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4x4 only works when locked in

3K views 17 replies 6 participants last post by  1999powerstrok 
#1 ·
I have a 99 7.3 I had a vacuum leak in the hubs so I took them off and replaced all the orings. That solved my vacuum leak but when I switch to 4x4 on the dash it does not lock in. It does work when I get out and lock them in manually. When I do lock them manually it is always in 4x4 even when the switch is on 2x4. If anyone has any idea on what this might be I would really appreciate it.
 
#2 ·
It could be a leak in the vacuum lines or possible still a problem with the hubs themselves. One thing is for sure, you still have a vacuum leak somewhere.
 
#5 ·
Your hubs need a rebuild, or you have a vacuum leak. You verified that you hold vacuum, so you need to rebuild your gear. I suggest Warn in lieu of a rebuild, but a rebuild is cheaper.
 
#6 ·
When you lock the hubs manually and flip to 2wd, your not in 4x4 unless you have a transfer case issue too. What you will see is that the front drive shaft turns but it will be in neutral at the transfer case so no power goes to it.

As for the auto hubs, like the other said it's either bad hubs or a leak.
 
#7 ·
When you have the hubs in auto shift into 4x4 and travel several feet in forward, then reverse several feet and then once more back into forward. Do all of this while the a/c is on max. If your a/c changes for the vents to the defrost... It's definitely a vacuum leak.
 
#9 ·
Sounds like your transfer case is stuck in 4x4... Is that what your saying?
 
#11 ·
When selecting 2wd, 4x4, and 4x4low does the transfer case ESPF motor make any sounds? You would hear it clicking... If its not check to if its getting power, if its not, check the relays. If they are good then its probably the 4x4 module. FYI, the soleniod can be jumped bypassing the 4x4 switch so you can rule out that too.
 
#12 ·
This post should help you out with jumping the relays... FYI this guy fixed his 4x4 problems, ended up being the 4x4 module

4x4 relay info
 
#17 ·
Look in your owner manual :thumb:... It's under you hood right next to the fuse box... There is two.
 
#15 ·
i bet your lines are dry rotted right at the hubs.
 
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