RETAINER 7S2994 - Caterpillar

Piston Motor (Rear Propel)
Illustration 1 g01233763
Propel Motors
A piston type motor drives each rear wheel through a two-speed planetary final drive. The ports on the motors are marked for identification. On the right motor, port "A" is the reverse port and port "B" is the forward port. On the left motor, port "A" is the forward port and port "B" is the reverse port.Speed Sensor
Each motor is equipped with a speed sensor (right shown). A gear on the output shaft of the motor rotates past the tip of the speed sensor. Each time a tooth passes the sensor, an electrical impulse is sent to the machine ECM. The machine ECM converts the frequency of the electrical impulses to a vehicle speed.Flushing Valve
Each propel motor contains a flushing valve. Flushing valves direct oil from the low pressure side of the propel loop to the flushing relief valve. The flushing relief valves open when the pressure in the low pressure side of the propel loop is greater than the flushing relief pressure setting. Each flushing relief valve directs a metered amount of oil from the low pressure side of the loop into the motor case drain. The case drain line on each motor directs oil from the motor cases to the cooler bypass manifold.Propel Motor Cross Section
Illustration 2 g01233771
Rotating Group
The right and left propel motors are identical. The propel motor is a fixed displacement, piston type motor with a loop flushing valve.When the machine is moving, supply oil from the propel pump group enters the motor. Supply oil is directed to the inlet port of the valve plate. Supply oil is also directed to the flushing spool. The valve plate directs oil into the piston chamber in the cylinder block. This pressure forces the pistons which are aligned with the inlet port to move out of the cylinder block.As the pistons are forced out of the cylinder block, the slipper feet slide along the swashplate. This causes the cylinder block and pistons to rotate. Since the cylinder block is splined to the output shaft, the output shaft also rotates.As the cylinder block rotates, pistons align with the outlet port in the valve plate. The rotation of the cylinder block forces oil out of the piston chambers and into the low pressure side of the hydrostatic loop. Low pressure oil acts against the flushing valve. The low pressure oil then returns to the inlet side of the hydraulic pump, which completes the hydrostatic circuit.Flushing Valve
High pressure oil acts against one side of the flushing spool, and low pressure oil acts against the other. The force from the high pressure oil causes the flushing spool to shift. The shift opens a passage for oil in the low pressure circuit in order to act against the flushing relief valve. The flushing relief valve opens, which allows oil in the low pressure circuit to flow into the motor case drain.