4x4 issue
Thread Starter
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Cross-Country
Joined: Feb 2015
Posts: 96
Likes: 3
From: Alabama
4x4 issue
I ran into a little trouble this past weekend, parked off the side of the road, heavy rain, went to leave, and was spinning rear wheels. No problem, just select 4 high and be on my way. Unfortunately 4 high did not seem to help any, still spinning rear wheels. Tried 4 low, same results. Pulled rear end locker switch and with a little side drift pulled out.
So why no 4H or 4L, all indications in the cab show good shift, and in selected 4x4, but no power to front wheels. I went out and manually locked in the hubs, and presto had power to front wheels. At this point I was thinking a vacuum issue. Reading online, I found that if you have a vacuum issue, and select 4H or 4L the cabin air should switch to defrost. I still retained full normal control of my cabin air settings, so I'm not thinking this is a vacuum issue. Maybe a signal issue?
Anyone have a suggestion as to where I should look next?
Thank in advance for any assistance.
So why no 4H or 4L, all indications in the cab show good shift, and in selected 4x4, but no power to front wheels. I went out and manually locked in the hubs, and presto had power to front wheels. At this point I was thinking a vacuum issue. Reading online, I found that if you have a vacuum issue, and select 4H or 4L the cabin air should switch to defrost. I still retained full normal control of my cabin air settings, so I'm not thinking this is a vacuum issue. Maybe a signal issue?
Anyone have a suggestion as to where I should look next?
Thank in advance for any assistance.
Cargo Master
Joined: Apr 2010
Posts: 2,405
Likes: 4
You are correct, the vacuum signal did not lock your hubs. You could have a vacuum issue or the hubs might need service. Start by sitting in the cab key on engine off, and switch your environmental controls from floor to defrost until the stored vacuum is consumed. You should be able to get your vacuum pump to cycle on and off.
Thread Starter
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Cross-Country
Joined: Feb 2015
Posts: 96
Likes: 3
From: Alabama
Moved environmental controls from floor to front, to defrost for about 10 min, with key on, but engine off. Never heard the vacuum pump come on, and air output moved accordingly. With engine off and key on, switched from 2H to 4H and 4L, I could hear the transfer case shifting. Switched back to 4x2 and cycled through the environmental positions again, still no pump sound that I could hear, but the air output still moved to selected position.
Hotshot
Joined: Nov 2013
Posts: 10,107
Likes: 96
From: Hempstead, TX
I'm not certain they are vacuum operated. I know several - if not all - are servo driven. I can assure you that the vacuum pump is engine driven though. Unless you are driving a 350 DRW and up, you also have vacuum brakes, so pumping the brakes will also use up the vacuum.
Cargo Master
Joined: Feb 2008
Posts: 2,862
Likes: 44
From: Tooele, UT
I believe you have to be able to roll forward for the automatic hubs to engage. I'm not sure but in my '15 I noticed that it doesn't engage until I roll forward a few feet. But like you said it should engage instantly when you manually lock your hubs.
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Thread Starter
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Cross-Country
Joined: Feb 2015
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From: Alabama
Rolling forward of backwards had no effect on engaging my hubs while in auto. Still chasing this issue.
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Thread Starter
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Cross-Country
Joined: Feb 2015
Posts: 96
Likes: 3
From: Alabama
according to the owners manual to enter 4H you just have to move the selector switch, hubs can be in auto or locked position. To shift into 4L the truck needs to be in neutral and moving at a speed below 3 mph. My transfer case performs as advertised in all situations (front drive shaft locked to transfer case) in 4H or 4L, but the front hubs (axles) will not lock while in the auto position, they do lock when manually put in the LOCKED position.
Logistics Pro
Joined: Mar 2005
Posts: 3,523
Likes: 2,479
From: West Michigan
I suspect your vacuum pump is ok, as it runs continuous when the engine is running. However, there has to be a valve that gets actuated to actually apply the vacuum to the front hubs. That valve could be what is faulty.
As for 4H or 4L, if everything is working properly, you can automatically switch to either in AUTO mode. Locking your hubs manually has no bearing on 4H/4L other than actually engaging the hubs to the front drive axle shafts.
As for 4H or 4L, if everything is working properly, you can automatically switch to either in AUTO mode. Locking your hubs manually has no bearing on 4H/4L other than actually engaging the hubs to the front drive axle shafts.
Logistics Pro
Joined: Mar 2005
Posts: 3,523
Likes: 2,479
From: West Michigan
You could try tracing the vacuum lines from each of the hubs to see where they intersect, and then go from there. Have you checked for any blown fuses? Those valves are electrically driven. In the owners manual for my 2016, looks like Fuse #39 - 10A 4x4 Hub Lock would be a good place to look....
Thread Starter
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Cross-Country
Joined: Feb 2015
Posts: 96
Likes: 3
From: Alabama
I agree, need to trace lines to valve, and expect to find relay close. I did check the fuses, #38 and #39 on my 2011.
I'm really surprised no one has replied with where the valve is, but time will tell, if nothing else, by the end of this weekend I will post the location.
I'm really surprised no one has replied with where the valve is, but time will tell, if nothing else, by the end of this weekend I will post the location.
Lead Driver
Joined: Nov 2005
Posts: 5,216
Likes: 4,219
From: Kaysville Utah
Lock in your front hubs and engage 4x. Try to spin tires and see if they are engaging. The vacuum engages the hubs and faulty vacuum will leave the front hubs open. But if they front axle works after Manually locking them in. It is a fault somewhere in the vacuum system.
If after manually locking the hubs and you still have no power to the front axle, The problem is elsewhere
If after manually locking the hubs and you still have no power to the front axle, The problem is elsewhere