Ford 2003 Mustang Workshop Manual page 277

If the marks are on opposite sides of the driveshaft, the yoke or pinion flange is responsible for the
vibration.
When installing a new pinion flange, the driveshaft runout must not exceed 0.89 mm (0.035 inch).
When runout is within limits, recheck for vibration at road speed. If vibration persists, balance the
driveshaft.
7. To balance the driveshaft, install one or two hose clamps on the driveshaft, near the rear.
Position of the hose clamp head(s) can be determined by trial-and-error.
8. Mark the rear of the driveshaft into four approximately equal sectors and number the marks 1
through 4. Install a hose clamp on the driveshaft with its head at position No. 1.
Check for vibration at road speed. Recheck with the clamp at each of the other positions to find the
position that shows minimum vibration. If two adjacent positions show equal improvement, position the
clamp head between them.
9. If the vibration persists, add a second clamp at the same position and recheck for vibration.