Transfer Case Noise HeardTypically Between 20 and 40 MPH- keywords chug coast tick

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some customers may comment about transfer case noise on this application. The noise may be concentrated in the front of the transfer case. The noise may be described as a tick, chug or whoosh. The noise is generally heard between 20-40 mph and can be heard in both 4Hi Open and 4Hi Lock. Most often the event is heard in a coast condition, on a smooth road, with all accessories off.

Dimensional variation in the planetary carrier assembly may contribute to this concern. Drive the vehicle up to 40 mph and coast down to 20 mph. Technicians may also want to maintain a steady-state speed with light throttle

The frequency of the noise will track with vehicle speed.

The noise event occurs approximately:

4 times/second at 20 mph

6 times/second at 30 mph

8 times/second at 40 mph

The noise level may vary with speed. Noise may be heard at all speeds 20-40 mph or only at distinct speeds from 20-40 mph.

Transfer Case Neutral Test

1. Shift Vehicle transmission into Neutral.
2. Shift Transfer Case into Neutral.
3. Press and hold 4Hi Open and 4Lo Lock buttons simultaneously for several seconds until Red Neutral indicator lights.
4. Shift Vehicle transmission into Drive.
5. Listen for tick, chug, whoosh noise at engine idle.
6. Lightly add throttle to steady-state 1500 rpm. Evaluate noise.
7. Shift Vehicle transmission into Neutral.
8. Ignition Off.
9. Ignition On engine off shift Transfer Case into 4Hi.

If the noise can be duplicated per the above diagnosis Replace the transfer case high/low planetary carrier assembly item 203 (eSI document 1550095). IT IS NOT NECESSARY TO REPLACE THE ENTIRE TRANSFER CASE FOR THIS CONCERN. Additional process changes have been put in place for the planetary gear set to address this concern. Planetary sets with the most current changes will be identified with a dot of green paint AND an OK mark stamped in ink on the output side of the gear set. BOTH marks need to be present to identify latest parts. Reference P/N 89059555.

These changes were in effect for transfer cases built 02/06/07. This would be vehicles built approximately 2/15/07. The service technician should check build dates prior to repair. The transfer case build date and type is on a self adhesive sticker that faces the bottom of the rear case half. This should be visible with the truck on a hoist.

Important:  during assembly the planetary differential gears are timed to the sun gears items 230, 231 and 233 (eSI document 1550095). This is the planetary gear set located in the rear of the transfer case. If the gears are not timed properly, the differential will not rotate without binding.

With the rear side of the planetary differential facing up, align the marks on the pinion gears. Position the alignment marks with an area on the planetary differential that can be referenced for all gears.

Reference SI Document #1550087 Steps 34 and 35 for this timing procedure

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.