Transfer Case NVH Issue During Coast Down

A transfer case noise, vibration and harness (NVH) concern may be found on some 2020 Silverado 2500HD/3500HD and Sierra 2500HD/3500HD models equipped transfer cases RPO NQF (Electric Shift Cont, Two Speed Transfer Case) or NQH (Active, Two Speed, Switch Activated Transfer Case). In some instances, a clunk sound may be heard during a coast-down event.

The NVH condition may be the result of a misalignment between the transmission output shaft and the transfer case input. (Fig. 15) The misalignment could cause the transfer case shift collar to slip out of engagement.

 

Fig. 15

 

If these conditions are evident, road test the vehicle up to 40 mph (64 km/h) on a smooth, flat road. Allow the vehicle to coast in Drive to below 10 mph (16 km/h), without using the brakes, and listen and feel for any bumps or clunk sounds from under the vehicle. Repeat these steps at least eight times in order to verify the condition.

If the sound is verified to be from the transfer case, the transmission output shaft may be misaligned. It will be necessary to disconnect and reconnect the transfer case to the transmission.

 

Misalignment Correction

Remove the three transmission mount nuts, the rubber hose from the transmission crossmember, and the transmission crossmember. Also remove the transmission mount from the transmission and discard the mount bolts.

Loosen all 12 transfer case bolts, but do not remove the bolts. It may be helpful to use a screw jack to raise and lower the transmission for better access to all of the bolts.

With the bolts loosened, slide the transfer case rearward so there is a minimum gap of 1/2 inch (13 mm), but not more than 1 inch (25 mm). (Fig. 16) Next, slide the transfer case forward until it is contacting the transmission again.

 

Fig. 16

 

Tighten the 12 transfer case bolts in the following sequence. Torque the bolts to 41 lb.-ft. (55 Nm). (Fig. 17)

 

Fig. 17

 

TIP: When tightening bolts 10, 11, and 12 in the sequence, remove the bolts and clean the threads on each bolt and in the transmission with brake cleaner, and then blow out the hole with compressed air to ensure there is no fluid left in it. Failure to do this may lead to stripped threads.

Be sure to use two new bolts when installing the transmission mount on the transmission.

Reinstall the transmission mount nuts and the rubber hose to the transmission crossmember.

Refer to Bulletin #19-NA-216 for additional information.

 

– Thanks to Kevin Minor

Engine Air Leak from PCV Tube
UPDATE: Rattle Sound near Front of Engine

Leave a Reply

Your email address will not be published. Required fields are marked *

*