The Shimmy revisited, and another non-bushing fix
Posted by: Jason on 2002-05-20 at 09:29:47
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Had bushings done last year, which cured The Shimmy for a while. Slowly crept back. Had tires balanced last week, fixed for a day but came back, albeit not nearly as noticible as before (balancing was a non-Hunter machine, as the last Hunter balancing did not fix the Shimmy so why waste the cash, also got a free balancing at NTB).

Anyhow ... at suggestion of another member here had a look at tire pressures. 33lbs all around, which is not spec at all - oops. Raised front to 36 and rear to 42 (both a little high, but works well) and voila, shimmy gone again!

Looks as if all unsprung mass must be in tip-top shape to keep The Shimmy at bay: bushings, wheels, tires. I noticed when spin balancing my tires that one of them had a really tiny wobble to it and given that the tires are due for replacement soon, when I replace then hopefully that will push The Shimmy further away.

Shimmy Checklist:
- are tires balanced? (maybe a weight fell off, maybe have worn over time)
- are tires inflated to BMW spec pressures? (look inside driver's doorjamb for correct pressures; pressure stamped on sidewall is merely a generic recommendation)
- are tires "true" and round? Any flatspotting?
- are wheels true to centering hubs? (centering hub must be clean, wheel touqued properly to hub/rotor assembly, mating surfaces must be clean)
- are rotors true and torqued to clean hub assembly? (be precise when doing a rotor replacement, torque down using "star" pattern with lug bolts before affixing wheel, then fasten down using hex bolt, then remove lugs and replace wheen following same procedure)
- are front thrust arm bushings in good shape? (look for hydraulic fluid leak from bottom of bushings)
- have balanced rotors been used if rotors replaced? (non-OEM rotors may not have the balancing cutouts on the edge, get OE or OEM to avoid this issue)

My shimmy is thankfully gone - again - and I love my car. Again. If you have shimmy issues try the items in the list in order before resorting to bushing replacement. Last year I was able to fix it for quite a while by simply reassembling and torquing rotors/wheels after cleaning all mating surfaces. The precision aluminum suspension gives the E39 its wonderful balance, but makes it quite sensitive to any imbalances which manifest as a shimmy. All must be perfect.

Good luck.