Bill,
Where in the car is the shuddering?
If it's the steering wheel, look for tire balance, roundness of the
front wheels and wobble of the front wheels. Balance work means that the
tires go to the shop, but roundness you check by jacking up the front,
holding a pencil on a cinder block, and turning the wheel to see if it
turns evenly past the pencil point. Similarly, check for wobble by
watching the wheel move in and out (left/right) against the pencil point.
ANother test is to swap front wheels to rear and go driving. Is
vibration same, different, now at the rear, etc?
Also check the fluid level in the dampers. If they are dry, they can
permit an inbalance in a wheel really get the wheel hopping.
Another possibility is that the universal joints are wearing (loose)
and the coupling bolts are loose. These are worth checking every so often
anyway. Grab the driveshaft and shake it vigorously. There should be no
movement in any direction at the u-joints, and none either at the
couplings.
Also, just check that all wheel bolts are tight--they should be
tightened 1 3 4 2, or in some pattern of alternate tightening, so that
the wheel is centered most perfectly on the bolts. Few shops do this,
alas, but they do over-tighten the bolts.
There are times in which balance problems appear as harmonics--one item
vibrates and another item vibrates at different frequency. SOmetimes they
damp themselves away and sometimes the vibration RESONATES, and you go
nuts trying to figure out the combination of ingredients in the puzzle.
Bob
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