My cousin noticed a slight vibration in my SBC powered TH400 and suspected the driveshaft yoke bushing in the tranny. He crawled under the car and shook the drive shaft up and down and sure 'nuf, there was some play and an audible clunk. When I recently had the drive shaft out to have it balanced and u-joints replaced I didn't notice any abnormal wear on the yoke. Does anyone have an idea what the tolerance should be? I'm thinkin' a clunkin' noise is not good.