I was at my local track today and noticed the car started to squirm to the left when I did a hard shift. I jacked the rear of the car and checked for play, sure enough there was slight play in the left rear wheel. Removed wheel and proceeded to feel around all the joints for play. The rear upper control arm inner joint was the culprit. I thought the joint was bad and I would have to replace the arm. I decided to check the bolt just in case and sure enough it was completely loose. I tightened the bolt and all is good. The bolt /nut is not easy to get to as the axle is right below the nut and there is only a small gap to get the bolt on top. Please check these bolts on your Z/28 if you track your car. The bolt is highlighted in the pic below. The left front wheel bearing failed as well on this day but that is unrelated.
