Release bearing assemblies for vehicle clutches

In a vehicle clutch release mechanism comprising a clutch operating lever and a clutch release fork, a release bearing assembly comprising inner and outer sleeves arranged to slide axially relative to each other and located around the shaft of the gear box of the vehicle, the inner sleeve being operatively connectable with the operating lever of the clutch, the outer sleeve being connectable with the release fork of the clutch and being arranged to assume a predetermined position relative to said gear box when the clutch is engaged and being movable axially away from said position when the clutch is released, a nut threadably engaging the exterior of the inner sleeve, abutment means carried by said outer sleeve and arranged in use to act on said nut so that said inner sleeve moves axially with the outer sleeve when the clutch is released, clamping means arranged to engage said nut to hold said nut against rotation when the sleeves are moved axially during clutch release, and release means for releasing the clamping means from engagement with said nut as said outer sleeve approaches the predetermined position under the influence of the operating lever of the clutch, so that the nut can rotate, under the influence of an axially force derived from the operating lever, about the inner sleeve to allow the inner sleeve to move axially relative to the outer sleeve when the outer sleeve is in its predetermined position.