Ok , I have a 1999 Expedition XLT A4WD/4H/4L . After I got it I found the front drive shaft was gone . I got one and put it in , the 4WD did not work . I got a shift motor and the 4WD now works . My problem in 4H or 4L at low speed it is ok , you give it gas it crackles and pops . If you turn...