So I was test driving a z31 I want to buy but when driving it, when you let go of the clutch you hear a grinding sound. It doesn't happen when you shift or when your press down the clutch, only when the clutch is released. Any suggestions?

 

Figure in the cost of clutch replacement with the asking price of that Z31. Some aftermarket medium-duty clutch models are excellent, readily available, not too expensive if I recall. Check them out. Labor requires a lift to install it and bleed it right. If that's all that Z needs, sounds like maybe a good find. But spend as much time driving it as the seller will allow. It will tell you what else it needs or wants before you settle on a price.

 

It is most probably the throw out bearing. When press in on the clutch pedal, the throw out bearing is pushed against the "fingers" of the clutch plate. The pressure on the bearing will close up worn tolerances within the bearing and usually quiet it down. When no pressure is placed on the throw out bearing, the loose tolerances or worn races or ***** will become much louder. I agree with zxguy1986.
Thanks, Bob

 

maybe Bobs 84 or a imput shaft bearing
does it change when you bearly pressure the clutch pedal
what does it do when RPM's at 4K