Product Support Program For Updating The Transmission Control Valves On Certain 768C Tractors And 769C Trucks Caterpillar

NOTE: The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.

NOTE: This Program can be administered either before or after a failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS4744" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and use "T" as the SIMS Description Code. If administered after failure, use "96" as the Warranty Claim Description Code and use "Z" as the SIMS Description Code.

NOTE: This Revised Service Letter replaces the April 18, 1992 Service Letter. Changes have been made to the Affected Product, Parts Needed, Action Required, and Rework Procedure.

NOTE: The transmission controls can be updated when removed from the Affected Product for a transmission rebuild until April 30, 1995. However, this Program can only be implemented to update the transmission while in the Affected Product until April 30, 1993.

Termination Date

Problem

Slow transmission control modulation, due to the effects of cold oil, on some control stations, may result in excessive clutch slippage. Damage may occure to the discs and plates in the transmissions of certain 768C Tractors and 769C Trucks.

Affected Product
Model & Identification Number

768C (02X350-370)

769C (01X2877-5960)

Transmissions with S/N 8KA3532 and up do not require this rework. Factory reworked transmissions will be stamped with the letter "J" on the transmission case next to the S/N Plate. These transmissions will have a S/N below 8KA3532.

Parts Needed

1 - 7G1594 Gasket

1 - 8P9737 Orifice

1 - 3T1437 Piston

1 - 8T1639 Gasket Kit

3 - 6T2293 Piston

1 - 7T0570 Spring

1 - 7T0571 Spring

2 - 6V5341 Pin-Spring

1 - 6V8235 Pin-Spring

4 - 9W7411 Spring

2 - 9W7412 Spring

NOTE: One of the 3T1437 Pistons being removed from station a, c, or f should be used if it meets reuse guidelines (SEBF8134).

NOTE: Additional shims may be required for adjusting initial pressures.

Action Required

The rework consists of changes to two transmission control components:

Part 1 This part of the update consists of modification to the 3T9583 Rotary Selector Spool in the 7G1365 Selector And Pressure Control Valve Group. Removal of the drain orifices in the selector spool will require the use of a drill press and carbide drill. After all modifications have been completed, the 7G1365 Pressure Control Group must be identified as a 9U9030 Pressure Control Group. See Illustration 1.

Part 2 This part of the update consists of various spring, orifice, and piston changes to all seven ICM stations in the 7G1366 Pressure Control Group. See Illustration 2. After all modifications have been completed, the 7G1366 Pressure Control Group must be identified as a 9U9028 Pressure Control Group.

If this update is performed with the transmission installed, the drive shaft must be disconnected or the axle shafts removed for the checking and adjustment of the initial pressures.

See the attached procedure.

Service Claim Allowances

Update Transmission Controls When Removed From Affected Product For Transmission Rebuild

NOTE: This is a 1-hour job to modify the rotary selector spool. No other labor will be allowed during a transmission rebuild.

Update Transmission In Affected Product

NOTE: This is a 5-hour job.

NOTE: This portion of the Program can only be claimed until 1 year after published.

Parts Disposition

Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.

Attach. (1-Rework Procedure)

Rework Procedure

Part 1 Modification To The 7G1365 Selector And Pressure Control Valve Group

...Drill out all of the drain orifices in the 3T9583 Rotary Selector Spool. Do not drill out any other orifices other than the drain orifices. See Illustration 1.

Part 2 Modification To The 7G1366 Pressure Control Group.

NOTE: All initial pressures are +50i -35 kPa (+7 -5 psi). All final pressures are +240 -100 kPa (+35 -15 psi).

...The following control stations are to be modified as outlined below. See Illustrations 2 and 3.

A. Station "A" for No. 3 Clutch

1. Remove the 9W7410 Outer Spring (Blue) and add a 9W7411 Outer Spring (Yellow).

2. Remove the 3T1437 Load Piston and add a 6T2293 Load Piston.

3. Set the initial pressure at 515 kPa (75 psi) [approximately 4.14 mm (.163 ") of shims]. This should produce a final pressure of 1690 kPa (245 psi).

B. Station "B" for No. 1 Clutch:

1. Add a 7T0571 Inner Spring (Green)

2. Remove the 8P9738 Orifice [4.58 mm (.18 ") thick] and add an 8P9737 Orifice [2.54 mm (.10") thick].

3. Set the initial pressure at 345 kPa (50 psi) (approximately 3.78 mm (.147 ") of shims]. This should produce a final pressure of 2035 kPa (295 psi).

C. Station "C" for No. 2 Clutch:

1. Remove the 9W7411 Outer Spring (Yellow) and add a 9W7412 Outer Spring (Green).

2. Remove the 3T1437 Load Piston and install a 6T2293 Load Piston.

3. Set the initial pressure at 380 kPa (55 psi) [approximately 4.42 mm (.174 ") of shims]. This should produce a final pressure of 1895 kPa (275 psi).

D. Station "E" for No. 5 Clutch:

1. Remove the 9W7410 Outer Spring (Blue) and add a 9W7412 Outer Spring (Green).

2. Remove the 7G5453 Inner Spring (Yellow) and add a 7T0570 Inner Spring (Orange).

3. Remove the 9P0687 Load Piston and install a 3T1437 Load Piston.

4. Set the initial pressure at 380 kPa (55 psi) [approximately 4.90 mm (193 ") of shims]. This should produce a final pressure of 2015 kPa (292 psi).

E. Station "F" for No. 4 Clutch:

1. Remove the 9W7410 Outer Spring (Blue) and add a 9W7411 Outer Spring (Yellow).

2. Remove the 3T1437 Load Piston and install a 6T2293 Load Piston.

3. Set the initial pressure at 380 kPa (55 psi) [approximately 3.05 mm (120 ") of shims]. This should produce a final pressure of 1425 kPa (207 psi).

F. Station "G" for No. 6 Clutch:

1. Remove the 9W7410 Outer Spring (Blue) and add a 9W7411 Outer Spring (Yellow).

2. Set the initial pressure at 345 kPa (50 psi) [approximately 2.69 mm (.106 ") of shims]. This should produce a final pressure of 2930 kPa (425 psi).

G. Station "H" for No. 7 Clutch:

1. Remove the 9W7410 Outer Spring (Blue) and add a 9W7411 Outer Spring (Yellow).

2. Set the initial pressure at 345 kPa (50 psi) [approximately 2.69 mm (.106 ") of shims]. This should produce a final pressure of 2930 kPa (425 psi).

NOTE: If this update is performed with the transmission installed, the drive shaft must be disconnected or the axle shafts removed for the checking and adjustment of the initial pressures.

Illustration 1 - 7G1365 Selector Group

Drain orifices to be removed (drilled out) in the 3T9583 Selector Spool Assembly are located in "Area 1" as shown. Eleven of the drains have orifices and all need to be removed. A carbide drill will have to be used. Depending on availability, the drill sizes that can be used are .125 ", .156", or 3.5 mm. Insure that the drill does not touch the O.D. of the drain resulting in a burr on the O.D. of the spool. Also, insure that all other burrs or chips are removed and that the spool is thoroughly cleaned after the drain orifice removal is complete. With care, this drilling operation can be done using a generic drill press and supporting "V" blocks.

Illustration 2 - Control Station Detail

Illustration III

769C Transmission Control Group (Changing from 7G1366 to 9U9028)

NOTE: There is no adjustment for maximum pressure. Adjust for primary pressure. If maximum pressure is out of specification with correct initial pressure, check the stations for correct load piston and correct spring(s). Also check spring(s) for correct spring rate.