For front propeller shafts of 4WD vehicles, the transfer side universal joint does not have sufficient heat resistance. If the temperature of the joint increases due to the heat created during high load travelling such as when high speed travelling or uphill travelling, the grease may prematurely lose lubricating property. If this problem is left unattended, the joint may wear further, causing rattling and abnormal noise, and in the worst case, the joint could break, which would make it impossible to drive the vehicle.