1990/01/08 Caterpillar

621E, 623E, 631E, 637E, 651E, 657E, 768C ( 2X350-Up ),
772B ( 64W168-Up ),
776 ( 14H206-Up ),
776B Tractors;
769C ( 1X2877-Up ),
773B ( 63W1221-Up ),
777 ( 84A1284-Up ),
777B, 785, 789 Trucks

Reference: Service Magazine; August 7, 1989; Page 9; "New Transmission Control Switch Used In Transmission Hydraulic Controls." Service Magazine; September 4, 1989; Page 4; "New Switch Drive Coupling Assembly Used In Transmission Hydraulic Controls." Service Magazine; October 9, 1989; Page 3; "Extension Cable Makes It Easier To Use ICM Transmission Control Monitor."

Reference: Special Instruction, SEHS7918, "Service Information And Use Of 6V4050 Transmission Shift Analyzer."

Erratic shifting of the ICM transmissions in the above models has been a random problem. The problem can be caused by incorrect phasing (angular relationship) between the detent cam on the rotary selector spool and the actual gear switch in the transmission hydraulic control group.

Incorrect switch phasing has been primarily related to two areas. One area was angular inaccuracies in the coupling between the switch and the rotary spool (see Illustration 1). This problem has been corrected by changes incorporated in the new 6Y9849 and 6Y9850 Coupling Assemblies and the new 9W1409 Actual Gear Switch (see Reference Articles). A second problem area has been incorrect location of the 9W7008 Rotary Selector Spool Detent Spring Assemblies with respect to the 8P9740 Detent Cam on the selector spool (Illustration 2).

Illustration 1. Transmission hydraulic controls.

Illustration 2. Rotary selector spool detent spring assemblies and detent cam.

To obtain correct phasing between the selector spool and the range switch, it is essential that the 9W7011 Pins in BOTH of the detent spring assemblies be seated on the detent cam teeth as shown in Illustration 3A. Incorrect switch phasing and erratic shifting will result if the pins are not seated correctly (see examples in Illustrations 3B and 3C).

Illustration 3. Location of 9W7011 Pins (part of 9W7008 Spring Assembly) on 8P9740 Detent Cam.

To achieve correct seating of the pins, it is necessary to use the following assembly/adjustment procedure.

1. Assemble the 6T4308 Support Assembly on the selector valve body. Tighten retaining bolts to a low torque.

2. Assemble the 9W7008 Detent Spring Assemblies on the support assembly. Tighten retaining bolts to 30 ± 7 N·m (22 ± 5 lb ft).

3. Loosen the support assembly 4B3388 Bolts ONLY approximately 1/8 turn. The support assembly is increasingly "cocked" with respect to the mounting face on the valve body by the relief valve spring force as the bolts are backed out further. This causes an increase in the force required to move the support assembly across the valve body face. Free movement of the support assembly is required to correctly seat the detent pins.

4. Using a .25" (1/4") square drive extension in the end of the detent cam, repeatedly rotate the cam slightly clockwise and counterclockwise within one detent cam tooth space. This will cause the detent spring support assembly to move on the valve body face and assume a position where both of the detent pins will be correctly seated in the cam notches (see Illustration 3A). Visual observation of the movement of the ends of the springs and the detent pins while "rocking" the cam will indicate when the pins are correctly seated.

Illustration 4. Method to rotate transmission rotary selector spool.

If the spring support assembly will not move sufficiently to allow seating of BOTH detent pins, it may be necessary to (1) change springs because one or both may not be the correct length, or (2) to modify the bolt holes and the bolt seat spotfaces on the spring support assembly.

An improved 6T4308 Support Assembly (same part number) is in production with elongated bolt holes and larger spotfaces to allow increased movement of the bolts in the holes and bolt seat washers on the spotfaced surfaces. Illustration 5 includes dimensions for reworking the earlier support assembly to the latest configuration.

Illustration 5. Dimensions for modifying earlier 6T4308 Support Assembly.

5. When the detent pins are correctly seated, tighten the spring support retaining bolts to 30 ± 7 N·m (22 ± 5 lb ft). Again, rotate the cam slightly clockwise and counterclockwise to determine that both detent pins move OUTWARD simultaneously when the cam is rotated in either direction.

Following installation of the complete hydraulic control group (including solenoid manifold and range switch) in the transmission, one further step should be taken to determine if phasing of the actual gear switch is correct. This can be accomplished as follows.

Test Procedure With Transmission Not Installed In Vehicle

1. Install the 6V4050 Transmission Shift Analyzer according to reference Special Instruction. The cable connections to the shift solenoids do not need to be made. Turn the test-mode switch to the 4/8 SPD - Sync Switches position. The gear selector switch can be placed in any gear position from 1-up.

2. As shown in Illustration 4, install an extension .25" (1/4") square drive in the end of the rotary selector spool detent cam.

3. Starting with the first gear position, slowly rotate the cam in both counterclockwise and clockwise directions from the center of the notch on the cam until the actual gear switch contact disengages, causing the letter "E" to appear on the analyzer display. The degree of cam rotation to the point of switch contact opening should be approximately the same on both directions from center, if switch timing is correct. This check should also be made in a mid-range position of the detent cam and rotary spool.

Test Procedure With Transmission Installed In Vehicle

The procedure with the transmission installed is the same as the "Test Procedure With Transmission Not Installed In Vehicle" with one exception. As explained, the 6V4050 Shift Analyzer can be used to detect actual gear switch contact opening; however, with the transmission installed, the transmission electronic switching control group in the vehicle can also be used for this purpose. When the electronic control is used, actual gear switch contact opening is indicated when the actual gear indicator lights, for the gear position in which the detent cam has been placed, are extinguished. The use of a 4C4068 Extension Cable Assembly will enable the control box to be moved to a position where the control box can be viewed by the person conducting the test (see Reference Articles).

If the detent springs have been correctly assembled and the overall switch phasing checks indicate that phasing is still in error, it will be necessary to check several other areas to determine the cause. These areas are as follows.

1. The pin(s) which retain the detent cam on the rotary selector spool assembly could be partially sheared, resulting in angular displacement of the cam on the spool.

2. The 9P9650 Switch Coupling Drive Dowel in the rotary selector spool assembly could be damaged.

3. There could be miscellaneous problems associated with the earlier actual gear switch couplings. Installation of the current 6Y9849 or 6Y9850 Coupling Assemblies along with the current 6Y1409 Switch will eliminate this problem area.

4. Incorrect fit between the switch coupling shaft and the "D" section drive hole in the switch rotor. This problem will also be corrected with installation of the current coupling and switch.