I see that Stellantis is finally settling over the Jeep death wobble..

[5030]

The more joints, the more slop, the more wobble.

 

[2LaneCruzer]

Older cars had what they call king pins (before ball joints) that would cause wobble when worn. My old 1930 Chevy would sometimes dance all over the highway. Of course, it was never driven fast at all.

 

[zzvyb6]

Here's THE explanation of this form of what has been called 'shimmy' long before many of you were born. Keep in mind, I have over 40 years of automotive engineering in the Vehicle Dynamics realm, and have even worked on hybrid specialty vehicles (limosines) that you might see on TV in National News reports that needed this problem addressed.

'Shimmy' is the unintended result of coupling between vertical wheel movement and wheel steer movement (not steering wheel movement). The root cause is non-zero angle on the single or double tierod(s) connecting the Pitman arm to the tie rod connection(s). If the tierods are not horizontal in the front view, your front suspension is susceptible to shimmy. A vertical wheel displacement (bump or pothole or tire imbalance) excites lateral forces in the steered wheels mechanism. Much like an inverted pendulum, the oscillation grows because of positive feedback from the steer mode to the vertical mode of wheel travel. Like any pendulum system (hinged from the top or bottom, techniques to reduce or eliminate it involved damping from either friction (new suspension parts) or dampers (steering shock absorbers), or removal of the coupling factor. Obviously lift kits that do not re-align the Pitman arm are principle players. 'Bulldozed' springs which lower the body also are involved. Bulldozed springs are deformed (as in bent) usually from overloading due to many situations. This aggravates the coupling term. Additionally, vehicles with power steering can have worse shimmy because the flow valve in the steering gear will respond to the increased tierod loads in an attempt to reduce them, but with a phase delay that actually increases the forces. Worn steering system parts (lower friction), worn-out pump, lower rack&pinion slipper bearing friction, valve leakage, play in ball joints all add up to create the shimmy phenomenon.

Tires are also players because the air pressure, tread width, wheel rim width and sidewall stiffness of the tire carcass affect the steered stiffness of the tire (called self-aligning torque stiffness). So tire brand, wheels and pressure are ways to reduce the problem or make it worse. Sure, steer dampers help to reduce the amplitude of the shimmy, but eventually these parts wear out or get damaged from the high forces and soon the problem returns. But the root cause is the positive feedback in the steering mechanism.

Note that many of these trucks have symmetric ride steer. (both wheel turn the same way when the front end rises. In most vehicles with purely independent suspensions, the wheels turn in opposite directions when you raise the front end up. (called ride-toe or bump steer). This parallel steering design also feeds the problem because both tires scrub the same way instead of one tire cancelling out the other's steering resistance moment. Note that many different Pitman arm drop dimensions are available from truck specialty shops which correct the geometry factor of this problem. Steering gear stays put, steer arm ball height is altered as installed. But the loss of friction from wear/mileage is always going to aggravate the situation. Plus, soft springs means lots of wheel travel, so the Pitman arm can't always be horizontal.

Now you know the reason(s), many science projects and technical papers written about the subject, but the lore from owners with 'feelings' instead of facts & data permeates the web.

 

[Rustyiron]

I've experienced it ever since my 1st vehicle (74? CJ 5 with 304? v8) as a kid. Might have had something to do with the longer spring shackles and the 12x15 tires and the other monkeying around with the suspension. I learned very early not to be alarmed.
My "lift kit" matched my cherry bomb dual exhaust perfectly , oh the good dumb azzkid memories.

 

[5030]

My 350 is 6 over stock but I modded the suspension to accept that. Did a front axle flip on the front as well. Now that I'm old, I wish I didn't. Hard as hell to get into and out of. I might add that doing an axle flip is no easy matter, you have to be a good fabricator to accomplish it as it entails extensive welding. I did mine because I wanted a high portal front axle for clearaance. I also added an ARB air locker and a Tru Trak out back. and all my springs are running on greaseable Thompson linear roller bearings. In fact, every joint is greaseable including all the U joints. No death wobble on my 350. It's always tight and well greased. I run 36 x 10.50's MT mudders too on Alcoa forged aluminum wheels.

I did have to change the steering box mounts as the huck bolted mounts weren't up to the task. I welded up bolster mounts and drilled and tapped them for A325 high strength bolts.

Would I do it again? Nope.

 

[5030]

Of course it still rides like a lumberwagon unless it has at least a ton in the bed...,

 

[zzvyb6]

I have a proposal for any of you who can create this shimmy at any time they choose. I want to know if your problem is geometry or power steering caused. Yes you need to be equipped with power steering.
When it starts to dance, shift into neutral and floor the throttle. If available steering pressure is low because you got off the gas AND the pump is worn, then you could get the wobble to stop because now the power steering valve has more 'authority' due to the engine rpm increase.
You can also try to shut the engine off when it happens (don't let the steering lock up on you, crashing is not an option). If this works, the worn steering gear is actually the cause, with the engine off, no steering oil pressure, the valve feedback is disabled, and the blocked steering lines add a huge amount of damping.

Just a science project, but could help a LOT of folks here. One would be good enough for me.

 

[ovrszd]

I have a proposal for any of you who can create this shimmy at any time they choose. I want to know if your problem is geometry or power steering caused. Yes you need to be equipped with power steering.
When it starts to dance, shift into neutral and floor the throttle. If available steering pressure is low because you got off the gas AND the pump is worn, then you could get the wobble to stop because now the power steering valve has more 'authority' due to the engine rpm increase.
You can also try to shut the engine off when it happens (don't let the steering lock up on you, crashing is not an option). If this works, the worn steering gear is actually the cause, with the engine off, no steering oil pressure, the valve feedback is disabled, and the blocked steering lines add a huge amount of damping.

Just a science project, but could help a LOT of folks here. One would be good enough for me.

Not even close.

Readers, do not shutoff your engine going down the road during death wobble or any other time!!!!

 

[shooterdon]

I had it happen on my first and only Jeep. Bought it used about 6 years ago and traded it on an F150. The shop I took it to had no clue what to do. They wanted to start changing out parts Was not going to deal with it.

 

[5030]

Little backstory on FCA (and Stellantis). I retired from rhe outfit that supplied under sheetmetal components to them, actually over 85% and they would buy anything so long as it was cheap, cheaper the better. Never cared abour chems or certs either. Best thing they did was loose the Torqueflite and their gas motors. The Cummins and the Asian were good moves but the running gear is still junk and always will be and that includes the Jeeps.

If it's cheap, they buy it.

Good example are the valve rockers. Outfit south of Toledo heat treats all of them and makes them workable. Why they have issues with the valve trains on their gas motors. Junk.