vibration after 2 inch shackle install on 2010 Silverado Crew - help

Discussion in 'Lifted & Offroad Suspension' started by kalashluvr, Oct 14, 2010.

  1. kalashluvr

    kalashluvr Rockstar

    hi, just wondering if anyone can help.

    had 2 inch shackles installed on 2010 Crew yesterday, now I have a mild vibration from about 25-32 mph.

    The shackles were tightened with the truck rear sitting on the ground and not jacked up.

    Any ideas?
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    A 2" inch change is a minor amount & shouldn't have caused vibration on a 2010 as everything is new, but my guess would be the change in drive shaft angle is causing this. More angle causes extra pressure on the u-joints. Maybe the factory forgot to grease one??
    The easiest way to check if the 2" height increase caused this, is to throw enough weight in the back to bring it back down to stock height and go drive it.

    ** It is proper to tighten shackles with static weight down on the springs/shackles so no problem there.
  3. kalashluvr

    kalashluvr Rockstar

    It was actually a 2 inch drop....which would be the equivalent of hauling about 350 lbs in my estimation (a couple of guys stood on my bumper to give me an idea what it would look like when leveled, and it was exactly 2 inches.).

    I actually loosened all 4 bolts last night, hopped up and down on the bumper and heard some settling, then re-torqued the bolts to 70 lb/ft. Vibration is still there as of this morning.

    I'm sure I would have noticed this vibration before the shackles were installed, but now I'm second guessing myself...I noticed it immediately after the installation though. Ideas will be appreciated.
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    OK, I thought the 2" was 2" over stock. 2" drop would decrease d.s. & u-joint angle. Still since the vibration started after you did this, it seems like it has to be the cause. Did you make any other changes recently, tires/wheels/have a flat & put the spare on? Put a hot tub in the back?:great:

    What does it feel like at 55-65 mph?
  5. kalashluvr

    kalashluvr Rockstar

    To All:

    2 degree pinion shim fixed the vibration. Part number is 4975 from Belltech.
  6. stephan

    stephan Rockstar 4 Years 5000 Posts

    Thanks for the update Kalashluvr. It's always nice to hear what the final results are.
    This is troubling though because as you said, the 2 inch shackles were equivalent to adding about 350 lbs to the bed of your truck as far as lowering it. Since this is the case it seems that if you were to haul 350 to 400 lbs in it now, the vibration would come back. Same as if you had never put the 2" shackles on it in the first place, & had just put the extra weight in it at that time. I think there's something else going on here. Any thoughts?
  7. kalashluvr

    kalashluvr Rockstar

    Actually, after thinking about things, and looking at what the shackles do, the shackles are not equivalent to putting a load in the bed. With factory shackles, and a 350 lb load, the pinion angle never should change much because the springs are staying even as the weight pulls the bed down, and even if a load DOES change the angle, it should probably tip it slightly upward rather than down. The drop shackles on the other hand, actually push the back of the spring up 3 inches higher, and EVEN THOUGH the bed is lowering, the rear spring hanger is changing in relation to the front, and tilts the pinion/rear forward.

    Just imagine the weight being placed in the bed or attached to the bumper....the springs are even on the front and back, and absorb the weight and move up and down. Push the rear of the spring up with the drop shackles.

    As far as lowering the rear of the trucks, I think that simply removing the blocks (between the mount pad on the top of the axle and the bottom of the spring), the pinion angle won't change. Removing the blocks might not drop the rear of the truck enough for some folks though.

    (a side note....if you look up a rear shackle kit for a 2006 F-150 on Jeg's website, the shackle kit actually comes with shims.)
  8. stephan

    stephan Rockstar 4 Years 5000 Posts

    Good explaination. I never have put shorter or longer shackles on any of my rigs. I did take the 3rd leaf out at one time to level the truck which is as you describe, and imparts the same angle because it was not lowering the front or rear spring eye but rather the truck as a whole. Doesn't this shim you put in end up changing the front u-joint angle also? Why does this not create another problem in the front?
  9. kalashluvr

    kalashluvr Rockstar

    The shim in the rear looks like a very thinly sliced pie turned on it's side. Just imagine cutting a circle into 180 pieces of pie, 2 degrees each. That's what the shim looks like. And when you insert it between the block and spring, then tighten the u-bolts back up, the thin leading edge and fatter rear (fat edge goes toward rear if the axle is on the bottom of the spring) rotates the pinion back to where it was originally. So if the front angle was changed very slightly also when the shackle was installed, it is back to normal matching angles after the rear shim is installed.
  10. stephan

    stephan Rockstar 4 Years 5000 Posts

    Yep, I know what the shims look like & how they work, it just seems like the shim would affect the front u-joint angle "for the worse" & inadvertently cause the problem to move there.

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