Hopefully this will help others in the future. 
4x4 help
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Cross-Country
Joined: May 2014
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4x4 help
I am a big fan of the convenience the auto locking hub system provides. as such i recently replaced the vacuum seals on the front axle, as one was leaking. When completed, both front hubs held vacuum for about one beers worth of time. i also replaced the vacuum line going to the hubs as they were dry rotted. 4x4 engages every time without a question, however after some amount of time the hubs disengage by themselves. I am thinking I have a vacuum leak somewhere upstream of the work I did, and I don't know this system very good, and am curious if that is the only possibility, or are there other issues that could cause this condition. It's an 05 v10. Thanks in advance for any reply.
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Joined: Jul 2010
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From: Media PA
The electric vacuum switch could be leaking or otherwise failing. It is mounted to the passenger side inner fender under the hood just rearward of the battery, it has the vacuum lines and a single 3 wire plug going to it.
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Vacuum was never a good idea in my opinion. When mine are engaged the heater
climate controls dont work properly..... the heat set on defroster does not blow out the top
so it looks like vacuum issues somewheres....
climate controls dont work properly..... the heat set on defroster does not blow out the top
so it looks like vacuum issues somewheres....
Veteran/Sheepdog
Joined: Feb 2012
Posts: 6,047
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From: Western AR
It is an incredibly simple system, even if it does use vacuum. Very easy to troubleshoot, and only a couple of parts involved. You have the vacuum canister that can start leaking along the seam that goes around it (clam shell design), the solenoid on the fender, the rubber boots that hold the lines at their 7 junction points (reservoir, relay, 90* elbow by the reservoir, the hubs themselves, and the 2 fender well connections. The line that runs from that 90* elbow to the two fender connections is a "hard line" with a T in it that should never fail unless it gets crushed. It runs under the engine on the frame rail (paired up with the brake line).
Yes, vacuum leaks under the dash can affect your 4x4 by leaking the vacuum built up in the reservoir, but they are pretty rare unless you go digging around under there and knock something loose.
Yes, vacuum leaks under the dash can affect your 4x4 by leaking the vacuum built up in the reservoir, but they are pretty rare unless you go digging around under there and knock something loose.
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The solenoid only directs vacuum to the hubs for 45 seconds when engaging. After the 45 seconds, the solenoid bleeds the vacuum off and there is no more vacuum being used for the hubs. If you are saying that your climate controls don't work whenever the hubs are locked, then maybe your hub lock vacuum solenoid is leaking and your pump can't supply enough volume for the loss.
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The solenoid only directs vacuum to the hubs for 45 seconds when engaging. After the 45 seconds, the solenoid bleeds the vacuum off and there is no more vacuum being used for the hubs. If you are saying that your climate controls don't work whenever the hubs are locked, then maybe your hub lock vacuum solenoid is leaking and your pump can't supply enough volume for the loss.
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While 4x4 is selected, does your vacuum pump continue to run?. Now switch back to 2x4 and see if your pump stops running after a few minutes. If it does, then I would say to replace your solenoid.
Oops, I made the assumption you had a diesel. If yours is gas, you don't have a pump. This is the way you can tell with a gas truck. After the hubs are engaged in 4x4, pull the two vacuum lines off the solenoid. The 1 line coming from the vacuum canister will be bleeding vacuum. Plug that line with a screw or something (you can leave the other line open) and then see if your defrost is working correctly.
Oops, I made the assumption you had a diesel. If yours is gas, you don't have a pump. This is the way you can tell with a gas truck. After the hubs are engaged in 4x4, pull the two vacuum lines off the solenoid. The 1 line coming from the vacuum canister will be bleeding vacuum. Plug that line with a screw or something (you can leave the other line open) and then see if your defrost is working correctly.
Last edited by erikkloss; Feb 5, 2017 at 07:12 PM. Reason: added info
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Im going to replace it. Thanks.
Laughing Gas
Joined: Jul 2010
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From: Flat Rock, MI
Mine occasionally did the same thing until I replaced the solenoid. Now in 4wd, heater controls function normally and 4x4 works.
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Great then thats what the issue is. I ordered it today and should have it in a couple days.
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