4WD Issues

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Mar 9, 2016 | 05:56 AM

Dave Dirsa

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Joined: Nov 2015

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From: Westford MA

4WD Issues

Hi Guys. I have a Job 2 08 F350 crew cab. I plow in the winter with it. I am having an issue where the only way I can engage 4WD high is with manually locking the hubs. When i turn the switch in the cab to 4WD high, the light on the dash will light up. But it will not engage untill I turn the hubs manually. 4WD low works normally. Hopefully someone will have some thoughts.

Mar 9, 2016 | 11:06 AM

bdiomus

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Joined: Jan 2016

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From: Keller, TX

maybe vacuum?

There are a number of vacuum lines you can check for leaks. With the hood up, can you hear the vacuum pump run at all when you switch it into 4Hi? If so, how long? Mine runs a minute or so while it rebuilds vacuum after I put it into 4wd.

Mar 9, 2016 | 11:15 AM

Dave Dirsa

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Joined: Nov 2015

Posts: 43

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From: Westford MA

Quote:

Originally Posted by bdiomus

Solid question. Not sure. Check with engine off?

Mar 9, 2016 | 12:07 PM

bdiomus

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From: Keller, TX

Either way...engine running is fine, but let it run a few min before testing to give the pump time to build up vacuum. You can get a better idea if there is a leak by using a vacuum pump with a gauge, that would yield more exact results. Turn the floor vents on high as well (temp doesn't matter)...if the leak is bad enough air will start start coming out the defrost when you hit turn flip the switch for 4wd.

Here are a few threads that should be helpful...

https://www.ford-trucks.com/forums/1...-engaging.html
https://www.ford-trucks.com/forums/1...to-engage.html
https://www.ford-trucks.com/forums/6...-clicking.html
https://www.ford-trucks.com/forums/6...cuum-pump.html
https://www.ford-trucks.com/forums/1...-solenoid.html