Locking differential & 4WD

Tedzz

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When I pull the 4wd switch towards me to activate the locking diff. under 20mph, It doesn't lock up. One wheel still spins and the other rear wheel does nothing. Also the Auto locking hubs won't engage. I have to keep the hubs locked in. Could there be a common issue causing both of these issues?
 

sootie

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not likely the two issues are related unless it is the switch itself.

Does the 4x4 light come on when you select it and does the locking axle symbol show up when you pull the knob out?
 

mikeeg02

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In my experience, after you enable the locker, I slowly pull ahead and try to turn a little, that way if its not lined up, it will get the chance to engage. If you are stuck, and engage the locker, and just floor it, it probably wont get the chance to engage. If you upset it, it will remain disengaged. (I think the dash will not make it look like its working anymore IIRC) If you are stuck and want to engage it, stop the wheels, engage the locker, and softly apply throttle, it should engage. If one wheel is free spinning, dont even use the throttle, you want it to engage as smooth as possible IMO.
 

WHY NOT

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Ive had my truck pull the vacuums hose off the front hub before not letting it go into 4wd check that before you order new parts, slide those back on and was good to go.
 

mikeeg02

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I know on the older trucks it also controlled the heat. When the pump failed our you had a vacuum leak, you would only get defrost. My newer truck is a gasser, so I am unsure.
 

6.0 Tech

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The vacuum pump also operates the brake booster. I would look real hard at the solenoid on the top back of tye degas. Ive seen a bunch unplugged from other people working on them. Also seen broken vacuum lines there.
 

6.0 Tech

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Early 11 were hydro boost, i believe chassis cabs are hydro boost. Late 11-16 are vacuum. Not sure on the 17s yet, havent had much to do to them except oil pressure recalls...
 

mikeeg02

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Damn. That makes me sad. The '17 350 chassis cab I ordered should be here in a month or two. I'll be curious to look. That's disappointing.
 
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