Re: TSB 03-6-4 (or #17632)
Some 2003 Expedition/Navigator 4X4 vehicles may exhibit a front axle groan or hum, and/or a slight vibration, when operated in the 2 High mode. This condition is most noticeable on deceleration between 45 and 15 mph, and is not present in A4WD or 4 High. This may be due to the front halfshafts rotating at different speeds when the vehicle is operated in 2 High.
To service, install S-spring (clutch spring) into the front axle differential, causing the front halfshafts to rotate at the same speed in 2 High mode. Refer to the following Service Procedure for details.