But what about the front to rear. Is there a diff controlling this power transfer?
No, it will send power to the front and rear equally.

And what about the front diff? Does this have any control mechanism to prevent all the power going to the front wheel with least traction
No, it is an "open" differential.

 

Great infro^^^^the auto lets your truck roll in 2wd but automatically kicks in when 4x4 is needed when set to auto...

 

Isn't Auto 4x4 bad for your transfer case and front diff, especially at higher speeds? Since it basically slams into 4x4...

 

Isn't Auto 4x4 bad for your transfer case and front diff, especially at higher speeds? Since it basically slams into 4x4...

Good question. I'm interested in the answer to this.

How is Auto 4x4 firstly activated and then how is it engaged.

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From what I understand auto goes ahead and engaged the transfer case but the wheels don't 'pull' unless needed. This will keep from damaging things when 4x4 is needed in a hurry. If you set your truck to auto and listen close when driving it'll make a little more sense.

 

Wade is correct, here is some more information on the transfer case found in most of our trucks.

The Magna Powertrain (MP) model 3023/3024 RPO NQH transfer case is a 2 speed automatic, active transfer case (ATC). The MP 3023/3024 ATC provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and NEUTRAL. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-6.78 Y (0-5 lb ft) of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.

The MP 3023/3024 ATC transfer case features a 5 mode shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a turn of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp continues to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly.

During normal driving situations, the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode, the transfer case shift control module monitors rear wheel slip speed, based on the inputs from the wheel speed sensors and/or vehicle speed sensor. When the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case 2/4 wheel drive actuator assembly. This actuator rotates the transfer case control actuator shaft, applying a clutch. The clutch is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is ramped up to the front wheels until the front wheel speed sensor matches that of the rear wheel speed sensors and/or vehicle speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again.

The MP 3023/3024 ATC transfer case has the added feature of also providing the driver with 4 manual mode/range positions:

•4HI - 4 Wheel Drive high range
•2HI - 2 Wheel Drive high range
•4LO - 4 wheel drive low range, 2.68:1 or 2.72:1 gear ratio reduction depending on model year and product content. Refer to New Product Information.
•Neutral
The driver may choose to select any of these mode/range positions while driving the vehicle. However, the transfer case will not allow a shift into or out of 4LO unless the following criteria has been met:

•The ignition switch is in RUN.
•The automatic transmission is in NEUTRAL.
•The vehicle speed is below 5 km/h (3 mph).
This transfer case also has a NEUTRAL position. A shift to the NEUTRAL position allows the vehicle to be towed without rotating the transmission output shaft. In the NEUTRAL position, the rear propeller shaft rotates the transfer case rear output shaft, in turn rotating the oil pump, thus providing constant lubrication during towing. NEUTRAL position may be obtained only if the following criteria have been met:

•The ignition switch is in RUN.
•The automatic transmission is in NEUTRAL.
•The vehicle speed is below 5 km/h (3 mph).
•The transfer case is in 2HI mode.
Once these conditions have been met, turn the rotary switch clockwise past 4 low and hold for 10 seconds. When the system completes the shift to NEUTRAL, the red NEUTRAL lamp will illuminate.

 

Awesome info wildchevy. Much appreciated

So am I wrong in concluding the following:

2wd is best for driving on the road when traction is consistently good. Fuel consumption is best and component wear is least
Auto is best for where conditions are mixed. Snowy or very wet roads, gatch and gravel tracks
4wd hi should only be used where the surface is consistently low traction because binding between front and rear can occur on high friction surfaces.
4wd lo should only be used on the same surfaces as 4wd hi but when lower gearing is required eg very steep inclines, technical ground and pulling out a stuck vehicle.

My query is with auto is can any problems be caused by the possibilities of relatively high speeds being present when 4wd is activated. I'm thinking of an aqua planing scenario for instance. I'm thinking that because there is aa active wet clutch in the system it should be fine

Can the torque values be tuned with something like an intune?

Ian

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This needs to be stickied somewhere. This is excellent information and I've been wondering about Auto 4WD myself since coming from a Jeep.

 

So they basically compensate for the required torque, so as not to damage anything? Good to know. Previous owner said he used Auto 4x4 quite a bit in Alaska. I've only used it once here - when it snowed last winter. Redneck buddy of mine at work said Auto is bad cuz it slams it into 4x4. He drives an Avalanche, so I dunno. I did feel a couple "thumps" when it engaged during the drive, but she still works without problems. Thanks for the answers guys.

 

This needs to be stickied somewhere. This is excellent information and I've been wondering about Auto 4WD myself since coming from a Jeep.

Awesome info wildchevy. Much appreciated

So am I wrong in concluding the following:

2wd is best for driving on the road when traction is consistently good. Fuel consumption is best and component wear is least
Auto is best for where conditions are mixed. Snowy or very wet roads, gatch and gravel tracks
4wd hi should only be used where the surface is consistently low traction because binding between front and rear can occur on high friction surfaces.
4wd lo should only be used on the same surfaces as 4wd hi but when lower gearing is required eg very steep inclines, technical ground and pulling out a stuck vehicle.

My query is with auto is can any problems be caused by the possibilities of relatively high speeds being present when 4wd is activated. I'm thinking of an aqua planing scenario for instance. I'm thinking that because there is aa active wet clutch in the system it should be fine

Can the torque values be tuned with something like an intune?

Ian

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No problem guys, I can do this for any of the systems on our trucks.

As far as tuning it with a intune you would have to ask Lew if the intune has that capability, I don't know.

 

In my opinion auto is useless to me. Give me power to all four wheels and I'll handle the rest. However, I do feel a little better about my wife's 4runner having auto 4x4 being that she may be a little safer with it.

 

If the Admin wanted to he could add a section called How It Works where the members could request this type of information and a member with GM access could respond with the correct information, not stuff like my buddy said this or the guy at the shop said that. Just a idea to think about.

 

In my opinion auto is useless to me. Give me power to all four wheels and I'll handle the rest. However, I do feel a little better about my wife's 4runner having auto 4x4 being that she may be a little safer with it.

But is there a problem with the front and rear axles binding when on a high traction surface (tar) in 4wd Hi?

I can definitely feel something when turning off the sand onto the road (or vice a versa) especially as I'm often in a tight is turn at this point

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Yea I can see that. Here in middle Georgia i guess there is never a need for it.

 

I was always told that Auto is bad when in cold conditions. Is this true? like here in Iowa when it stays below freezing all winter with lots of snow.

 

I was always told that Auto is bad when in cold conditions. Is this true? like here in Iowa when it stays below freezing all winter with lots of snow.

Can't see that being any more of a problem than any other transmission component. Auto gear box for instance

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auto is built for cold conditions lol. and there is no risk of damage even if it engages at high speeds (though i think the computer doesnt engage it over like 45 or 65 mph... idr)

the way 4 auto works is... well first lets get the parts straight

the front differential is an open differential with a clutch in it.

the Transfer case is directly after the transmission and has two drive shafts coming out of it. ours are chain driven with two ranges (gear ratios) as well as another clutch.

the rear diff is open unless it is a g80 where it is a mechanical LOCKER. not limited slip. i could explain how it works but in short, when one wheel slips it loads two clutch packs and locks the axles to the carrier in the axle housing.

the way 4 auto works is:

1) when 4Auto is selected the truck engages the front differential clutch pack. this locks the front diff to the front driveshaft. this is why you get less mpg more rotating mass. (note: your front axles are always spinning)

2) when the truck senses a slip using the same sensors as ABS it slowly engages the clutch in the transfer case (slowly) there is no chance of binding because if it does the clutch slips, furthermore this allows some torque to go to the front wheels. it continues this until the clutch is fully engaged. at this point the front and rear drive shafts are locked together and turn at the same rate. the rear may or may not be locked. the front is always open.

3) when the truck stabilizes it disengages the clutch in the transfer case and you are back in 2wd.

it can switch from 2wd to 4wd very very quickly. you can also engage 4wd hi at any speed. there is no hard shift or anything since the Tcase is in gear already it is just engaging a clutch. just like a manual. it is just engaging the clutch.

having used this in the winter it is great for starting in an unplowed driveway or subdivision and pulling out on to a plowed dry street. it is also good for when you are on slippery ground and the truck starts to skid. the front wheels engage and straighten the truck out very well.

it is worth noting that the 4wd auto is not meant to be run at all times and can wear out. (it is said the thrust bearing in the front differential clutch will wear) think of the tcase as a manual transmission. when at a read light you are supposed to shift into neutral and take your foot off the clutch because of the same reason. to disengage the clutch in a manual you have to put pressure on a thrust bearing. and it will wear out. same thing with the tcase clutch but it is reverse. it is normally not engaged and engages by applying pressure to a thrust bearing.

also, the OP's understanding of when to use each mode is correct.

 

Thanks for that info, I was curious as to if this worked with an internal clutch like I had thought. Now knowing for sure this will help me figure out why my truck engages at 20mph plus (I use a4wd in the yard just so I don't accidentally tear up the yard and sometimes forget to switch back to 2wd before leaving the driveway)

 

wow ok all of this is GREAT info...... but mine seems to be not working right?? i know ill never put it into auto but i use 4hi alot when going through the yard just so i dont rip things up but there are a few times when i needed to get through the mud and muck with my boat on the back and i wanted 4lo and it didnt work??? i would turn the thing to 4lo and it would sit there and blink and then the light would show over 4hi and the switch would be on 4lo still???? im not sure if its me doin somthing wrong but i dont want to have to take it into the dealer if i dont have to.

 

wow ok all of this is GREAT info...... but mine seems to be not working right?? i know ill never put it into auto but i use 4hi alot when going through the yard just so i dont rip things up but there are a few times when i needed to get through the mud and muck with my boat on the back and i wanted 4lo and it didnt work??? i would turn the thing to 4lo and it would sit there and blink and then the light would show over 4hi and the switch would be on 4lo still???? im not sure if its me doin somthing wrong but i dont want to have to take it into the dealer if i dont have to.

I've seen this happen when the driver hasn't put the vehicle into neutral before shifting from 4hi to 4lo

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i always put it into neutral befor goin into 4hi or 4lo but like i said its a coin toss if it will go into 4lo. should i go to 4 hi first then drop it down to 4lo???

 

No need to put it in neutral to go into 4high. And as far as going into low, you should just put the truck in neutral and go to low from 2, 4hi or auto.