front-end shimmy/hop - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-26-1999, 07:16 PM
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front-end shimmy/hop

Hello list,
I just installed a 4" Trailmaster suspension lift and 33X12.5 BFG A/T's on
15X10 wheels on my 90 Full-size Bronco. When I hit some bumps going about
30-40mph I get a violent shimmy and hop in the front. I then have to slow
down and regain momentum. The entire front-end seems to be tight and I have
new ball joints, a dropped pitman arm, new shocks, and a stabilizer. Is there something else that can be causing this and what damage can this be doing to my truck?
Could it be in the steering box, caster, driveline, lack of bumpstop
extensions, etc? The truck also has a tendency to pull to the left.

Any help would be greatly appreciated.

Thank you.


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post #2 of (permalink) Old 09-27-1999, 12:28 AM
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Re: front-end shimmy/hop

Check your bearings and steering components, there is some play somewhere up front. When you start the loose component is stationary but when you hit a bump it shifts that component and causes the shimmy and hop.

post #3 of (permalink) Old 09-27-1999, 09:15 AM
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Re: front-end shimmy/hop

I agree with Bravoman, something's probably loose. Won't take much, especially with the wide rubber you've got! I don't have experience w/lifts, but troubleshot a violent front end Bronco shake. Would only occur on a sweeping right-hand turn between 40-45 MPH if a bump was hit. Was real bad, like the whole thing about to come apart. Slowing to about 30 would cause it to dampen out. When it was shaking, speeding up would not make it stop, but it would shake at the same rate (not any faster, even though ground speed was faster). It seemed to be oscillating at some resonant frequency. But clicking on 4HI would dampen it out. Found that the nut & bolt through the hinge bushing (where the traction beam axle pivots up and down at) for the right axle was just hand-tight. They're supposed to be torqued quite a bit. That was it - somebody had the axle apart, probably lined it up and put the bolt and nut on, and forgot to go back and tighten it properly. Since it didn't pinch the bushing and bracket hard enough, it allowed a little play under road load, which allowed it to steer that beam and wheel a little bit. The radius arm stops front-to-back play in the axle, but won't stop a twisting effect of the beam's hinge point moving around. That's all it took, in the right conditions the whole right beam and axle assembly would oscillate. Clicking 4HI "ON" would make that wheel pull, which probably held the free play to one side. So check real closely! Hope this helps, UncleDon.

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