Chassis wiggle when off throttle?
 

Hello,

Mods in sig.

Current stock parts are rear UCA, stock motor mounts. Car has 97K miles.

When cruising at highway speeds, when I lift off the throttle, the car has a slight wiggle, like the front moves just a touch to the right and the rear moves to the left. Its very reproducible and unsettling and becoming more noticeable.

When I first installed the adj pan hard bar, I centered the rear wheels in the wheel wells. When I lowered the car, the body shifted a touch to the passenger side and I didn't adjust it back because I wasn't sure if centering it based on the body panels was correct or if I should center it based on a certain piece of the chassis.

Could it be from a worn out stock rear upper control arm?

Could it be from worn motor mounts?

Could it be from uncentered pan hard car, or incorrectly adj rear lower control arms?

Could it be chassis flex from a 10 year old car with 100K on it?

Could it be something else, like the differential or shocks?

Thanks everyone

I would look at the LCAs first. Adjustment is something that you'd notice from the steering wheel being un-centered while driving straight ahead on a flat road (little or no crown), or by noticing that when driving through a very gradual curve that the steering wheel is perfectly straight-ahead.

Poor LCA bushing condition can cause what you're describing (if it allows slight fore/aft movement of the axle on one side of the car but not the other - look at the left side first), as could play in the tie rods and/or ball joints.


Norm

Norm,

I got under the car tonight and at first glance the rear LCAs look tight and the roto joint is centered. However, while the bottom of the pumpkin is dry, it looks like a bunch of fluid has sprayed out from the front of the diff where the DS inserts. It's all over the exhaust, floor pans, and DS tunnel. Maybe the DS or something is failing? Bad seal? Could this be due to improper pinion angle? Could this be the cause of the wiggle when coming off throttle?

Are you also getting any 'clunking' when this happens?

How long have the Spohn LCAs been in there?


Norm

About 2 years for the LCAs

Wiggle/floating feeling from the front? Front control arms....

Did you inspect the horizontal bushings on those? Any cracks that are visible are bad on those things. I had replaced all the front end suspension components chasing a thunk and wiggle/floaty feeling. Got rid of the thunking with new sway bar bushings (main culprit), strut mounts (and struts) and sway bar links but the front end still felt unsettled. Replaced the front control arms and W O W! Night and day.

Here's a tip to test the front arms. I figured this out totally by accident.

Find a road with a sweeping left or right curve in the road (not a turn). Hit the curve at about 40-45 then accelerate modestly/briskly (don't floor it) to 55-60 (or even 70 if the law/road allows) as you go through the curve. The front should feel solid and stay planted, if you start getting a wobbly/floaty feel or what feels like a bouncing sensation, it's the control arm. Hopefully the road has some imperfections in the curve. Those will help trigger the unsettled feeling if the arm bushings are worn.

By accelerating in the curve you are unloading some weight from the front wheels and redistributing the remaining weight unevenly as you go through the curve For me, my front left was the worst and the most obvious. The front right was ok but not great.

After replacing the arms, no more wiggly/floaty feeling or bounce.

No wiggle or floaty feeling on turns from the front on smooth roads. The wiggle is more of a lateral wiggle like the car wants to rotate with the rear swinging clockwise when lifting off the throttle and now when applying the throttle. There is a little clunk in the center rear when jabbing the throttle at hwy speeds but I thought this was because I have a one piece DS and 4:10s and roto joints on the rear LCAs. The clunk in the front is only when hitting any road imperfections but on smooth roads and left or right turns don't yield any noise.

Is one end of each rear LCA poly-bushed?


Norm

Check out your Rear UCA. If it's still stock the rubber may be toasted so the clunking you are getting in the rear is the bushing allowing too much play (contacting metal to metal)

Clunk or logs rolling along sound from the front is most likely the sway bar bushings. Mine were disintegrated. Jack the front end up so the weight is off the tires. Grab either end of the sway bar (driver/passenger) and Try to shake it. It should not move at all. Visually the bushings should have no cracks. They are a one-piece so any cracks means they are worn out.

If removing the sway bar to replace the bushings, it's best to remove the bar with the sway bar links still attached. That means you'll have to undo the link from the strut, not the bar. Then remove the links from the bar once you have the assembly out of the car. When you put it all back together, reconnect the links to the bar first, then put the assembly back in the car. The reason is, if you try to put the bar back onto the links while it's all in the car, you won't be able to properly torque the bolt for the Sway Bar Link to Sway Bar. The way the sway bar/end link sits there is no room to get a socket with a TQ wrench in there and reliably torque the parts together. Not enough torque on the sway bar end link nut to sway bar is also a reason for clunking.

Body is poly end, axel is roto joint