Systems Operation

966G Series II Wheel Loader and 972G Series II Wheel Loader Power Train

POWER TRAIN
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g00293356
Illustration 1
Location of Power Train Components

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(1) Diesel engine

(2) Torque converter

(3) Transmission

(4) Output transfer gears

(5) Rear final drives

(6) Rear drive shaft

(7) Front drive shaft

(8) Front final drives

Power from the diesel engine (1) is sent from the flywheel to torque converter (2). The torque converter is splined to the engine
flywheel. The torque converter is fastened to transmission (3) by bolts. Power flows directly from the torque converter to the
transmission input shaft. The torque converter output gear is meshed to the transmission input gear.

The transmission output shaft is connected to the input gear in output transfer gear case (4) by splines. Power is sent through the input
gear to the output gear. The output gear sends power through rear drive shaft (6) to the rear differential. The output gear also sends
power to the front differential through front drive shaft (7). The bevel gear and pinion of each differential sends the power to the final
drives through the differentials and through the sun gear shafts. Axle shafts transfer the power from final drives (5) and (8) to the
wheels. An integral parking brake is mounted on the front of the transmission.

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 The hoist in order to remove torque converter assembly (6) from the transmission planetary group. The weight of the torque
converter assembly is 190 kg (420 lb).

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Torque Converter
SMCS - 3101
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The torque converter is located at the input end of the transmission. The torque converter housing is bolted to the flywheel housing.
Output torque from the torque converter enters the planetary transmission through either the Number 1 sun gear or the Number 2 sun
gear. The gear that receives the output is dependent upon the direction clutch that is engaged.

Oil for the operation of the torque converter is supplied by the transmission oil pump. Oil from the transmission oil pump flows to the
torque converter housing. The oil flow is divided in the torque converter housing. The transmission hydraulic control relief valve and
the clutch solenoid modulating valves receive the oil flow that is divided. The transmission hydraulic control relief valve regulates P3

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converter inlet oil to flow to the torque converter at a nominal pressure of 550 kPa (80 psi). The torque converter inlet relief valve
limits the oil flow to the torque converter to a maximum pressure of 900 ± 70 kPa (130 ± 10 psi). The torque converter inlet relief
valve is located in the torque converter housing. The transmission hydraulic control relief valve is located above the torque converter
inlet relief valve.

The torque converter outlet pressure is 415 kPa (60 psi).

Torque Converter

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5
 g00431438
Illustration 1
Torque Converter

(1) Rotating housing

(2) Impeller

(3) Gear

(4) Inlet port

(5) Output shaft

(6) Turbine

(7) Stator

(8) Adapter

(9) Carrier assembly

(10) Outlet port

Rotating housing (1), impeller (2), and oil pump drive gear (3) are driven by the flywheel. These components rotate as a unit at the
engine speed.

P3 converter inlet oil enters the torque converter through inlet port (4) in carrier assembly (9). The oil is directed to the inlet port by a
passage in the torque converter housing. From inlet port (4), the oil flows through carrier assembly (9) and through a passage in
impeller (2) .

As impeller (2) rotates, the impeller acts as a pump in order to direct the oil to turbine (6). The turbine is fastened to the hub assembly
with bolts. The hub assembly is connected to output shaft (5) by splines. The turbine directs oil to stator (7) that is held stationary. The
stator is connected to adapter (8) with splines. Adapter (8) is connected to carrier assembly (9) with splines. Carrier assembly (9) is
bolted to the torque converter housing .

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The oil flows through a passage in carrier assembly (9) to outlet port (10). From outlet port (10), oil is directed to the torque converter
oil cooler. The temperature of the oil is lowered in the torque converter oil cooler. From the torque converter oil cooler, the oil flows
to the transmission. The oil cools the internal components of the transmission. The oil lubricates the internal components of the
transmission.

Torque Converter (Freewheel Stator)

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8
 g00908952
Illustration 2
(1) Rotating housing

(2) Impeller

(3) Gear

(4) Inlet port

(5) Output shaft

(6) Turbine

(7) Plate

(8) Stator

(9) Race

(10) Carrier assembly

(11) Outlet port

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 g00908953
Illustration 3
(9) Race

(12) Cam

(13) Spring

(14) Slot

(15) Cam surface

(16) Roller

Rotating housing (1), impeller (2), and oil pump drive gear (3) are driven by the flywheel. These components rotate as a unit at the
engine speed.

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P3 converter inlet oil enters the torque converter through inlet port (4) in carrier assembly (10). The oil is directed to the inlet port by a
passage in the torque converter housing. From inlet port (4), the oil flows through carrier assembly (10) and through a passage in
impeller (2) .

As impeller (2) rotates, the impeller acts as a pump in order to direct the oil to turbine (6). The turbine is fastened to the hub assembly
with bolts. The hub assembly is connected to output shaft (5) with splines. The turbine directs oil to stator (8) that is held stationary.

Stator (8) is connected to freewheel cam (12) with splines. Stator (8) and freewheel cam (12) rotate together. Freewheel race (9) is
held stationary. Springs (13) are inserted between cam (12) and rollers (16). Race (9) is connected to carrier (10) with splines. Carrier
(10) is fastened to the cover that is around the torque converter. Carrier (10) and race (9) do not rotate. The carrier helps to support the
rotating components of the converter. The carrier also contains the oil flow passages for the operation of the converter.

The oil flows through a passage in carrier assembly (10) to outlet port (11). From outlet port (11), oil is directed to the torque
converter oil cooler. The temperature of the oil is lowered in the torque converter oil cooler. From the torque converter oil cooler, the
oil flows to the transmission. The oil cools the internal components of the transmission. The oil lubricates the internal components of
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the transmission.

Torque Converter and Pump Drive Housing

SMCS - 3101; 3105; 3108
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 g00431978
Illustration 1
Torque Converter and Pump Drive Housing

(1) Torque converter housing. (2) Transmission and hydraulic implement pump drive gear. (3) Pump drive flange. (4) Transmission oil pump. (5) Torque
converter. (6) Transmission housing. (7) Torque converter output gear. (8) Drive gear. (9) Input gear for planetary transmission.

Transmission oil pump (4) and the hydraulic implement pump are mounted on torque converter housing (1). Torque converter housing
(1) is between the engine flywheel housing and transmission housing (6) .

Gear (8) turns drive gear (2) for the transmission oil pump and for the hydraulic implement pump. Pump drive flange (3) is connected
to transmission oil pump (4) by splines. The hydraulic implement pump is fastened to transmission oil pump (4). Torque converter
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output gear (7) sends power to input gear (9) for the planetary transmission.

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 g00772653
Illustration 2
Block Diagram of the Power Train Electronic Control System

(9) Position sensor (left pedal)

(10) Transmission direction and speed control

(11) ET service connector

(12) CAT Data Link

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(13) Caterpillar Monitoring System

(14) Caterpillar Monitoring System service connector

(15) Power train electronic control module (ECM)

(16) Auto/manual switch for the Autoshift control

(17) Transmission neutralizer override switch

(18) Variable shift control switch

(19) Minimum engine speed setting

(20) Engine

(21) Engine speed sensor

(22) Torque Converter

(23) Torque Converter output speed sensor

(24) Modulating valves (transmission clutch) (six)

(25) Transmission oil temperature sensor

(26) Transmission output speed sensors (two)

(27) Differential

(28) Transmission

Six hydraulically activated clutches in transmission (28) provide four forward speeds and four reverse speeds. Speed selections and
direction selections are made manually with transmission direction and speed control (10). The autoshift control will make speed

15
selections if the machine is in automatic mode. The variable shift control uses the position of the variable shift control switch and the
engine speed in order to provide alternate auto shift points.

The power train electronic control system electronically controls transmission shifts. The power train electronic control system shifts
the transmission. In order for the transmission to be shifted to the desired speed and the desired direction, power train ECM (15)
receives the operator input from transmission direction and speed control (10) and the left brake pedal position sensor. The power train
ECM signals the modulating valve (transmission clutch) of the speed clutch that is selected. The power train ECM signals the
modulating valve (transmission clutch) of the direction clutch that is selected. The output signal energizes the solenoids of modulating
valves (transmission clutch) (24) that are selected. The energized modulating valves (transmission clutch) electronically modulate the
oil pressure of the clutches that are selected. The power train ECM can request automatic shifts. The power train ECM uses the
following input signals to ensure steady engagement of the clutches: engine speed sensor (21), torque converter output speed sensor
(23), transmission speed sensors (26) and transmission oil temperature sensor (25) .

The power train ECM also controls the following functions: neutral start, ride control, backup alarm, auto shift control, variable shift
1 1

control, secondary steering, speed limiter, parking brake interlock and transmission neutralizer.
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Sensors
SMCS - 1907; 1912; 301T; 3141; 3175
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Sensors provide information to the power train electronic control module (ECM) about changing conditions. The sensor signal
changes proportionally to the changing conditions. The following type of sensor signals are recognized by the power train ECM:

 Frequency signals: The frequency (Hz) of the sensor signal varies as the condition changes.
 Pulse width modulated signals (PWM): The duty cycle of the sensor signal varies as the condition changes. The frequency of
this signal is constant.

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17
 g00288430
Illustration 1
Pulse Width Modulated Signal

Speed Sensors (Transmission, Engine, and Torque Converter Output)

g00288428
Illustration 2
Speed Sensor

There are two transmission speed sensors, one engine speed sensor, and one torque converter output speed sensor on the machine. The
speed sensors are inputs of the power train ECM. These speed sensors are frequency sensors. Frequency sensors produce a signal (Hz)
which varies as the condition changes. The sensor generates an approximate sine wave signal from the gear teeth as the gear teeth pass
the sensor. The sensor produces a signal that equals one pulse per gear tooth. This signal is sent to the power train ECM. The power
train ECM measures the frequency of the signal in order to determine the speed of the condition. The power train ECM receives
18
signals from the speed sensors. The power train ECM uses the input from the speed sensors in order to determine the speed of the
system. The power train ECM uses the input from the speed sensors in order to regulate transmission shifts. Each speed sensor has two
connections to the power train ECM (+ and -).

The power train ECM sends the speed information to other electronic control modules via the CAT Data Link. For all of the speed
sensors, connector contact 2 is the signal line and connector contact 1 is the return line. Two intermediate speed sensors (if equipped)
measure intermediate transmission speed. Two transmission speed sensors measure transmission output speed. The power train ECM
uses the pairs of speed sensors to determine the direction of rotation.

Note: The speed sensors are used to diagnose each other during normal operation. The power train ECM periodically checks the value
from the speed sensor. If an incorrect value is found, the power train ECM will log a service code that indicates a fault for a speed
sensor circuit.

Reference: For more information on diagnostic operations for the power train electronic control system, refer to Systems Operation,
"Power Train Electronic Control System" for the machine that is being serviced.

Reference: For more information on the CAT Data Link, refer to the Service Manual module Systems Operation, "CAT Data Link"
for the machine that is being serviced.

Reference: For more information on the power train electronic control module (ECM), refer to the Service Manual module Systems
Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.

Differential
SMCS - 3258
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 g00477662
Illustration 1
Typical Illustration

(1) Bevel pinion. (2) Bevel gear. (3) Ring gear. (4) Planetary gear. (5) Carrier. (6) Axle shaft. (7) Spider. (8) Differential case. (9) Pinion. (10) Side gear. (11)
Brake piston. (12) Brake disc. (13) Reaction plate. (14) Sun gear.

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A differential divides the power that is sent to the wheels or a differential causes a balance of the power that is sent to the wheels. A
differential allows one wheel to turn at a slower rate than the other wheel on an axle. For example, this occurs during a turn. During a
turn, the differential allows the inside wheel to rotate at a slower rate in relation to the outside wheel. The differential still sends the
same amount of torque to each wheel.

Straight Forward or Straight Reverse Operation

When the machine moves in a straight direction with the same amount of traction under each drive wheel, the same amount of torque
on each axle holds the pinions. When the machine moves in a straight direction the pinions do not turn on the spider.

Bevel pinion (1) turns bevel gear (2). Bevel gear (2) turns case (8). Case (8) turns spider (7). Spider (7) drives side gears (10) and
pinions (9) together. Pinions (9) do not turn on the spider. Side gears (10) turn at the same speed as bevel gear (2) and case (8). Side
gears (10) turn final drive sun gears (14). The same amount of torque is sent through the final drives to each wheel.

This provides the same effect as having both drive wheels on the same axle shaft.

Operation during a Forward Turn or Operation during a Reverse Turn

When the machine is in a turn, the outside wheel turns faster than the inside wheel.

Bevel pinion (1) turns bevel gear (2). Bevel gear (2) turns case (8). Case (8) turns spider (7). Spider (7) drives side gears (10) and
pinions (9) together. Side gears (10) turn final drive sun gears (14). Because the outside wheel turns faster than the inside wheel, the
outside side gear (10) turns pinions (9) on spider (7). As the pinions turn, the pinions move around the side gears. This allows the
outside wheel to turn faster than the inside wheel.

The same amount of torque is sent through the final drives to both the inside wheels and to the outside wheels. This torque is only
equal to the amount of torque that is necessary to turn the outside wheel.

Loss of Traction (Wheel Slippage)

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When one wheel has more traction than the other wheel, the operation of the differential is identical to the operation of the differential
during a turn. The same amount of torque is sent to both wheels. This torque is only equal to the amount of torque that is necessary to
1 1 0

turn the wheel with the least resistance.

Differential Backlash and Bearings - Adjust

SMCS - 3258-025-BKL
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Illustration 1 g00303284

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Differential and Bevel Gear

(1) Bearing sleeve

(2) Bearing cup

(3) Bearing cone

(4) Adjusting nut

(5) Bolt

(6) Bevel pinion

(7) Bearing cone

(8) Bearing cup

(9) Housing

(10) Bearing cup

(11) Bearing cone

(12) Washer

(13) Nut

(14) Intermediate housing

(15) Differential group

(16) Bevel gear

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(17) Bolt

(18) Bearing sleeve

(19) Bolt

(20) Adjusting nut

(21) Differential case

(22) Bearing cone

(23) Bearing cup

(24) Pins

(25) Pin

(26) Pin

(27) Center housing

(28) Shims

(A) Bolt circle radius

Note: The following procedure controls bearing preload. The procedure provides the same results for new bearings and for used
bearings.

1. Assemble differential group (15) .

2. Heat bevel gear (16) to 135°C (275°F) for a maximum of 4 hours. Install the bevel gear on the differential group.

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3. Install four large pins (25) partially into bevel gear (16) . Install four small pins (26) into large pins (25) . Make sure that the
serrations of the small pins are 180 degrees from the serrations of the large pins. Press pins (25) and (26) so that the pins are
flush with the surface of bevel gear (16) . Torque the 20 9X-6494 Bolts (17) to 285 ± 40 N·m (210 ± 30 lb ft) and then turn the
bolts for an additional 120 ± 5° turn. Make sure that the bevel gear is seated on the differential group shoulder.

Note: Bolts (17) cannot be substituted with other bolts. If bolts (17) are replaced, new 9X-6494 Bolts must be installed.

4. Press bearing cone (3) and bearing cone (22) on differential case (21) . Make sure that the bearing cones are fully seated.

Note: If you freeze the bearing cups, allow the parts to reach a uniform temperature. Then use a driver or a press to reset the
bearing cups. The limit for freezing the bearing cups is -29°C (-20°F). Remove any frost and wipe the bearing cups dry.
Lubricate the bearing cups with SAE 30W gear oil in order to prevent rust on the bearing cups.

Note: If you heat the bearing cones, allow the parts to reach a uniform temperature. Then use a driver or a press to reset the
bearing cones. The limit for heating the bearing cones is a maximum of 135°C (275°F) for a maximum of 4 hours. Lubricate
the bearing cones with SAE 30W gear oil after the bearing cones have cooled in order to prevent rust on the bearing cones.

5. Remove intermediate housing (14) from center housing (27) .

6. Install bearing cups (2) and (23) , bearing sleeves (1) and (18) , and two pins (24) . Lubricate the threads of adjusting nuts (4)
and (20) and install the nuts in intermediate housing (14) and in center housing (27) .

7. Position center housing (27) in an appropriate supporting fixture so that the open side faces upward. With a lifting device,
lower differential group (15) and bevel gear into position on three dowels in center housing (27) .

8. Install intermediate housing (14) on center housing (27) . Apply 1U-8846 Liquid Gasket to the contacting surfaces prior to
assembly. Torque the three bolts to 100 ± 20 N·m (75 ± 15 lb ft).

9. Lubricate the O-ring seal and install the O-ring seal on pinion housing (9) . Install pinion housing (9) on center housing (27) .
To install the front differential, torque the ten bolts to 300 ± 40 N·m (220 ± 30 lb ft). To install the rear differential, torque the
12 bolts to 300 ± 40 N·m (220 ± 30 lb ft). Use the original thickness of shims (28) or use a new shim pack that is measured to
the same thickness as the original pack. If the original shim pack is not available, use 70% of a new shim pack.

25
 Note: The needed thickness of the shim pack may change when the tooth contact pattern is adjusted.

10. Tighten adjusting nuts (4) and (20) to a position that maintains gear backlash and slight bearing end play. This position should
not maintain tight gear mesh.

11. Reposition center housing (27) in the supporting fixture so that center housing (27) and pinion housing (9) are horizontal. The
parts are horizontal when the parts are mounted in the machine.

Table 1
Required Tools
Part Number Description Quantity
1U-6690 Socket Wrench Assembly 1

12. Measure the torque that is needed to rotate pinion shaft (6) . Record this torque. For this measurement, use a 1U-6690 Socket
Wrench Assembly on pinion shaft nut (13) .

13. While you rotate pinion shaft (6) back and forth, tighten adjusting nut (20) to the zero backlash position. Then back off
adjusting nut (20) by a value of 20° plus the increment to the nearest lock position.

14. Tighten adjusting nut (4) on the bevel gear group while you are rotating the pinion shaft. Tighten nut (4) until the overall
preload rolling torque that is measured at the pinion shaft is 4.5 N·m to 6.8 N·m (40 lb in to 60 lb in).

Note: When you check for correct assembly and for correct adjustment, measure the rolling torque of the bevel gear group at
the shaft of the pinion. For new bearings, the rolling torque should be 4.5 to 6.8 N·m (40 to 60 lb in). For used bearings, the
rolling torque should be 2.25 to 3.4 N·m (20 to 30 lb in).

15. Measure the backlash between bevel gear (16) and pinion shaft (6) . Measure the backlash at the heel of the bevel gear. The
backlash must be 0.30 + 0.12 - 0.10 mm (0.012 + 0.005 - 0.004 inch). To measure the backlash, place a dial indicator tangent
to the spline. Refer to Illustration 2 for an example. Make sure that the yoke or the spline adapter is tight to the spline.

26
 g00275111
Illustration 2
Pinion Shaft Spline (backlash measurement)

(B) Distance of dial indicator from the centerline of the pinion.

16. Table 2 that follows lists examples of backlash at the pinion shaft. Table 2 shows the different distances from the centerline of
the pinion to the dial indicator.

Table 2
Examples of Backlash at Pinion Shaft
Dimension (B) Nominal Backlash Maximum Backlash Minimum Backlash

50 mm (2 inch) 0.28 mm (.011 inch) 0.40 mm (.016 inch) 0.18 mm (.007 inch)

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 100 mm (4 inch) 0.57 mm (.022 inch) 0.80 mm (.032 inch) 0.35 mm (.014 inch)

150 mm (6 inch) 0.86 mm (.034 inch) 1.20 mm (.047 inch) 0.53 mm (.021 inch)

200 mm (8 inch) 1.15 mm (.045 inch) 1.60 mm (.063 inch) 0.70 mm (.028 inch)

17. If the backlash does not meet specifications, loosen one adjusting nut and tighten the opposite adjusting nut by the same
amount. This procedure will maintain the bearing preload.

Pinion and Bevel Gear Tooth Contact Check

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 g00103470
Illustration 3

1. After the differential backlash adjustments and pinion preload adjustments have been made, tooth contact between pinion shaft
(6) and bevel gear (16) must be checked. Perform the procedure that follows:
a. Apply small amount of Prussian blue, of red lead, or of paint on three adjacent teeth or on four adjacent teeth of bevel
gear (16) .

b. Rotate pinion shaft (6) for several revolutions in one direction. Then rotate pinion shaft (6) for several revolutions in
the opposite direction. Then turn the pinion shaft in one direction until the marked teeth can be viewed.

c. The correct area of tooth contact begins near the inside end of the teeth of bevel gear (16) . The correct area reaches a
maximum of 50 percent of the tooth length. See Illustration 3 for an example of the correct area of tooth contact.

Illustration 4 g00103471

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2. If the tooth contact looks like the marks in Illustration 4, perform the procedure that follows:
a. Remove some of shims (28) .

b. From Testing and Adjusting, "Differential Backlash and Bearing - Adjust", perform Step 15, Step 16, and Step 17
again.

c. Perform Step 1 of "Pinion and Bevel Gear Tooth Contact Check" again.

g00103472
Illustration 5

3. If the tooth contact looks like the marks in Illustration 5, perform the procedure that follows:
a. Add some of shims (28) .

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 b. From Testing and Adjusting, "Differential Backlash and Bearing - Adjust", perform Step 15, Step 16, and Step 17
again.

c. Perform Step 1 of "Pinion and Bevel Gear Tooth Contact Check" again.

Note: Always make sure that the backlash adjustment is correct before an adjustment is made to the area of tooth contact. To
get the correct adjustments, the backlash and tooth contact may need adjusted several times. Always remember that a change to
gear clearance (backlash) will also change the gear contact. A change in gear contact will also change gear clearance
(backlash).

4. After adjustments are made, remove the Prussian blue, red lead or paint from the gears.

5. Install one bolt and lock (5) and (19) in each adjusting nut (4) and (20) . Tighten both bolts and bend the locks.

1 1 0

Transmission Oil Pump

SMCS - 3066
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31
32
 g00434238
Illustration 1
Torque Converter and Pump Drive Housing

(1) Torque converter housing. (2) Transmission and hydraulic pump drive gear. (3) Pump drive flange. (4) Transmission oil pump.

g00434241
Illustration 2
Location of the transmission oil pump

(4) Transmission oil pump.

Transmission oil pump (4) is mounted on the left side of torque converter housing (1) under the cab.

Transmission oil pump (4) is a positive displacement type pump. The one-section gear pump is bolted to the torque converter housing
(1). The following pumps are mounted on the transmission oil pump (4) and driven by the transmission oil pump: steering pump,
implement pump and pilot/brake pump.

The pump drive gear is fastened to the torque converter impeller. The pump drive gear drives transmission and hydraulic pump drive
gear (2). Transmission and hydraulic pump drive gear (2) is fastened to pump drive flange (3). Pump drive flange (3) is connected to
transmission oil pump (4) by splines. The splined shaft of the transmission oil pump drives the transmission oil pump.

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 g00434243
Illustration 3
Transmission oil pump

(5) Cover assembly. (6) Body assembly. (7) Manifold assembly. (8) Drive gear. (9) Gear.

34
The main components of the transmission oil pump are (5) cover assembly, (6) body assembly, (7) manifold assembly, (8) drive gear,
1 1 0

and (9) gear.

Temperature Sensor (Transmission Oil )

g00329095
Illustration 3
Transmission Oil Temperature Sensor

The transmission oil temperature sensor is a pulse width modulated sensor (PWM). The duty cycle of the sensor signal varies as the
temperature changes. The frequency of the sensor signal is constant at 5000 Hz. The power train ECM measures transmission oil
temperature with the transmission oil temperature sensor. The power train ECM uses the oil temperature reading in order to adjust the

35
shift times of the transmission. The power train ECM adjusts the shift times of the transmission in order to provide smooth shifts over
the various ranges of the transmission oil temperature.

Reference: For more information on the operation of the machine, refer to the Service Manual module Operation and Maintenance
Manual for the machine that is being serviced.

Reference: For more information on the power train electronic control module (ECM), refer to the Service Manual module Systems
Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.

Position Sensor (Left Pedal)

g00779650
Illustration 4
Position Sensor (Left Brake Pedal)

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The position sensor (left brake pedal) sends an input to the ECM. The sensor will continuously update the power train ECM on the
position of the left pedal. The left pedal position sends a change in the input signal to the power train ECM. The ECM records the
change of position. Then, the ECM activates the appropriate solenoid valve.

The position sensor (left brake pedal) is a PWM sensor. The sensor continuously generates a PWM signal. The duty cycle varies in
proportion to the position of the lever. The ECM receives the PWM signal from the position sensor. The ECM measures the duty cycle
in order to determine the position of the lever. The frequency of the sensor signal is constant at 5000 Hz. The machine electrical
1 1 0

system provides +battery voltage to the lever position sensor for operating power.

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