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strange vibration/ sound PLEASE HELP

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Cornfed-90K5, Feb 21, 2001.

  1. Cornfed-90K5

    Cornfed-90K5 Registered Member

    Feb 17, 2000
    Likes Received:
    Fresno, California
    I have a six inch lift on my blazer and have been having problems with curing the driveshaft vibration. If I drop my t-case low enough to get rid of the driveshaft vibration, I get a wierd sound when I back-up. This is usually either when I back-up under a load (up hill) or if I accelerate (anything more than idle), it will also do it if I put my foot on the brake and lightly give it gas while in reverse. It sounds like something is binding, but I don't know what it could be. My t-case is dropped about 1 1/2". I have played around with many different amounts of drop, and I either have driveline vibration or this other thing. Please help I am getting really frustrated.

    1990 K5 Blazer
    TBI 350, 4L60-E, NV241,
    6" lift, 35" Pro Comp M/T,
    4.56's and Auburns front and rear
  2. yeild2me

    yeild2me 1/2 ton status

    Jan 7, 2001
    Likes Received:
    fayetteville, nc
    mine started doinfg the exact same thing after i dropped my t-case....my drive way is 20 feet but with a slight rise to the street, when i back out it does it, but then again it also does any other time, just not as bad......the angle is excellent, so i dont know what it is.....let me know if you figure something out, and ill do the same..........

  3. ftn96

    ftn96 1/2 ton status

    Sep 26, 2000
    Likes Received:
    Nashville Tn
    Have you guys checked your transmission mount? When you lower your t-case it puts a little more load on your transmission and engine mounts. Check those first. Next I would say that maybe you have a bad u-joint somehwere. Maybe on the front D-shaft. As you drop the t-case it puts the front driveshaft more in a bind thus if you have a u-joint on its way out it would be more noticable now. Check these things and post back.
    One more note, you may or may not know this. But when in drive the driverside of the engine will tend to twist up out of the truck, and in reverse the passenger side will twist up. If one of those mounts is bad you'll get some clunking of some sort. Also when you hold on the brake and gas it you will find these noises to be more noticeable.

    Will work for beer, parts and tools.
    90 Jimi,350/700R4/241/10bolts/4.10's/33's/4"
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A><P ID="edit"><FONT SIZE=-1>Edited by ftn96 on 02/22/01 07:50 AM (server time).</FONT></P>
  4. DPI

    DPI 1/2 ton status

    Jun 22, 2000
    Likes Received:
    In the Burbs close to Tulsa, OK
    I have about 8" in the rear and mine does the same thing when I dropped my case. I think it is coming from the motor mounts binding up and you are feeling the vibration from the motor. I lifted my case back to the original position and installed a CV rear shaft. I am going to go with the slip yoke eliminator on my 241 or go with a 205 with a fixed yoke, haven't made up my mind yet.
    Here is my CV I installed.
    <IMG SRC="http://albums.photopoint.com/j/View?u=1439605&a=10797147&p=37538560&Sequence=0[/image]


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