Toro Groundsmaster 4500-D Series Service Manual page 121

Forward Direction (continued)
Reverse Direction
Groundsmaster ® 4500-D/4700-D
19245SL Rev A
When going down a hill, the tractor becomes an over-running load that drives
the front wheel and rear axle motors. In this condition, the rear axle motor could
lock up as the oil pumped from the motor increases pressure as it returns to the
piston pump. To prevent rear wheel lock up, an adjustable relief valve (RV) in
the rear traction manifold reduces rear axle motor pressure created in down hill,
dynamic braking conditions.
The traction circuit operates essentially the same in reverse HI range as it does in
the forward direction. However, the flow through the circuit is reversed. Oil flow
from the piston pump is directed to the front wheel motors and also to the rear
traction manifold. The oil to the front wheel motors drives them in the reverse
direction and then returns to the piston pump. The oil to the rear traction manifold
enters the manifold at port P2 and flows through pressure reducing valve (PR)
which limits the down stream pressure to the rear axle motor to 27.6 bar (400 PSI)
so the rear wheels will not scuff the turf during reverse operation. This reduced
pressure flow is directed out rear traction manifold port M8 to drive the rear axle
motor in reverse. Return oil from the rear motor returns to the piston pump.
Page 5–19 Hydraulic System: Hydraulic Flow Diagrams