Torqflow transmission, which is composed of planetary gear mechanism, multiple disk clutches and a hydraulic control unit, has been adapted for Construction Machine because it allows an easy selection of speeds (forward or reverse). Recently a rubber facing material with high coefficient friction has been used disk clutch's facing parts for compact design. Meanwhile, it's heat conduction is inferior to metalic disk to be usually used, so at engage time temperature of rubber facing disk is higher than metalic and it's ablasive wear ratio, which is verified to have influence on facing temperature by experiments, is increased far more than before. Therefore prediction of facing temperature has been more important than before. Now, in this report, study on transient thermal analysis is introduced because it's accuracy has come to practical level.