TSB: Transit Drivetrain

Some 2016-2024 Ford Transit vehicles equipped with single rear wheel drive with U-joints at the transmission flange and rear driveshaft may experience a boom/hum/moan noise from the rear while driving, most noticeable at highway speeds:
70-75 mph for 4.10 axle ratio
75-80 mph for 3.73 axle ratio
85-90 mph for 3.31 axle ratio

This may be due to a second-order driveline frequency transmitted through the driveshaft, rear axle and into the body through the leaf springs. 

• Inspect the driveshaft, driveshaft U-joints, driveshaft center bearing(s) and slip yoke splines for damage or wear and service as needed.
• Using the Mastertech Series MTS 400 driveline balance and NVH analyzer (or equivalent), analyze the noise. Does this identify the concern as a driveline vibration? If yes, refer to workshop manual section 205-01 to resolve and re-test. If no, mark the pinion flange and rear driveshaft U-joint to enable correct indexing of the driveshaft during installation.
• Remove the driveshaft to axle pinion flange bolts. Clean the bolts of old Loctite. With a suitable strap, support the driveshaft to avoid any undue stress to the driveshaft-to-transmission output flange U-joint or driveshaft center bearing. 
• Inspect the pinion flange to driveshaft mating surfaces. Clean and remove any debris or rust.
• Install the new driveshaft torsional damper (P/N LK4Z-4A263-C) onto the axle pinion flange.
• Align the index marks and reinstall the driveshaft.
• Apply Loctite 263 to the four cleaned bolts, install the torque to 85 ft-lb. 

The torsional damper may come with a shield. If so, discard the shield.