Shimmy revisited, and another non-bushing fix
|Posted by: Jason
on 2002-05-20 at 09:29:47
from: Host: cust-216-59-192-54.t-speed.net IP: 126.96.36.199)
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.
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
- 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)
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)
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.