Universal or Cardan joints of a power shaft are joined by an axially sliding coupling which is sealed by a combination bearing and wiper having a low co-efficient of friction. One of the universal joints has an internally splined hub receiving an externally splined pin on an intermediate shaft secured to the other joint so that the axial spacing of the two joints can be varied without loss of power transmission. A sleeve or pipe secured at one end to the pin surrounds the hub and carries in its other end a plastics material sealing ring with a rigid bearing portion and a flexible lip portion riding on the hub to hold the sleeve concentrically around the hub and seal the chamber between the sleeve and hub.