COVER GP-FRONT HOUSING 1181727 - Caterpillar

When in forward, passage E remains at atmospheric pressure since slot K remains open to sump.When a shift is made from forward to neutral, the valve stem is rotated to the position illustred by figures 3-1 and 3-2. Under these conditions, passages E, F are connected to sump by slot K. Passage I is also connected to sump by port J in the valve stem. Since passage F is connected to slot K, oil drains rapidly from the forward clutch to sump. Since passage I is now at atmospheric pressure, the oil pressure in chamber L unseats the steel ball against the compression spring, permitting a rapid oil drain from chamber L to sump and allowing the rate-of-rise piston to move back against the orifice plate. The forward clutch is now disengaged and main system pressure reduced to neutral pressure.
Figure 3-3 : Control valve - Forward - Sectional view.
Figure 3-4 : Control Valve - Forward - Cutaway View.Control valve-reverse (fig. 3-5 & 3-6).
When a shift to the reverse position is desired, the control valve lever is moved to pump side direction. The shift causes the control valve stem to rotate and assume the position indicated in figures 3-5 and 3-6. The pressurized oil in chamber B is directed through passages H and E. Passage E is aligned with a drilled hole and a channel in the manifold directing main pressure to the reverse clutch. Pressurized oil from port G travels through passage I and enters chamber L through an orifice in the orifice plate.The orifice in the plate meters the oil for a steady, smooth pressure rise in chamber L. As chamber L fills with oil, the rate-of-rise piston moves against the piston springs until the piston is stopped by a shoulder in the valve body. This causes the pressure in chamber B to rise to clutch engaging pressure.When in reverse, passage F remains at atmospheric pressure since slot K remains open to sump. When a shift is made from reverse to neutral, the valve stem is rotated to the position illustrated by figures 3-1 and 3-2. Under these conditions, passages E, F are connected to sump by slot K. Passage I is also connected to sump by port J in the valve stem. Since passage E is connected to slot K, oil drains rapidly from the reverse clutch to sump. Since passage I is now at atmospheric pressure, the oil pressure in chamber L unseats the steel ball against the compression spring permitting a rapid oil drain from chamber L to sump and allowing the pressure rate control piston to move back against the orifice plate. The reverse clutch is now disengaged and main system pressure reduced to neutral pressure.
Figure 3-5 : Control Valve - Reverse - Sectional view.
Figure 3-6 : Control Valve - Reverse - Cutaway View.Trolling Valve (Optional equipment).
General.
The trolling valve contains passages and ports to work in conjunction with the control valve for the transmission and direction of pressurized oil within the hydraulic system