Ford 2003 Mustang Workshop Manual page 2866

37. Lift up the mainshaft, then remove the countershaft.
38. Remove the mainshaft and shift rail as an assembly. Separate the shift rail assembly from the
mainshaft on the work bench.
39. Remove the input shaft and fourth gear synchronizer blocking ring.
40. Remove the countershaft bearing cup and the countershaft shim.
Inspect the cup for wear or damage. Install a new cup and bearing as necessary.
Inspect the cup bore for wear, scratches or grooves. Install a new transmission adapter
plate as necessary.