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Question on my 2011 Duramax 2500 do the hubs lock when you put it in 4 x 4 low? It feels like they are locked but are they truly locked?
 

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Question on my 2011 Duramax 2500 do the hubs lock when you put it in 4 x 4 low? It feels like they are locked but are they truly locked?
UPDATE: I don't quite know what the hell I'm talking about; see posts further down.

I'm fairly certain that the hubs on these trucks are statically locked, all the time. I.e., the front driveline is always turning; by putting it in 4WD you're simply locking the front driveshaft to the transfer case input shaft (or, equivalently, the rear driveshaft).

If your hubs weren't locking when you put the transfer case in 4WD, you wouldn't actually be in 4WD because your wheels wouldn't be connected to the driveline. Note that on a truck with auto-locking hubs that aren't working/engaging/seating fully, you'll hear grinding from the front end when you make turns on pavement. That's the sound of the splines on the hubs scraping against the splines on the axleshafts.

Bottom line: put the truck in 4WD and make a tight (and slow!) turn on pavement. If you feel it hopping, it's in 4WD and everything is probably working just fine.
 

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No locking hubs as the front wheels are connected to the axle via splines, the transfer case disengages the front driveshaft and the axles disengage via actuator within the front axle housing.
 

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So the system has 2 actuators? I was under the impression it only has one in the tcase to engage the drive and another to shift the ranges. Wasn't aware of an actuator in the front diff.
 

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Yes they do.
 

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No locking hubs as the front wheels are connected to the axle via splines, the transfer case disengages the front driveshaft and the axles disengage via actuator within the front axle housing.
So the system has 2 actuators? I was under the impression it only has one in the tcase to engage the drive and another to shift the ranges. Wasn't aware of an actuator in the front diff.
Seems he's right (see item 46 below, "shift fork assembly"). Although I can't quite figure out how all this actuation business works...



 

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I'll be damned. Its nice to know I can still learn at my age.
I'm like jw though-- hard to figure why they designed it that way. After reading the ops info it seems that front tires will not hop when turned sharp it seems. Thanks MRay for the info
 

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I'll be damned. Its nice to know I can still learn at my age.
I'm like jw though-- hard to figure why they designed it that way. After reading the ops info it seems that front tires will not hop when turned sharp it seems. Thanks MRay for the info
They will hop/scrub on sharp turns on hard surfaces if in 4wd (high or low)
 

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I'll be damned. Its nice to know I can still learn at my age.
I'm like jw though-- hard to figure why they designed it that way. After reading the ops info it seems that front tires will not hop when turned sharp it seems. Thanks MRay for the info
They will hop/scrub on sharp turns on hard surfaces if in 4wd (high or low)

@redwngr is correct; I know this is true in my truck. This is pretty much unavoidable in any system that includes a mechanical lockup between the front and rear driveshafts; the only way to eliminate it is to use a differential, viscous coupling, or other coupling between the driveshafts that allows for a difference in speed.

Actually, now that I think of it, there's a way to eliminate it while keeping the driveshafts locked together: four wheel steering.
 

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Mine hops too but if I am reading the last paragraph correctly they can rotate at different speeds according to the description of the diff which they call "open". I always compared mine to a go-cart style. Guess I am lost with this.
 

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Mine hops too but if I am reading the last paragraph correctly they can rotate at different speeds according to the description of the diff which they call "open". I always compared mine to a go-cart style. Guess I am lost with this.
It's confusing, but what they're saying is that the front diff is open, this allowing the two front wheels to spin at different speeds. However, since the front and rear driveshafts are locked together, you'll still experience hopping since the average of the two front wheels' tracks is greater than that of the rear wheels during a turn. But you'd experience even more hopping if the front diff was locked, this forcing the front wheels to both turn at the same speed. The truck would be damn near undrivable on pavement like that.
 

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JD, that shines a light on it. I forgot that system deals with 2 driveshafts. Thanks, now I understand.
 
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