4x4 vacuum-hub question/problem - Ford Powerstroke Diesel Forum
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post #1 of 5 Old 01-08-2013, 12:10 PM Thread Starter
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4x4 vacuum-hub question/problem

This is the first 4x4 truck I have ever had with a manual hub, so I am not exactly clear on a couple things.

1) I was up in the SoCal mountains last week snowboarding and I engaged 4wd high. Light came on but no 4wd. I got out and switched the hubs and 4high and 4low worked. That told me I have a vacuum problem. The transfer case works fine because 4low engages right away without problem.

2) When I have the ventilation system on either on A/C or vent and I switch to 4HI it goes to defrost. Does that mean that I have vacuum at the pump but not at the front axle, or no vacuum at all?

3) I can hear the pump running when it is switched to 4HI. I looked underneath and can't find an obvious vacuum leak at the axles. Kinda confused as to what my next step is. I need to have 4wd working, but I don't really want to do the manual hub thing. I like to be able to shift on the fly.

4) Does it cause damage to drive for a period of time with the hubs locked but still in 2wd? I spend a lot of time in the mountains and sandy desert in the winter time, and the roads are often clear then snowy then clear again. I don't want to get out and switch them all the time. As for the desert sometimes the sand gets deep when I don't expect it and stopping to lock hubs is the kiss of death in sand. I can just lock them in early, but again, I don't want to screw with the manual hub thing.

02 F250 PSD 4x4 auto CCSB
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post #2 of 5 Old 01-09-2013, 11:04 AM
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Tagging this post...have some of the same issues with the defrost although my hubs shift properly.

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post #3 of 5 Old 02-26-2013, 10:15 PM
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it means you have a vac leak...the system cannot keep up with controlling the vents inside while holding pressure on the hubs. default with no vac is the defrost. so until you fix the leak you will only be able to have one of the other.

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post #4 of 5 Old 02-27-2013, 05:49 AM
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You could have blown the o-rings in the hub if you don't see any obvious defects. Diesel o-rings has cheap repair kits. I would replace the vacuum line while I was at it, if I were you, but that's just me.

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post #5 of 5 Old 02-27-2013, 11:00 AM
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These look pretty slick:


Might help, sure won't hurt.

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hubs , vacuum

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