This is what the shop manual has to say:marc_w said:I don't think our trucks have hubs... ? or at least lockable ones. ?
Aren't the wheels a direct drive to the front CV'd axles?
My understanding was Auto 4x just puts the truck in 'ready' mode. ?As it is, the front driveshaft already spins full-time... even in two wheel drive mode. ?With auto engaged, it's just letting the computer know to go ahead and throw the engaging switch in the front diff, when needed.
This acutator motor is on the front differential.The front axle control circuit consists of an electric motor which engages and disengages the front axle. The front axle actuator's motor consists of a Permanent Magnet (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.
The front axle actuator has four circuits connected to a front axle feed circuit, front acle ground circuit, front acle control circuit, and a front axle switch circuit.
Whenever a shift to AUTO 4WD, 4HI, or 4LO is requested, the automatic transfer case control module engages the front axle by grounding the front axle control circuit though a current limiting driver.
Yup, that's the one I was talking about. They used to be vacuum controlled on the older Chevy's. Finally they made it electric!ShapeShifter said:This is what the shop manual has to say:
This acutator motor is on the front differential.
Hmm.....So, to summarize, this is what happens in the various modes:
2HI: Front axle disconnected, transfer case provides no power to front, lock solenoid de-energized.
AUTO 4WD: Front axle connected, transfer case routes power to front, but energized lock solenoid prevents power transmission. When slippage detected, solenoid de-energizes, providing power to front.
4HI: Front axle connected, transfer case routes power to front, solenoid denergized allowing power to front.
4LO: Same as 4HI, but an extra stage of gearing is enabled in transfer case, providing lower speed but more torque to front and rear.
NEUTRAL: Front axle disconnected, transfer case shifted to disconnect front and rear properller shafts from transmission.
Sounds like we are talking pretty much the same thing, the difference being just a matter of degree.marc_w said:Yup, that's the one I was talking about. ?They used to be vacuum controlled on the older Chevy's. Finally they made it electric!
I thought it was located somewhere between the differentials (driveshaft) flange, and the pinion gear... Am I wrong there?
I think this is pretty much what I was assuming...
There is also an exploded diagram of the axle. From the looks of it, the clutch shaft is in line with the axle half shafts. It would appear to me that this clutch will disconnect the half shafts from the differential, preventing the spinning of the ring gears. However, it is not clear to me. It does not appear that the clutch is on the transfer case side of the diff.The Selectable Fopur Wheel Drive (S4WD) Front axle consists of the following components:
The front axle on Selectable Four Wheel Drive model vehicles uses a central disconnect feature in order to engage and disengage the front axle. When the driver engages the 4WD system, the Transfer Case Control Module sends a signal to the electric motor actuator to energize and extend the plunger inside. The extended plunger moves the clutch fork and clutch fork sleeve across the inner axle shaft and the clutch fork shaft locks the two shafts together. The locking of the two shafts allows the axle to operate in the same manner as a semi-floating rear axle. A propeller shaft connects the transfer case to the front axle. The differential carrier assembly uses a conventional ring and pinion gear set to transmit the driving force of the engine to the wheels. The open differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force. This prevents tire scuffing when going around corners and premature wear on internal axle parts. The ring and pinion set and the differential are contained within the carrier.
- Differential Carrier Housing
- Differential Assembly
- Output Shafts (Left and Right Side)
- Inner Axle Shaft Housing
- Inner Axle Shaft (Right Side)
- Clutch Fork
- Clutch Fork Sleeve
- Electric Motor Actuator
Yeah, Definitely!ShapeShifter said:Sounds like we are talking pretty much the same thing, the difference being just a matter of degree.
What movie was that there... Speed, with the guy under the bus?I have not crawled under my truck recently while I was switching it between different modes, so I can't tell you for sure what was spinning and what wasn't.
Yeah, that's definitely reasonable. I honestly haven't spent a whole lot of time in Auto.But I can tell you that when I switch into AUTO 4WD, I do notice a difference. I don't so much hear it, as I feel the extra gear drag/vibration at times. My assumption is that the difference is that there are more parts spinning in AUTO as opposed to 2HI.
WOW... This one surprised me. I didn't think the front diff operated like this. It's almost like a ARB air locker, with the locker on the outside of the diff. Yeah though, you are definitely correct here.Page 4-124
There is also an exploded diagram of the axle. From the looks of it, the clutch shaft is in line with the axle half shafts. It would appear to me that this clutch will disconnect the half shafts from the differential, preventing the spinning of the ring gears. However, it is not clear to me. It does not appear that the clutch is on the transfer case side of the diff.
Uhg... I haven't cracked the cases on a front diff (yet) (hope I never need to!), so this is beyond me... I tried piecing things together, but my brain works better holding pieces in my hand.Take a look at it marc_w, and let us know if it looks the same or different from your past experiences. Also, see if you can figure out what parts are connected/disconnected by that clutch. I'll leave it to people with more experience than me to determine what's really going on.
I agree completely... for both statements...I'm curious to know how it really works, but my guess is that we're really getting down to the nit-pick details here.
For general information, it's probably enough to say what was stated in the earlier posts, where AUTO 4WD is "half on" waiting for the transfer case to give it power. To call it "locking the hubs" puts it in terms that many people can understand, even if it's not entirely technically correct.
LOL!marc_w said:What movie was that there... Speed, with the guy under the bus?
ROFL!I use 4HI on ocassion to get going up tricky snow covered hills and what not, and boy is THAT noticeable! ?It grumbles and whines more than.......... me...
I had trouble interpreting just how it works myself, which is why I posted it. Now, if I could just hold it in my hand and spin the gears while sliding that clutch fork back and forth, I'd be able to see what's happening. But just looking at the diagram?Uhg... I haven't cracked the cases on a front diff (yet) (hope I never need to!), so this is beyond me... ?I tried piecing things together, but my brain works better holding pieces in my hand. ?
D'oh! I guess perhaps I'm a bit hard on my Av then. . The difference in "slipperyness" of the conditions doesn't seem as critical to me as the torque multiplication. I've yet to be in mud or sand where I wasn't better off in 4hi... but trying to get a 3 ton Av to crawl over boulders... 4lo does wonders! You don't have to give it as much gas, thereby avoiding potential damage as you come down off of rocks. The extra torque on hand erases the need for a "running start" at many boulders and hills. 4lo is safer and actually easier on your Av (although Chief's point remains about wear and tear on the drive train) if you do any hardcore 'wheeling.Chief said:4-Lo - first, if you HAVE to use 4-Lo, you're probably not where you should be. ?Good for using in extreme conditions - very deep snow, very soft sand, deep soupy mud, pulling or pushing up a steep/slippery ramp (like a boat ramp). ?Extended driving in 4-Lo should be avoided to extend the life of your vehicle. ?Although you can achieve highway speeds in 4-Lo you should generally stay below 30 MPH. ?Again if you're going faster than that you're probably going to fast for conditions or you don't need 4-Lo - only excpetion to his would be very deep sand or mud where momentum is key.