot find a solution to my problem, so please forgive me if I've missed something in the search engine.
    I have a 1998 Chevy 1500 4x4 ext. cab truck that just started this problem:

    Problem:


    In the beginning I noticed when the vehicle is at normal operating temperature, and has been driven around 10+ miles, going from 40-50mph the whole truck would shutter &/or vibrate Violently at about 25% throttle. This problem progressed as the days went by and now it’s doing the same thing but at speeds of35-75mph. If I let off of the throttle, or give it more throttle the vibration quits, but returning back to normal throttle operation of about 25% it returns to vibrating severely.


    What I Have Tried:


    I have had it scanned and no codes appear.


    I do know that the brake or BOO switch has some control over the TCC (I think this is correct but not 100% sure) So today while test driving it I noticed when it starts to vibrate if I press the brake pedal it quits. Once I release the brake it returns to vibrating, but if I hold the brake down a little bit and continue to throttle there is no vibration.


    My question is:

    Do I need a new Transmission valve body, a new torque converter, new transmission, or is there a control module that is known to go bad? Maybe just a simple fluid/filter change?

    I could be wrong, but since the brake switch does allow the lock up to stop and torque converter to slip when I press the brake, so I assume it is working properly and doesn’t need to be replaced. If I'm wrong that would make my New Year!

    Solutions:?????


    Any and all suggestions would be greatly appreciated!! Thank you so much for you time!


    P.S. I was thinking of going to the local u-pull-it and pulling a valve body to try and correct the problem, is this a waste of time and money throwing a used $45 valve body on it?



    Last edited by SaNe; 01-01-2012 at 06:15 AM. Reason: errors

  2. #2

    Default

    You have a bad rear universal joint. Because it is bad there is slop in your driveline. The reason you feel it at those higher speeds is because at slower speeds it is not spinning fast enough to cause that harmonic vibration that you are experiencing. Also the reason you only feel it upon being under acceleration.

    The part is very inexpensive, probably $20-$30 dollars. It should be in stock at any autoparts store, Advance, AutoZone, Pep Boys, Napa, etc. If you can't change it out yourself, a shop will probably charge you an hour worth of labor to do it.
    -2001 Suburban 2500 LT 8.1
    -2000 Silverado 1500 LT Z71

    Gone but not forgotten:
    -2007 TrailBlazer SS
    -2004 Cadillac CTS-V
    -1998 Silverado 1500 LT Z71
    -1989 Pontiac Formula WS6

  3. #3

    Default

    Thanks for the response Corso.
    I have checked the u-joints, driveshaft, pinion and bearing, and the transfercase shaft splines. Everything from the transfercase back was fine.
    There is hardly any play and zero noise in the driveline whatsoever, but does that mean that I could still have a u-joint bad?

    Also I can continue to accelerate with the brake pedal lightly pressed down and the vibration goes away completely, so long as the brake is held down. As soon as I release the pedal it continues to vibrate again.


    Also this barely holding the brake pedal down while accelerating stopping the vibration and that I only get the vibe at 25% throttle is what makes me think torque converter.

    Quote Originally Posted by Corso View Post
    You have a bad rear universal joint. Because it is bad there is slop in your driveline. The reason you feel it at those higher speeds is because at slower speeds it is not spinning fast enough to cause that harmonic vibration that you are experiencing. Also the reason you only feel it upon being under acceleration.

    The part is very inexpensive, probably $20-$30 dollars. It should be in stock at any autoparts store, Advance, AutoZone, Pep Boys, Napa, etc. If you can't change it out yourself, a shop will probably charge you an hour worth of labor to do it.

  4. #4

    Default

    Hmmm, not to sure then? Sure sounds like a u-joint. Are you sure it's not something as simple as a wheel out of balance?
    -2001 Suburban 2500 LT 8.1
    -2000 Silverado 1500 LT Z71

    Gone but not forgotten:
    -2007 TrailBlazer SS
    -2004 Cadillac CTS-V
    -1998 Silverado 1500 LT Z71
    -1989 Pontiac Formula WS6

  5. #5

    Default

    Yea, just had the entire front end replaced less than 2,000 miles ago, and already had them check everything including alignment and balance all tires just for this reason... Firestone is just clueless as to what it is.

  6. #6

    Default

    Just a reminder, this only happens after the truck has warmed up and has been driven about 10-20 miles before it starts shuttering. When it's cold it runs great. That's another reason I think the problem is in the tranny...

    Any ideas?

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