beam shake

Discussion in 'Lifted & Offroad Suspension' started by steingang2, Jul 18, 2008.

  1. steingang2

    steingang2 New Member

    my 06 crew cab 1500 silverado has what the dealer calls "beam shake". The frame is made of a lighter weight material and causes the rear end to vibrate when decelerating between 60-40 mph. They say it is not a safety issue so they did not want to fix it, although they have been aware of the problem for years. they recommended putting 300-500 pounds of weight between the tailgate and the wheelwell to reduce the vibration. why have a bed if you have it filled with concrete blocks all the time. After waiting 2 years for a fix, the dealership is going to put a newly modified body mount on. I don't know what the difference could be. My idea, if this does not work, is to put a leveling kit on the front to put more weight on the rear end to dampen the vibration. Anyone else tried to solve this beam shake?
  2. zippy

    zippy Rockstar 100 Posts

    There's a whole lotta shakin' goin' on....

    You're not alone in your complaint. Just google "beam shake" and you'll get a boat load of hits. It seems to be an inherent problem resulting from GM's attempt to lighten the frame. Yes, the service bulletin recommends adding weight between the tale gate and the axle in diagnosing the problem.
    Some folks say the problem can also be reduced by changing the OF tires, others recommend changing U-Joints.
    Adding concrete blocks for additional weight seems to defeat the purpose of lightening the truck for better economy. If you're going to add any weight, perhaps it should be structural where it can earn its keep.
    When you talk to the old school boys about the shakes, a modification comes to mind that may cure your problem: Provide a center joint in your drive shaft. This may involve adding a cross member to your frame. You didn't mention if your truck is 2x4 or 4x4.
    I don't know if your truck is a candidate for drive shaft work, and your dealership is not going to admit that GM should have provided one (assuming you don't already). The last time I had drive shaft work done at an independent specialty shop, the rear parking area was full of new Ford crew cabs waiting to be converted. They had dealer installed rims and big tires. Apparently, they couldn't go over 60mph without shaking before the shaft upgrade.
    Before you start any alterations, perhaps you should get an opinion other than your dealership's. You didn't mention your location, but there's probably a independent specialty shop in your area.
  3. steingang2

    steingang2 New Member

    The best way to describe this vibration is it feels like the rotors are badly warped, only they only vibrate at certain speeds and under certain conditions, like decelerting between 55-down to 40, then it stops. The rotors, shocks and tires have all been checked. The new and improved body ounts get installed tomorrow, then we will see what difference it makes.
  4. zippy

    zippy Rockstar 100 Posts

    Keep us posted with the results. What does your dealer recommend next, an exorcism?
  5. steingang2

    steingang2 New Member

    Well I dropped the truck off at the dealer this morning and got a call 2 hours later......they forgot to order the new body mounts! They did give me a copy of the revised bulletin and it says to install the new body mounts under the rear of the cab so it must just dampen the vibration and not eliminate the problem from occurring in the first place. From talking to ohers it seems this problem is caused by a "C" shaped beam instead of the old "I" beam or boxed beam used in heavy duty trucks. The "C" portion of the beam vibrates at certain speeds. I will wait until it is put on before I decide to put the leveling kit on.
  6. ridleyredraider

    ridleyredraider New Member

    I just got a 2010 Ext Cab, put 2" lowering rear shackles on the rear leaf springs. I've torqued the bolts a few different amounts, but every time the truck downshifts (and this damn thing has 6 gears) as I'm rolling to a stop light or whatever, the rear end shakes from the transmission down-shifting.

    1. Is this because I still haven't torqued them correctly/too loose? I have them at 30ftlbs right now, I was told somewhere between 25-35 is best.

    2. Is it because the geometry of the leaf springs (rear leaf spring is 2" higher) is getting a translation movement (back and forth instead of up and down) and they're vibrating when the downshift occurs?

    3. Is it because the rear end is now 2" lower, so the shocks are sitting 2" into the stroke, giving too much rebound or feedback to the bed and frame?

    I guess for now I'll try a higher torque, which may help, but may squeak, cause binding, and make for a stiff ride.
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Your problem sounds more like a combination of lower leaf spring geometry and the shocks bottoming out.
    For the shocks you can unbolt the shock then lift the rear and measure the distance between the shock mounts when the spring's stretched out then compress the rear spring and measure when the springs compressed. Contact a good shock manufacturer and they should be able to tell you the correct size required.
    The spring geometry wont be as easy unless you want to lose the 2".
  8. xmech

    xmech New Member

    Sure sounds familiar, back in the 70's there was the same problem with the C10 2wd. there was a recall on installing counter weights at the very rear of the frame. I think they were aprox. 25lbs. each one on each side.

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