Harsh Shifting Caterpillar

Harsh Shifting

Usage:

TRACK-TYPE TRACTORSD5M (6GN, 5ES, 6AS, 3CR, 7LR),
D6M (3WN, 4JN, 5NR, 6LR, 4HS) TRACK-TYPE TRACTORS

Problem:

Several reports of harsh shifting have been received. These occurrences have been traced to three main areas of concern.

The first area is instability during speed shifts in FORWARD. The forward direction clutch (clutch 2) pressure becomes unstable when dropped from engagement pressure to HOLD pressure [2205 kpa (320 psi) to 140 kpa (20 psi)]. This results in a shuddering or chattering during speed shifts (1F to 2F, 2F to 3F, 3F to 2F, etc). The problem is generally worse when the tractor is pushing a load.

The second area is clutch 5 (1st speed clutch) filling early, which seems to be more evident at LOW idle. During fill calibration, the values are set too high. For shifts into 1st gear in normal operation, the high calibration value tries to lock up clutch 5 before the offgoing clutches release. If this happens, clutch 5 acts as a brake and creates an audible bang and perhaps a pronounced shift shock that can be felt, as well. Many times this occurs in conjunction with an E25 error code - Calibration Value At a Limit for Clutch 5.

The last area is brake drag during LOW idle 2 to 1 shifts. While filling the rotating clutch, the system pressure drops more than it does when filling stationary clutches. If the system pressure drops below 1400 kpa (203 psi) during a shift, the brakes are in danger of touching up. This can be related to the second area of concern, above. The faster the clutch fills, the more system pressure will drop.

Solution:

All three of the previous situations require different actions to resolve. Perform the solution that relates to the corresponding situation, above. While performing every solution stated herein will not cause any harm, all procedures may not be necessary.

For unstable pressures during FORWARD speed shifts, install the lastest version of software (170-8515). The new software will ramp down the direction clutch pressure during speed shifts, preventing the pressure from becoming unstable. If the symptoms persist after the new software is installed, then replace the valve for clutch 2.

For early filling of clutch 5, run the calibration with engine speed set to 1600 RPM. By calibrating at slower speeds, there is less leakage in clutch 5 and the calibration value is lower. This creates slower filling of the clutch during normal operation and lowers clutch fill spikes for clutch 5.

For brake drag during LOW idle 2 to 1 shifts, run the fill calibration at 1600 RPM in order to slow the filling of clutch 5 (1st speed clutch).

If the brakes continue to touch up during these shifts, there is currently no other solution. The only other possibilities for rectifying the situation are to raise the idle or decelerator speed in order to provide more flow.

Be aware that these are not the only possibilities for causing harsh shifting. Other components that can effect shift quality should be checked for proper operation, as well.