4wd not working

[BlueOvalBoy29]

I've read threw some other threads and this is how far I have gotten. When I switch the nob on my dash to 4hi and 4low I can hear the transfer case engage and the light on the dash comes on. When I go under te truck the shift moves in slightly. I can manually force it the rest of the way and then 4wd works so its not the fork. So Im thinking its either a leak and it can't pull enough vacuum to pull it in all the way or the Diaphragm is ripped. I have a vacuum pump I just need to know which line to unplug and pull vacuum on to see if I can engage the front diff or not. Any other suggestions would be appreciated

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Also this is on a 99 5.4

[badazzfseries]

If youre standing at the front its on the top of the fire wall to the left (passenger side) there are to vacum switches it should be the one to the left if I remember correctly I'm pretty sure if the diaphram has any rips in it it wouldn't move at all but you could just unplug the lines from the diaphram and put the vac on it there you could put it on the lines and check the line then plug it in the diaphram to check it out

[BlueOvalBoy29]

Ok here's what I've got, I replaced the actuator 4wd worked, the next weekend I went out and it didn't. Pulled it up on a hoist and disconnected the actuator and tested all the lines as well as the actuator and everything checked out so I put it on a hoist and manually put it in 4 and all tires spun but when I got it back in the street it doesn't feel like its in 4 when I turn. I will be going out sometime this weekend to try it out but if it's not working what else could it be?

[Jersey_Joe]

Ok here's what I've got, I replaced the actuator 4wd worked, the next weekend I went out and it didn't. Pulled it up on a hoist and disconnected the actuator and tested all the lines as well as the actuator and everything checked out so I put it on a hoist and manually put it in 4 and all tires spun but when I got it back in the street it doesn't feel like its in 4 when I turn. I will be going out sometime this weekend to try it out but if it's not working what else could it be?

Did u try it in low? Just sayin cause mine in 4x4 high? I never feel it. But it is. I've seen it. But it just doesn't feel like it. Now. In low? It has the almost back pull feel in the steering that I'm thinking your talking about because that's why it doesn't feel like its in? See it in low and see if it does that so u know. And. No leaks? A vaccume leek sounds like its lurking. I know u said u checked it. But check it cold. And then again hot. May b your deal breaker. I had a similar prob and that's what I did. I found the leak cold. Just not hot. Good luck guys. Hope I helped

[joshpickworth]

I may be wrong but doesn't the electronic know actuate the hubs not the transfer case, at least that a what I thought bout mine

[BlueOvalBoy29]

I have not tried 4x4 low on the street just 4 high so that may be why I can't feel it in the wheel on tight turns but when I was in the dirt I did try 4high as well as 4lo and neither worked but up in the air on the hoist it did. I was thinking it could be an issue with the shift fork and actuator where they mate? Possible

[Jersey_Joe]

I have not tried 4x4 low on the street just 4 high so that may be why I can't feel it in the wheel on tight turns but when I was in the dirt I did try 4high as well as 4lo and neither worked but up in the air on the hoist it did. I was thinking it could be an issue with the shift fork and actuator where they mate? Possible

It may very well be. Mine broke lol. That's my next thing to talk about. All in all it was an easy fix but that's what happined to me

[BlueOvalBoy29]

Ok 4wd still is not working went out and tested today. What is the proper way to check the vacuum lines? I have a vacuum gage, and how much vacuum should it pull when trying to engage 4wd?

[Papa_J]

Actually, it should have vacuum when the 4wd is off. When you engage 4wd, the vacuum releases allowing the IWEs to engage. Then, the transfer case motor engages the half shafts. If the 4wd actuator goes bad (and most factory ones do), it likely got water in it from rain, which then made its way down to the IWE, which in turn could cause the IWE to fail. If the actuator and IWEs are fine,and it is holding vacuum, the next check is the transfer case motor. These often "stick", and can usually be persuaded to function with a few well-placed whacks of a hammer on the motor while it is trying to engage. Why this critical motor is so exposed to the elements and not in a more waterproof location is a question that has been asked over and over.

2005 Ford F150 Lariat SCREW 4x4 5.4L