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This knocking sound is most like coming from two places, the ujoints on the front driveshaft or the stabilizer bar links. Let me know if this may be the case.
There is an actual Ford Technical Service Bulletin related to this issue. See below.
DRIVELINE CLUNK/GRUNT OR SHUDDER DURING ACCELERATION AND/OR BRAKING
TECHNICAL SERVICE BULLETIN
Reference Number(s): 04-1-6, Date of Issue: January 26, 2004
NOISE - DRIVELINE CLUNKING/GRUNTING NOISE OR SHUDDER SENSATION DURING LIGHT TO MODERATE ACCELERATION AND/OR BRAKING
TRANSMISSION - DRIVELINE CLUNKING/GRUNTING NOISE OR SHUDDER SENSATION DURING LIGHT TO MODERATE ACCELERATION AND/OR BRAKING
Some 1998-2004 F-150 4X4 vehicles with a one piece drive shaft may exhibit a clunking or grunting noise and/or a shudder sensation from the driveline. The condition will typically occur during light to moderate acceleration from a stop and/or braking. This may be caused by the slip yoke not sliding smoothly on the transfer case output shaft splines.
To service, lubricate the slip yoke with Teflon Grease (D2AZ-19590-A). Refer to the following Service Procedure.
- Road test the vehicle to verify the condition.
- Remove the driveshaft per Section 205-01 of the Workshop Manual.
NOTE: INDEX (MARK) THE DRIVESHAFT YOKE TO AXLE FLANGE FOR REASSEMBLY.
- Lubricate the slip yoke with 7-13 grams (0.25-0.46 oz.) of Teflon Grease (D2AZ-19590-A).
- Re-index and reinstall the driveshaft per Workshop Manual.
- Check the transfer case fluid level and add MERCON Automatic Transmission Fluid XT-2-QDX if necessary.
- Road test to verify the condition is corrected.
Part NumberPart Name
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage.
040106ALubricate The Slip Yoke With Teflon Grease Vehicles With One-Piece Driveshaft (Includes Time To Remove And Install Driveshaft)1.0 Hr.
Basic Part No.Condition Code