Mechanical face seal has a first sealing (12) mounted in fixed axial and rotational relationship and sealed with respect to a housing (11) and a second sealing ring (20) mounted in fixed rotational relationship but movable axially with respect to a shaft (10). The second sealing ring (20) being sealed with respect to the shaft (10) by means of a bellows unit (22). One end (23) of the bellows unit (22) being engaged by a first drive band (30) which applies a radial load to the end (23) of the bellows unit (22) forcing it into driving and sealing engagement with the shaft (10) and the other end (25) of the bellows unit (22) being engaged by a second drive band (31) which applies a radial load to the end (25) of the bellows unit (22) forcing it into driving and sealing engagement with the second sealing ring (20). The inner ends (33) of the drive bands (30,31) are of equal diameter and have axially extending castellations (34), the castellations (34) of one drive band (30) intermeshing with the castellations (34) of the other drive band (31), whereby the drive bands (30,31) may be telescoped and torsional loads may be reacted between the shaft (10) and the second sealing ring (20) by the ends (23,25) of the bellows unit (22) and the drive bands (30,31). A spring (35) acts between the drive bands (30,31) to bias them apart and to urge opposed sealing faces (36,37) of the first and second sealing rings (12,20) into sealing engagement.