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Vacuum / 4X4 Problem

redxlt

redxlt

11
0
Union, MO
My 2004 F250 Superduty Lariat has a vacuum problem. The automatic hubs do not lock in when I select 4WD. I can feel the drivetrain kick in, but the hubs don't. I couldn't turn them to do it manually, but I fixed that tonight. Now, I noticed that when I select 4WD, it works but my blower/vents changes directing the flow out the defroster vents. I'm sure this is a vacuum problem, but where do I look. I checked the lines from the frame to the back side of the spindles and all looks good. Any help out there?

Mark
 
73F100Shortbed

73F100Shortbed

That's how we roll!
5,937
320
NJ
There is a vacuum pump that shows up as a common issue under some of the stuff I searched. But someone will have to come by and tell you where it is located exactly and how to test it. I'm not too sure. Another test is to put a vacuum pump on the spindle to see if it holds vacuum. But I'm pretty sure I remember hearing about another common issue because it affects your heat.
 
Last edited:
redxlt

redxlt

11
0
Union, MO
A guy I work with seems to think there is some kind of valve, or module on the firewall that could be the problem. Does anyone have any diagrams of where the vacuum lines run? And the routing it goes through? I have also heard of a method of very low pressure induced smoke into the line and looking for leaks. Has anyone ever tried this?

Redxlt
 

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