A clutch release bearing, sometimes referred to as a throw out bearing, is a thrust bearing that contacts the fingers of the Pressure Plate. It provides a spinning surface to engage and disengage the clutch. A clutch release bearing can be actuated hydraulically or mechanically, but its function never changes.
Hydraulic vs Mechanical
A mechanical release bearing is actuated by a clutch fork that rides on a pivot inside the bell housing. The clutch fork is moved with a linkage commonly referred to as a Z-bar, by a cable, or by a hydraulic cylinder pushing or pulling the fork.
Hydraulic release bearings are actuated by hydraulic fluids being forced into a hydraulic cylinder that’s mounted inside the bellhousing. This forces the bearing forward.
Note:
In many cases, hydraulic release bearings require a preset air gap of 0.150 in - 0.200 in. This ensures that as the clutch wears,the bearing and pressure plate fingers don’t touch when the clutch is disengaged. Follow this link to the OnAllCylinders blog to learn more about Setting Your Clutch Air Gap.