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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
Discussion Starter #1
One of these days, I'm going to teach the boys how to fix their own cars. I get these cars back every 12-18 months, with lots of little annoyances. Already posted on oil adapter orings and smog pump cover. Figured I would document this next problem here.

Son had told me about done sort of rattle at 40-45. Drove it numerous times, found nothing. Noticed the front tires were shot when replacing the orings, so scheduled a trip to the tire shop.

Put on new ones the front, drove the car 30 miles at 80, nothing unusual. (There may have been a shimmy, but negligible). Next day, flat in the rear right (when it rains, it pours). Swapped cars with him again, pulled the tire, had it plugged, back on, 30 miles and guess what, a shimmy.

Starts at 60, gets worse up to 80 and even worse when letting off the accelerator. I'll stay the fsm diagnostics this weekend and post here.

One theory on the sudden appearance. Shimmy is rotational based and the tire-, wheel, axel had settled into it. Pulling the tire/wheel and reinstalling rotated a bit caused the original settle in to be out of balance.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,409 Posts
Yup - all one needs to do is look incorrectly at a FWD Northstar car and you get the "Seville Shimmy".

Wheel, tire out-of-round, dirty wheel/disc/hub mounting surfaces, rotor deposits (they don't "warp"), loose suspension components/bushings, improper lug nut torque/sequence, Road Force balancing, tire wear/cupping.
 

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99 Seville STS
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323 Posts
Unpredictable it is,

I decided to swap the back tires with the front as the back are newer and have better pattern to even out the wear, and suddenly the shimmy I had last season was almost gone.

Interesting theory about the rim position making a difference, maybe we should make a mark on the rim and hub to get the wheel back on in the same position again, when shimmy is gone that is, could be worth a try…
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
Discussion Starter #5
Yup - all one needs to do is look incorrectly at a FWD Northstar car and you get the "Seville Shimmy".

Wheel, tire out-of-round, dirty wheel/disc/hub mounting surfaces, rotor deposits (they don't "warp"), loose suspension components/bushings, improper lug nut torque/sequence, Road Force balancing, tire wear/cupping.
Got some bourbon, 2am, pulled the wheel/tire. Shook, shake, pry, pull, dance, jig. . .no movement anywhere on the suspension. No rust (TX), bushings good, rotor good, no unusual tire wear.

So, assume that the tire is it is not balanced. Weight from original purchase is still I have. Wonder if the plug threw it out of balance. Will pull it again this weekend to get balanced. Will find a road force shop.
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
Discussion Starter #6
Some more feedback on driving. Found out the vibration disappears at 82. It's just disappears, nada, nothing.

Took the tire to one of the National chains to get road force balanced. They wouldn't touch it as I didn't have them repair it. (Years of watching lawyers slowly impact the operation of the retail tire operation , basically, too many customers find a way to blame the tire company, that the tire company has had to go to a policy of not repairing anything that has a chance of failing in the future as a failure at 70 mph might kill someone).

So, took it to the local operation and had it regular balanced. Took 3 tries (ie 1 big weight split into 2 and then a 3rd). That resulted in a 10-15% improvement.

Got son to drive while I followed. Tire is bouncing
.5" in all directions. Hhmm, shock time. (And wondering why that old school, bounce the corner method, didn't reveal a problem). Now to find those Basscat posts.
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
Discussion Starter #7
Son didn't want to wait. . So monroe ma822 from the auto store (and a top mount to be safe). Installed (2 hours with floor jack, stand, and bourbon).

Result, still there, but better.

Old shock. Did find a "weak" travel point on the shock from the bad side. Comparing the compression rate when pushing both, that bad one had a clear give out from 25% to 50% travel rate. So, combined with a spring, I doubt I would have found it trying to shade tree, bounce the corner.

On the drive, it was noticeably better at the lower speeds (had felt it at 45, but now at 60). Still cuts off at 82.

Did try a few things.
  • after cut off at 82, I let it coast to point of vibration. Vibration started at 75.
  • I could continue driving from 76 and above with no vibration.
  • thinking, the vibration frequency feels like an a frequency. Tried turning off traction control. No change.
  • pulled codes, just the typical battery disconnected history messages. Nothing for abs, pcm etc.
Tommorrow, will try moving the new front tires to the rear to see if the problem follows the wheels.
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
Discussion Starter #8
Well, two balances and a set of shocks later, it's finally fixed.

Turns out, ~2 cups of water in the tire.

Took it to get road forced. Had the normal conversation around what happened, what's been done etc. Typical answers of it might need new tires, the wheel is bent, the hub is messed up etc.

They put it on the machine, and scratched their heads. The wheel is perfectly round. But the separate runs produced different results. It took the old guy to suggest that there might be water in the tire.

Sure enough, ~2 cups. Cleaned the tire, cleaned the wheel (lots of bead seal from Colorado cold college years), balanced, installed, runs great.

The shimmy explanation:
  • on low speeds, under 50, the water is able to slosh/move around the tire
  • from 50-75, the "slug" of water is held in place against one point inside the tire, putting it out of balance. It's able to stay in place was the tire flexes to create a dimple/cup to enclose the water.
  • at 80+, the centrifugal force causes the slug of water to spread out around the tire, putting the tire back in balance
As to how it got there
  • old guy cheap tire places, or the gas station fills are not filtered and could be introducing water.I could see that happening, but does not explain the suddeness introduced after the tire repair.
  • later, it dawned on me, the tire repair process included cleaning the hole and possibly washing the tire out of any rubber material. Likely, they did not dry the tire out enough before remounting.
 
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