768C TRACTOR & 769C TRUCK POWER TRAIN: Troubleshooting Part 1

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.

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768C TRACTOR & 769C TRUCK POWER TRAIN: Troubleshooting Part 1 2013-02-05T11:14:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown