Introduction

NOTE: For Specifications with illustrations, make reference to SPECIFICATIONS FOR 768C TRACTOR & 769C TRUCK POWER TRAIN, Form No. SENR7807. If the Specifications in Form SENR7807 are not the same as in the Systems Operation and the Testing and Adjusting, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

Troubleshooting

Use this as a reference for the location and correction of problems in the power train. When more checks are needed, use the 5P6225 Transmission Hydraulic Test Group and the 5P5224 Pressure Gauge Kit. Locations of the pressure taps and procedures for tests and adjustments are given in the 768C TRACTOR and 769C TRUCK POWER SHIFT TRANSMISSION TESTING AND ADJUSTING, Form SENR7809.

Always make visual checks first. Then check the operation of the machine and go on to check with the instruments.

Visual Checks

1. Check the oil level in the transmission and differential.

2. Check all oil lines, hoses and connections for leaks or damage. Look for oil on the ground under the machine.

3. Check wiring harness for the manual switch, slave switch and the solenoids for loose or broken connections.

4. Remove and check the transmission and torque converter oil filter elements for foreign material. Check the magnetic screen on the transfer gear case.

a. Aluminum particles give the indication of torque converter failure.

b. Bronze particles give the indication of a clutch failure.

c. Rubber particles give the indication of rubber seal or hose failure.

d. Shiny steel particles give the indication of pump failure.

e. Iron or steel chips give the indication of broken components in transmission, differential or transfer gears.

If you find bronze, rubber, aluminum, iron or steel particles, all components of the hydraulic system must be washed clean. Do not use parts with damage. Use new parts.

Checks During Operation

Operate the machine in each direction and in all speeds. Make note of all noises that are not normal and find their sources. If the operation is not correct, make a reference to the CHECK LIST DURING OPERATION for "problems" and "probable causes".

Check List During Operation

Problem: Transmission gets hot.

PROBABLE CAUSE:

1. Bad oil temperature gauge.

2. Low oil level.

3. High oil level.

4. Operation of inlet relief valve for torque converter not correct.

5. Restrictions in the core of the oil cooler.

6. Clutches do not release all the way (drag).

7. Low oil flow as a result of pump wear.

8. Magnetic screen not completely open.

9. Long periods of operation with converter at or near stall speeds.

10. Failure in scavenge pump.

Problem: Transmission selector lever does not make a shift.

PROBABLE CAUSE:

1. Adjustment of control linkage not correct.

2. Control linkage damaged.

3. Clutch did not release.

4. Operation of transmission electrical controls not correct.

Problem: Transmission shifts slowly.

PROBABLE CAUSE:

1. Low oil pressure.

2. Adjustment of control linkage not correct.

3. Operation of shift pressure valve not correct.

4. Operation of sequence and pressure control valve not correct.

5. Air leaks on inlet side of pump.

6. Operation of load piston or protective, check and flow control valves not correct.

Problem: Clutches engage very suddenly (rough shifting).

PROBABLE CAUSE:

1. Adjustment of control linkage not correct.

2. Setting of the modulation relief valve not correct.

3. Operation of check, protective or flow control valves not correct.

4. Valve springs are weak or have damage.

5. Failure in torque converter.

Problem: Transmission does not operate in any speed or does not engage (slips) in all speeds.

PROBABLE CAUSE:

1. Low oil pressure caused by:

a. Low oil level.

b. Control linkage loose or adjustment not correct.

c. Failure of the oil pump or oil pump drive.

d. Air leaks on inlet side of pump.

e. Leakage inside transmission.

f. Adjustment of the modulation relief valve not correct, or valve does not close.

g. Flow control valve does not close.

h. Load piston does not move.

2. Mechanical failure in transmission.

3. Automatic selector valve not in operation.

4. Failure in torque converter.

5. Failure of the differential or the final drives.

6. Failure of the transmission electrical controls.

Problem: Machine moves in Neutral.

PROBABLE CAUSE:

1. Adjustment of control linkage not correct.

a. Transmission electrical controls have a defect.

2. No. 1, No. 2 or No.3 clutches partially engaged.

Problem: Transmission engages but the machine does not move.

PROBABLE CAUSE:

1. Differential has broken parts and will not turn.

2. Failure in final drives.

3. Too many clutches are engaged in the transmission.

4. Failure in the transmission.

5. Parking brakes do not release.

6. Rear drive shaft broken.

Problem: Transmission does not operate in Reverse.

PROBABLE CAUSE:

1. Low oil pressure to the torque converter.

2. No. 7 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

3. Failure in the transmission neutralizer.

Problem: Transmission does not operate in First, Second and Third speeds.

PROBABLE CAUSE:

1. No. 6 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

Problem: Transmission does not operate in Fourth and Fifth speeds.

PROBABLE CAUSE:

1. No. 5 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

Problem: Transmission does not operate in Sixth and Seventh speeds.

PROBABLE CAUSE:

1. No. 4 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

Problem: Transmission does not operate in Second, Fourth and Sixth speeds.

PROBABLE CAUSE:

1. No. 3 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

Problem: Transmission does not operate in Third, Fifth and Seventh speeds.

PROBABLE CAUSE:

1. No. 2 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too much wear.

c. Clutch has parts that are broken.

Problem: Transmission does not operate in Reverse and First speeds.

PROBABLE CAUSE:

1. Torque converter failure.

2. No. 1 clutch not engaged (slips) because of:

a. Low oil pressure.

b. Discs and plates have too wear.

c. Clutch has parts that are broken.

Problem: Transmission makes shifts rapidly (hunts).

PROBABLE CAUSE:

1. Operation of governor cut-off valve not correct.

2. Bad friction between wheels and ground.

3. Operation of shift governor not correct.

4. Shift points out of adjustment.

Problem: Transmission does not make a shift.

PROBABLE CAUSE:

1. Low oil pressure.

2. Shift points out of adjustment.

3. Operation of governor cut-off valve not correct.

4. Operation of hold valve not correct.

5. Operation of shift governor not correct.

6. Transmission controls held by detents, valve spools or linkage.

7. Wiring harness or electrical switches have a defect.

Problem: Transmission does not make a shift up or down.

PROBABLE CAUSE:

1. Low oil pressure.

2. Shift points out of adjustment.

3. Operation of shift governor not correct.

4. Operation of hold valve not correct.

5. Control linkage broken or out of adjustment.

6. Automatic selector spool cannot move.

7. Shift solenoids have a defect.

Problem: Transmission shifts up or down at wrong time.

PROBABLE CAUSE:

1. Control linkage broken or out of adjustment.

2. Shift points out of adjustment.

3. Operation of shift governor not correct.

4. Pressure reduction valves not moving and giving very low or no reference pressure.

5. Transmission electrical controls (switches) have a defect.

Problem: Transmission goes beyond a speed without stopping in that speed and will not shift down lower than a specific speed.

PROBABLE CAUSE:

1. Automatic selector spool will not move out of its bore in the valve body.

2. Reference pressure too high.

Problem: Transmission will not make a shift down beyond a specific speed but makes a shift up normally beyond that same specific speed.

PROBABLE CAUSE:

1. Automatic selector spool will not move to the inside of the valve body.

2. Operation of shift governor not correct.

Problem: Transmission operation, with hot oil, is not smooth.

PROBABLE CAUSE:

1. Bolts in valve body not tightened correctly, which causes the parts of the body not to fit or operate.

2. Torque converter not in operation during shifts.

Problem: Torque converter gets hot.

PROBABLE CAUSE:

1. Bad temperature gauge.

2. Mechanical failure of torque converter.

3. Too much oil leakage in torque converter.

4. Not enough oil to torque converter because of:

a. Oil pump failure.

b. Too much oil leakage into transmission.

c. Operation of inlet relief valve not correct.

5. Too much restriction in oil cooler or oil lines.

6. Too much operation of machine at or near stall speed.

7. Too much oil in torque converter because of:

a. Failure in scavenge pump.

b. Flow of oil through screen assembly is stopped.

Problem: Pump noise not normal.

PROBABLE CAUSE:

1. Loud sounds at short intervals, that give an indication that particles are in the pump, are caused by pump cavitation.

2. A constant loud noise is an indication of pump failure.

3. Air at the inlet side of the pump (aeration).

Nospin Differential

Nospin Differential Test - (Before Installation)

After the NOSPIN differential has been assembled and before it is installed in the machine, make a test of the operation of the differential as follows:

1. Install the NOSPIN differential in the case.

2. Put the case in a stand or a vise to keep it from rotation.

3. Install both axles in the case.

TEST PROCEDURE FOR NOSPIN DIFFERENTIAL
1. Case. A. Axle. B. Axle.

4. Put a force in a clockwise direction on both axles.

5. Keep the force on axle (A) and turn axle (B) in a counterclockwise direction. A small noise will be heard in the NOSPIN differential and axle (B) will turn freely.

NOTE: Make sure the force is kept on axle (A).

6. Keep the force on axle (A) and turn axle (B) in a clockwise direction. A small noise will be heard in the NOSPIN differential and axle (B) will not turn any further.

NOSPIN DIFFERENTIAL TEST

7. Put a force in a counterclockwise direction on both axles.

8. Keep the force on axle (A) and turn axle (B) in a clockwise direction. A small noise will be heard in the NOSPIN differential and axle (B) will turn freely.

NOTE: Make sure the force is kept on axle (A).

9. Keep the force on axle (A) and turn axle (B) in a counterclockwise direction. A small noise will be heard in the NOSPIN differential and axle (B) will not turn any farther.

10. Do Steps 4 through 9 again, except now hold axle (B) and turn axle (A).

If the NOSPIN differential does not have the correct action, inspect the components and check the assembly procedure.