Need Help with Shimmy Diagnosis (Long)

[talltorontoguy]

Hey guys, need some help on this one.

I know its long but want to give as much info as possible. I don't believe this to be the thrust arm issue (explanation below).

I'll give you an order of events leading up to this issue. Please note that this shimmy appeared suddenly after the unfortunate incident below.

1. Had a known lower control arm issue (ball joint failure). No significant shimmy, did have a slight shimmy and figured due to lower control arm.

2. Put on summer wheels, headed out to have lower control arm replaced. No significant shimmy at any speed.

3. 1/2 way there, thought had flat - Looked out... no flat (express lanes, couldn't get out) Had to drive about 2kms to get off highway, turns out left rear wheel had started to come off on highway (didn't torque nuts properly).

4. Took off wheel, found hubcentric ring in tatters (ground down). Retightened wheel and continued - now have major shimmy at 80 to 100 kph (50 to 60 mph) - coming through both seat and wheel. Thought it was due to absence of ring.

5. Replaced lower control arm. Replaced hubcentric ring. Noted left subframe bushing dropped slightly. Significant shimmy still present.

6. Had wheels re-balanced. Balanced fine with no apparent issues. Significant shimmy still present.

7. Replaced wheels and tires with another set. Significant shimmy still present.

notes:

- seems to be less when veering left at speed (off ramp)
- seems to be less under braking
- more apparent during acceleration or maintaing speed
- rotors are not warped
- thrust arms done with 750 bushings
- rear end seems to be 'loose' (thought was subframe bushing)

----------

My analysis:

1. Cannot be wheels

2. Should not be front suspension (thrust arms done w/750 bushings within last 24 months). Plus, the issue was not present before wheel came off.

3. Possible that the vibration from wheel coming partially off may have damaged an already weak bushing in rear?

4. Possible that the wheel coming partially off may have damaged something in rear drivetrain?

----------

Does anyone have any ideas for me on this one? I want to try to avoid playing the "replace and see" approach. Any tips or other diagnostic procedures would be great.

Thanks guys,

Rod

[talltorontoguy]

Anyone?

[632 Regal]

I was afraid to give you my thoughts but it looks like you need some. You have to check everything in your front suspension for play, these cars are very susceptible to shimmy, 1/2 oz off on one wheel will make the steering shake so let alone out of round tires, slightly bent or out of round rims, go to the tire store and ask if they will let you watch them spinn the tires, might be out of round. You could have an egg tire that balances but goes up and down as you drive. Thats not good on a bimmer or anything for that matter. I think you may have gotten a raw deal with the loose lugs and all and have nore than one single problem here. Start with the tires/rims then go to the front end for play, replace and from there poat again?
Best of Luck
this isnt an easy target your looking to nab
Jeff (the virus spreader)

[talltorontoguy]

Thanks Jeff,

I've already done the tire thing, having had them balanced, and finally replacing all tires and wheels with another set. So that's ruled out.

Control arms are in good shape, although I suppose it it posssible that an upper control bushing has worn again.

What would cause such a shimmy in the rear end of this car?