When 1 is selected, the manual valve supplies line pressure not only onto the differential area but also through a separate circuit to apply the rear band.
The application of the rear band provides engine braking on overrun.
This circuit passes through the bottom valley area of the valve and acts on the large bottomland to hydraulically lock the shift valve down.
Governor pressure cannot force an upshift, regardless of its value and the transmission remains in 1st gear until the lever is moved to 2 or to D, when an upshift can occur.
The rear band is inoperative whenever D is selected because the rear band is then open to exhaust at the manual valve.
Similarly, once the transmission has upshifted into 2nd gear, the rear band circuit is then open to exhaust at the shift valve.
When the transmission lever is placed in position 2, line pressure is directed to the front clutch, as in position D and to the governor and to the 1-2 shift valve.
The vehicle will move off in 1st gear and will change up to 2nd gear as soon as governor pressure becomes high enough to move the shift valve upwards and allow fluid to pass to the apply side of the front servo.
No further upshifts can take place since no line pressure is supplied to the 2-3 shift valve.
Even though the valve moves upwards under the influence of governor pressure, it is not controlling any fluid flow and no changes can occur.
