A pneumatic clutch actuator , comprising: a housing assembly having a first housing member and a second housing member that at least partially receives the first housing member , the first housing member is provided with an inner annulus that is disposed about a transmission input shaft; a bearing assembly disposed on a portion of the housing assembly, the bearing assembly having a bearing carrier that supports a bearing ; and a piston assembly slidably disposed within the housing assembly and movable between a first position and a second position to selectively change a clutch assembly between an engaged state and a disengaged state; characterized in that an adjustment assembly is disposed between the bearing assembly and the piston assembly , the adjustment assembly configured to adjust a total length of the piston assembly to compensate for wear of the clutch assembly, and the adjustment assembly comprises: a first adjustment member disposed on a piston head of the piston assembly ; a second adjustment member disposed about the inner annulus and disposed between the bearing carrier and the piston assembly , wherein the second adjustment member defines a friction surface ; and a guide member disposed about the second adjustment member and received within the first housing member , wherein in response to the piston assembly moving towards the second position, the first adjustment member is configured to engage the friction surface to inhibit relative rotation between the second adjustment member and at least one of the first adjustment member and the piston assembly . a housing assembly having a first housing member and a second housing member that at least partially receives the first housing member , the first housing member is provided with an inner annulus that is disposed about a transmission input shaft; a bearing assembly disposed on a portion of the housing assembly, the bearing assembly having a bearing carrier that supports a bearing ; and a piston assembly slidably disposed within the housing assembly and movable between a first position and a second position to selectively change a clutch assembly between an engaged state and a disengaged state; characterized in that an adjustment assembly is disposed between the bearing assembly and the piston assembly , the adjustment assembly configured to adjust a total length of the piston assembly to compensate for wear of the clutch assembly, and the adjustment assembly comprises: a first adjustment member disposed on a piston head of the piston assembly ; a second adjustment member disposed about the inner annulus and disposed between the bearing carrier and the piston assembly , wherein the second adjustment member defines a friction surface ; and a guide member disposed about the second adjustment member and received within the first housing member , wherein in response to the piston assembly moving towards the second position, the first adjustment member is configured to engage the friction surface to inhibit relative rotation between the second adjustment member and at least one of the first adjustment member and the piston assembly . a first adjustment member disposed on a piston head of the piston assembly ; a second adjustment member disposed about the inner annulus and disposed between the bearing carrier and the piston assembly , wherein the second adjustment member defines a friction surface ; and a guide member disposed about the second adjustment member and received within the first housing member , wherein in response to the piston assembly moving towards the second position, the first adjustment member is configured to engage the friction surface to inhibit relative rotation between the second adjustment member and at least one of the first adjustment member and the piston assembly . <EOS>