Clutch Pilot Bearing
The clutch pilot bearing is a ball or roller bearing or a brass bushing that centers the transmission's input shaft in the crankshaft flange.
It reduces friction caused by the rotating crankshaft as the input shaft slows.
A faulty pilot bearing is loudest when the clutch pedal is fully depressed, and the clutch is disengaged. The input shaft and the crankshaft flange are now rotating at different speeds. They produce a squeal or grinding sound when the clutch is disengaged.
Pilot bearings are inexpensive and often replaced when replacing the disc. If faulty, the transmission is separated from the engine. They can be difficult and usually require a special puller to remove. Use the appropriate driver and make sure to tap on the outer race only.