Ford Tech Help

[tylerwitt34]

So my truck doesn't always go into 4wheel dirve when u turn the knob there and the hubs in auto, but when u put it there in lock it always works. I'm am concerned about the axle seals i mean i just replaced them this fall when me and a buddy did the ball joints but when u put the truck in 4wheel drive and the hubs are in auto when it doesn't work there seems 2 be a real loud whissing noise from the left side(Driverside) kinda like a big shuttering noise from the left side. So does anyone think its the damn axle seals they were replaced this fall. If not steer me in the direction were 2 start. Plan on taking it 2 the dealership for that recall and want them 2 look at it but if the axle seal that isn't cheap and i don't wanna drop another grand plus in this truck since i just add all my mods so please help and give me what u think it is.

[alabamafrog]

The system is real easy to test with a hand held vacuum pump/gauge. I got mine for about $20 at a parts store. All you gotta do is hook it to each hub and make sure you can pull about 15” of vacuum on both hubs to see if one or both are leaking. If the hubs are good then you can hook it to the vacuum line and flip the dash switch, one way you should read 6”, the other way you should read 15”, the vacuum pulse only lasts about 30 seconds after you flip the switch. I aint no Ford tech though.