F250 4WD Intermittent Not Locking In

[jgerber]

2002 F-250 not locking in on auto. Already replaced vacuum actuator and dash switch. ???????

 

[bowtiehatr]

ok put a vacuum gauge on each line where it attaches to the hub to check for proper vacuum. 15 inches minimun is where i would say it should be. you could have bad seals in the spindle(s)

 

[blacksnapon]

Yeah, I have been replacing the large seal next to the u-joint. You get debris between the axle and seal, and that causes a loss of vacuum. If you can somehow put no more than 2 or 3 psi of pressure (I use an evap tester) you can spray soapy water on each seal and o-ring (the o-rings are in the lockouts) look for the bubbles.