Hydraulic pressure is applied to the servo valve to engage the reverse selector with the countershaft reverse gear while the shift lever is in the position.
Hydraulic pressure is also applied to the 4th clutch, then the 4th clutch engages the mainshaft reverse gear with the mainshaft.
The mainshaft reverse gear drives the countershaft reverse gear via the reverse idler gear. The countershaft reverse gear drives the reverse selector, reverse selector hub and the countershaft.
The rotation direction of the countershaft reverse gear is changed via the reverse idler gear.
Power is transmitted to the final drive gear, which in turn drives the final driven gear.