lx300

I own a 99 sc300 with 18" wheels ,lowered 1" frnt/1.5" rear. stock motor ... 40,000mi when bought. I'm the 2nd. owner for the past year...At purchase it had a shake I could feel in the steering wheel at 65mph. Not as noticeable slower or faster. It had new tires with stock wheels. I installed the new wheels/tires and lowering springs.... Same problem!... I have had the car aligned and tires balanced and checked for roundness and rotated several times searching for the source of the steering wheel shimmy. All bushings seem to be good. No excess play in the bearings, ball joints good....Any ideas???