this slot to act as a rough filter for the transmission 30 a flow of continuous cooling air to the clutch disks 102 103 104 104a 105 105a 106 107 108 and 109 is occasioned by internal blading fig4 in hubbed gears 92 94 such as vanes 111 a total of 10 in hubbed gear 92 these vanes are arranged to form a centrifugal fan configuration 113 the blades draw air from six circumferential slots 115 in hubbed gear 92 arranged equidistantly and extending axially through the geared portion of hubbed gear 92 hubbed gear 94 has similar slots 117 six the flow of cooling air in the geared hub 92 fig8 and 16 passes between an internal periphery of it and the radial outer extent of the clutch disks e g disks 102 104 104a 106 and 108 through an axially extending series of channels 119 five between the ribs of the hubbed gear 92 this provides an outer flow of cooling air for the clutch disks an inner flow is also provided through a stepped channel 121 formed between the inner bore periphery of the clutch disks 102 104 104a the indented spaces between the splines on splined piece 114 and around the splines and through oblong slots 123 five in the clutch disks 106 and 108 air follows these inner and outer paths to finally exhaust through slot 176 hub.