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Violent Shimmy at 40-45 MPH

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by klier, Jun 19, 2000.

  1. klier

    klier Registered Member

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    Hi Everyone!

    I am new to the forum. I have a Project '86 K5 Blazer 4x4, which is actually sitting on a '74 GMC Jimmy Frame, and has a pickup truck bed welded to the back instead of the enclosed cab. I just recently purchased it, and it has been sitting for quite sometime, so it is in the process of being restored/tuned up.

    The problem I am having is that at around 40-45 MPH, all of a sudden the vehicle will violently shake. I mean VIOLENTLY shake. The steering wheel will jump to the left and right, the transfer case shifter will be thrown left and right. The violent shimmying will continue until the vehicle is slowed to around 10 MPH, and then it will be fine until it reaches about 40-45 MPH again. Almost seems like there is a point that the chassis starts resonating and almost seems to steer on its own... This shaking is so severe that the first time it happened I just about loaded my pants. It felt like the frame was being twisted apart.

    The drivetrain is stock - a Chevy SB 350 was dropped in there quite a while ago, so there is no computer stuff to worry about. The vehicle runs fine at 30 MPH around town.

    Here is some more help: I was able to drive it at 55 MPH for about 8 miles this weekend. I checked the air in the tires, and all the tires were low, but the two right-side tires had about 15 PSI in them. I aired up both passenger side tires to 35 PSI. This is the only thing that I remember doing before I started having this problem.

    My thoughts? Maybe flat-spotted tires, Steering Stabilizer, Wheel Balance? Otherwise, I am at a loss. I am hoping someone else had a similar problem that was solved that could pass on the information to me.

    Thanks for any help you guys have!

    Brian Klier
    Faribault, MN
    brian@kliernetwork.net

    My Project Blazer Website: http://kliernetwork.net/truckproject

    [​IMG]
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Have an alignment shop check the caster angle. Sounds like yours is at, or near, 0 degrees. That will make your tires behave like one of those shopping carts that vibrates a wheel like crazy.

    Loose parts will make it worse. Ball joints, steering parts, etc. will all exacerbate a caster angle problem. I think the spec is 3-5 degrees of positive caster but the alignment shop will have the specs in their books.

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     
  3. Mikee

    Mikee 1/2 ton status

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    Yep, I had that problem in my '85 GMC3500 plow truck. Found it to be a cracked frem behind the steering box, and the stabalizer, actually I think the whole problem was the stabalizer, and it just cracked the frame. I'd check all tire rods, ball joints, replace the stabalizer, and look for cracks around the bolt holes of the steering box. repair/reinfocer plates are available from just about any off road place (common problem). Then get it aligned. You'll be all set, I spent $2000 trying to figure it out. Go with the stabalizer first, just a hunch.

    "Got stuck once, hung up on top of a Jeep!"
     
  4. coopertwpk

    coopertwpk 1/2 ton status

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    mine did this it was the ball joints a buddy leaned out the window and could see the tire shake
     
  5. Blazer79

    Blazer79 1/2 ton status

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    I'd recommend you balance all tires first. That's cheap and you will easily tell if a wheel is bent. That's what was happening to my 2wd Toyota truck after hitting a deep hole in the pavement. The steering wheel was shaking violently by itself after getting some speed.

    I had to replace the bent wheel. Fortunately I have the cheapest wheels you can find on that truck ($15/each!). Also check if all the lugs are there and properly torqued.

    Hope this helps.

    PS Nice website.

    <font color=blue>//////
    http://blazer79.coloradok5.com
    </font color=blue>[​IMG]
     
  6. klier

    klier Registered Member

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    Thanks everyone for their suggestions. Hopefully, as I get more work done on the Blazer, I'll be able to answer some questions down the road for some of you guys.

    Glad to be a part of the forum!

    Brian
     
  7. klier

    klier Registered Member

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    Re: Violent Shimmy at 40-45 MPH (SOLVED)

    Hey Guys...

    The alignment shop put a new steering stabilizer in (the old one had no shock action at all - and seemed to stick in a few places as it was pushed in and out), also the wheels were balanced. Toe In was also adjusted. These few things solved my violent shimmy at 40-45 MPH.

    Just figured I'd post this so if anyone else has a similar problem in the future, that these are some of the cheaper things to try.

    Thanks for everyone's help!

    Brian Klier
    Faribault, MN
    brian@kliernetwork.net
     

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