4x4 won't stay engaged while driving
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Registered User
Joined: Dec 2012
Posts: 7
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From: New York
4x4 won't stay engaged while driving
Ok so I've scoured the internet and all sorts of forums for the solution to this but haven't come up with anything yet.
While driving down the road in snowy situations my 4wd light will begin to flicker and eventually go out around 30 mph and above. If I let off on the gas my light will come right back on but if i keep on the gas the light turns off completely and you hear a clunk, but as soon as I let off the gas my light comes back on and 4wd works no problem.
At first I thought it was just a problem with the sensor that determines if i'm actually in 4wd or not so I replaced that. Didn't help. I then replaced the axle shift motor, didn't help. I then replaced all the vacuum lines coming from the axle shift motor to the transfer case. When I did this I found water in the lines and in the axle shift motor (don't know where or how i'm getting water in the lines). I put a heat gun to everything and flushed the lines and shift motor completely dry. Put everything back together and still the same result! I also replaced the switch in the transfer case because that was a little gummed up.
At this point i'm out of ideas and really don't know where to turn. I'm leaning toward a problem in a vacuum line or vent either under the truck or in the engine compartment.
any help anyone can offer me will be greatly appreciated!
While driving down the road in snowy situations my 4wd light will begin to flicker and eventually go out around 30 mph and above. If I let off on the gas my light will come right back on but if i keep on the gas the light turns off completely and you hear a clunk, but as soon as I let off the gas my light comes back on and 4wd works no problem.
At first I thought it was just a problem with the sensor that determines if i'm actually in 4wd or not so I replaced that. Didn't help. I then replaced the axle shift motor, didn't help. I then replaced all the vacuum lines coming from the axle shift motor to the transfer case. When I did this I found water in the lines and in the axle shift motor (don't know where or how i'm getting water in the lines). I put a heat gun to everything and flushed the lines and shift motor completely dry. Put everything back together and still the same result! I also replaced the switch in the transfer case because that was a little gummed up.
At this point i'm out of ideas and really don't know where to turn. I'm leaning toward a problem in a vacuum line or vent either under the truck or in the engine compartment.
any help anyone can offer me will be greatly appreciated!
Thread Starter
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Registered User
Joined: Dec 2012
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From: New York
I'll check them next! Am I supposed to have a cap on the vent that comes up by the passenger side wheel well? because I just have an open ended vent hose. Maybe thats where im getting water from?
Administrator
Joined: Apr 2010
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From: Clayton MI
Yeah, there is a little cap style do-hickey that goes on the end of that, but, it is NOT a plug. Needs to be able to breathe. 
LMC Truck, or, the dealer should have them. Might even find them at the local parts store..... 4x4 or truck shop should certainly have them.
LMC Truck, or, the dealer should have them. Might even find them at the local parts store..... 4x4 or truck shop should certainly have them.
Thread Starter
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Registered User
Joined: Dec 2012
Posts: 7
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From: New York
I took apart all the check valves yesterday and found one that was broken. I'm replacing that today along with the breathable plug in the end of that vent hose. Hopefully that gets me somewhere! Thanks for all your help HeyYou and I'll be sure to post back and let everyone know if this resolved the issue!
