To provide a constant velocity joint for a vent valve protecting an internal joint cavity and joint grease from internal overpressure and external contaminants.

A vent valve for use in a constant velocity joint having a vent aperture in communication with a joint chamber comprises a body having a first end and a second end and at least one flat part extending therebetween; and an umbrella shaped flexible retention cap disposed adjoining the first end of the body and the at least one flat part. The retention cap is operative in a normally closed position to cover the at least one flat part and seal the joint from external contaminants, and in response to internal pressure created in the joint cavity, functions to bellow outward and expose the at least one flat part to permit air to escape from the chamber. At least one flat part includes a straight-line vent to clean the grease off and away from the vent valve. The vent valve can be made from single or multiple materials, having porous and non-porous properties.