How does AUTO 4WD work/what does it do?

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ColdCase

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engineers selected this so the average driver can put it in 4wauto and get through 6" of snow without thinking about it.

The skeptics here will tell you RAM finance guys picked the 44 to save money and reduce warranty claims for those 50% mall cruisers that forget they are in lock mode when looking for a parking space.

By the way, for those needing a better system without sacrificing much ride, the 2500 powerwagon has all the goodies with softer springs than the regular 2500. This is the vehicle RAM probably intended to sell to those that need pretty good 4x4. The RAM auto is more for mall cruising but they failed to get the word out about the 1500 auto box. Some of us didn't want to go to the powerwagon, but expected splined lock at least in 4 low.
 

LouM

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This is incorrect.

A hypothetical thought experiment:

Let's assume that a situation as you describe is occurring.

The rear wheels are set on rollers and are free to spin. The front wheels are on dry pavement. 4 auto is selected.

As you press the throttle, the rear wheels begin to spin on the rollers.

The computer immediately detects the rear wheels spinning faster than the front wheels and sends current to the electromagnetic actuator, which applies a compressive force to the clutch basket.

At this point, the friction between the clutch plates causes the ballramp to force the clutch plates into compression and drive the front wheels.

The traction between the front wheels and the road surface retard are retarding movement of the front wheels, increasing the force exerted on the clutch plates by the ball ramp.

As you further mash the throttle, the engine produces more torque, and the ballramp forces the clutch plates together harder. All (100%) of the engines torque is transferred to the front wheels. The rear wheels will not rotate at a higher speed than the front wheels. When the front wheels begin turning, pulling the truck along, the rear wheels will be rotating on the rollers at the same speed.

This is fact. You don't have to take my word for it. Just disassemble your transfer case and you'll see how it works with your own eyes.


I'll draw a simple ballramp actuator and clutch in CAD and try to post it here. It'll help visualize how this system works.


I do not believe that you are correct, when I look into the operation of this t case the torque from the rear is what drives the ball ramps.
If you tried your test with the rollers and placed a block in front of the front tires you would find that all that powered the front axle is the elecricly activated clutch which can not handle much torque until the ball ramp increases the loading of the clutch. If you follow the power flow from engine to transmission to t case to the front axle.The clutch is after the ramps the clutch can not increase the capacity of the clutch pack the rear axle torque applied to the ramps is what clamps the clutch disc harder to increase the torque to the front, the electrical activation has minimal torque capacity.
 
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chrisbh17

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I really wish this thing wasnt such a mystery.

Someone mentioned they made some changes for MY2017 (or possibly 2016), I wonder if that causes different behavior than other years.

Even in 4-auto without rear wheel slippage, SOMETHING changes on my 2017 since my 2000RPM vibration feels stronger. Technically the only thing that should be different at that point is that the axle connector is engaged, but they must be sending some torque to the front even without slippage.

Not sure if its just torque from the electromagnetic clutch or if its actual torque driven from the xfer case. Also not sure if thats what "changed" for 2017 or not.

Hopefully going to get a good mount for our GoPro and will record what goes on in 4-Auto, but that still wouldn't give an idea of just how much power gets transferred.
 

Ken226

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The clutch pack is rated for 1600-1700 lb-ft of continuous throughput.

The Rams 5.7 Hemi has a peak torque output of 410 lb-ft.

So, assuming this highest load situation, your an a really steep hill pulling a really heavy trailer, and have about 10% rear wheel traction at, but still somehow 90%% front wheel traction.

Assume that your in 1st gear with an 8speed, at 4.7:1 ratio, and you also have the throttle floored, and are holding the engine RPM at the exact speed where peak torque is produced, and the front wheels have so much traction that they are pulling, with no slip whatsoever.

Then, in this situation, which is highly improbable but idealized and optomized just to stress the clutch as much as possible, the ball ramp is closing the clutch and the clutch has a throughout of (410x4.7x.9=1734lb-ft).

In the above situation the clutch is at the peak of it's rated through ouput, but not excessively so.

In the above scenario If the engines rpm changes the load is reduced. If the rear wheels gain more traction, the load is reduced. If the front wheels start spinning, the load is reduced.

The clutch packs throughput rating is calculated from it's friction material surface area, the materials coefficient of friction and the closure force from the ball ramp. The ball ramp closure force is calculated from the engines torque x the gear reduction ratio x the ball ramps mechanical advantage.


My degree is in Mech Engineering Technology, with a focus on Mechanical Design. More specifically, my last semester elective classes were on gear drives. I'm not guessing.

Yes, there are situations possible where the clutch pack could be overloaded, but those situations are highly improbable. It would require ALL of the following conditions:

100% front wheel traction, no wheelspin
0% rear wheel traction, freespin rear wheels
Engine RPM held at peak torque (TC off)
Lowest gear ratio (4 low)
And a peak load weight/roadsurface angle

So, you'd need to be pointed up a hill, attached to a load that prevents any forward movement, in 4 low, with 100% front wheel traction, with 0% rear wheel traction, no front wheelspin, and be at full throttle, and be holding the engine speed at it's peak torque rpm.

And, try to keep in mind, the rating is for continuous throughput. It limited to it's continuous throughput rating due to heat buildup. That rating is not the slip point, it's just the point where heat builds up faster than it dissipate s. It can take much more torque if not continuous.
 
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muddy12

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Even in 4-auto without rear wheel slippage, SOMETHING changes on my 2017 since my 2000RPM vibration feels stronger. Technically the only thing that should be different at that point is that the axle connector is engaged, but they must be sending some torque to the front even without slippage.

.

The axle disconnect being engaged will cause the front drive shaft to spin much faster than it does when it’s in 2wd.

With how far the front output of these cases sticks out with no support, it wouldn’t take much of an imbalance in the drive shaft, to cause a lot of vibrations.

And, even though the front shaft is not “supposed” to spin in 2wd, there is usually enough parasitic drag in the front dif, that it will still rotate(just at a slower rate).



Sent from my iPhone using Tapatalk
 

Ken226

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[QUOTE

And, even though the front shaft is not “supposed” to spin in 2wd, there is usually enough parasitic drag in the front dif, that it will still rotate(just at a slower rate).



Sent from my iPhone using Tapatalk[/QUOTE]

There is a lot of parasitic drag. Especially in the transfer case. The ballramp clutch is viscous, with a significant amount of fluidic shear between the plates. Even when in 2wd, the transfer case will cause the front driveshaft to spin because of this viscous shear
 

chrisbh17

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Kinda what I was thinking, I just need to prove it (dealer swears driveshafts and axles are fine). I was under the impression the front driveshaft would never move in 2WD, but if thats not the case its a good possibility it could be the issue.

I figure the GoPro video would be nice just to see when the driveshaft moves during normal operation and maybe to see if its vibrating too. And eventually trying to drive without the front driveshaft to see if the issue disappears in 2WD.
 

LouM

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The clutch pack is rated for 1600-1700 lb-ft of continuous throughput.

The Rams 5.7 Hemi has a peak torque output of 410 lb-ft.

So, assuming this highest load situation, your an a really steep hill pulling a really heavy trailer, and have about 10% rear wheel traction at, but still somehow 90%% front wheel traction.

Assume that your in 1st gear with an 8speed, at 4.7:1 ratio, and you also have the throttle floored, and are holding the engine RPM at the exact speed where peak torque is produced, and the front wheels have so much traction that they are pulling, with no slip whatsoever.

Then, in this situation, which is highly improbable but idealized and optomized just to stress the clutch as much as possible, the ball ramp is closing the clutch and the clutch has a throughout of (410x4.7x.9=1734lb-ft).

In the above situation the clutch is at the peak of it's rated through ouput, but not excessively so.

In the above scenario If the engines rpm changes the load is reduced. If the rear wheels gain more traction, the load is reduced. If the front wheels start spinning, the load is reduced.

The clutch packs throughput rating is calculated from it's friction material surface area, the materials coefficient of friction and the closure force from the ball ramp. The ball ramp closure force is calculated from the engines torque x the gear reduction ratio x the ball ramps mechanical advantage.


My degree is in Mech Engineering Technology, with a focus on Mechanical Design. More specifically, my last semester elective classes were on gear drives. I'm not guessing.

Yes, there are situations possible where the clutch pack could be overloaded, but those situations are highly improbable. It would require ALL of the following conditions:

100% front wheel traction, no wheelspin
0% rear wheel traction, freespin rear wheels
Engine RPM held at peak torque (TC off)
Lowest gear ratio (4 low)
And a peak load weight/roadsurface angle

So, you'd need to be pointed up a hill, attached to a load that prevents any forward movement, in 4 low, with 100% front wheel traction, with 0% rear wheel traction, no front wheelspin, and be at full throttle, and be holding the engine speed at it's peak torque rpm.

And, try to keep in mind, the rating is for continuous throughput. It limited to it's continuous throughput rating due to heat buildup. That rating is not the slip point, it's just the point where heat builds up faster than it dissipate s. It can take much more torque if not continuous.

The clutch pack at be rated for that much torque but it will not get that from the electrical engagement and with low traction at the rear it will not be engaged sufficiently to pass that torque thru, that is why it gets an over heat message when the clutch slips under low loading situations. Free spinning rears will result in that clutch slipping as it is not being forced into engagement.
 

Ken226

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It's not engaged electrically, the electromagnet only starts the reaction.

I have visually, with my own eyes, looked at the arrangement of parts inside the transfer case. I can see, exactly what those parts do, and how the interact with the other parts. It's obvious, when you physically look at the arrangement of parts.

When the electromagnet is energized, it pushes a multipiece ballramp on to a splined shaft. At that point, the rotation of the inner shaft rotates the rear half of the ballramp mechanism, which pushes the 2nd half of the mechanism forward and drives the clutch/steel friction plates into compression.

Let me repeat, electromagnetism is NOT forcing the clutch plates into compression.

The engines torque, forces a shaft to rotate. That shaft forces the rear half of the ball ramp to rotate. When the rear half of the ballramp rotates, balls roll up ramps, pushing other ramps on the 2nd half, which in turn, push the 2nd half of the ballramp against the clutch plates.

So, to put it simply. Power to the electromagnet just turns the clutch ON.

Think of the ballramp as being 2 plates mated together. If you grab each side of this 2 plate assembly and twist in opposite directions, the balls inside cause these plates too begin separating. It forces them apart.

When ON, the engine in forcing the rotation of one of these plates, forces the 2nd half to compress the clutch plates.

The harder the engine turns, the harder the 2nd plate pushes against the clutch plates.

This is s mechanical system, it is not an electrical system. Electricity only initiates the engagement. FORCE is what makes the front wheels start turning.

So, when the rear wheels try to turn, they apply a force to turn the rear wheels. This force is applied in 2 ways.

1st, Axial force, driving the clutch plates into compression.

2nd, when and only when, the plates are fully compressed, that force becomes torsional and makes the front wheels turn.

The amount of rear wheel/front wheel relative rotation needed to achieve full axial engagement is 60°

Unless, if your going forward then stop, and shift into reverse. If your going forward, then stop and shift into reverse, the wheels and hence the 2 half of the ball ramp will need 120° of relative rotation to achieve full axial compression from the ball ramp. This is because the balls must roll down the ramp, and back up the other side of the ramp, doubling the amount of relative rotation.
 
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Ken226

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Both half's of the ballramp look like this:

https://cobratransmission.com/bw441...3_2122&zenid=e0bef0093352e1344418273d463603dd

You can clearly see the helical ramps that the balls ride in.

Picture 2 of those, facing each other, with a ball trapped in each groove and an electromagnet pulling hem together.
One of those plates is connected to the rear drive shaft. The other on a splined shaft to the front wheels.

When the rear wheels slip, one of those plates will turn, forcing the other plate to compress the clutch plates. Then the clutch plates can compress no further, the whole assembly starts rotating, making the front wheels turn as well.


Under all circstances, unless your transfer case has been fried, the clutch plates grip each other much harder than your tires grip the road.

When you are only applying small amounts of throttle, the ballramp is only applying a small amount of force to the clutch plates. But due to the ballramps mechanical advantage, the clutch compression force still exceeds the force applied by the tires to the road.

This is because of the clock position differential between the 2 halves of the ball ramp. The design, by it's very nature means that any slipping in the clutch plates will serve to further compress the plates, and decrease the slipping.

Kinda self compressing. The more it slips, the harder it compresses untill it stops slipping. If the force is low enough to allow slip, the slip itself further compresses, intill slipping stops.


The ballramps mechanical advantage means that it's axial force output will always exceed it's torsional force output. It'll always be applying enough compression to overcome the tendency to slip. Low compressive force means even lower torsion force.

Unless, somethings toasted. Then, all bets are off.
 
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Ken226

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A quick evaluation:

The radius, from the center of the plate to the center of the ramp; 3 inches

Curvilinear distance the ball travels when it rolls from the center of the ramp to the edge; 2 inches

The rate of the ramps angle. The ball, in travelling is lifted by the ramp about 1/4 inch.

This gives it an 8:1 mechanical advantage.

The FL/lb torque advantage from the ramps position 3" from center is 4x

For every lb ft of torque applied to the ballramp, 24lbs of axial (clutch plate compressing) force is generated.

So, if your engine throttle position is applying 400 ft lbs to this ballramp, the clutch plates are under 9600 lbs of compressive force.

If your at full throttle, through gear reduction applying 1700 lb ft to the ballramp, there is 40,800 lbs of compressive force acting on the clutch plates.
 

LouM

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When you are only applying small amounts of throttle, the ballramp is only applying a small amount of force to the clutch plates. But due to the ballramps mechanical advantage, the clutch compression force still exceeds the force applied by the tires to the road.

This is the part of your idea of how this t case that is correct, the torque applied from the rear axle resistance is what applies the clutch after the electric starts the process. Simply put if the rear has no traction, ie wet ice, there will be minimal torque applied to the front axle.
This coupled with the programing makes for a t case that I detest and at times is a safety and health hazard.
IT IS NOT A LOCKED TRANSFER CASE.
You have agood day.
 

Ken226

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If pictures, calculations, logic and reason doesn't suffice, nothing likely will.

Borg Warner would clearly be well served if they stopped hiring all those sciencey engineer nerds and go with internet forum members instead. Boeing, Raytheon and Honeywell have no idea how much better their systems would work if they'd just stop trying to use math to solve everything.

I've posted explanation after explanation, calculations that anyone could verify, links to pictures and videos explaining, showing and definitively proving how this transfer case works.

If someone is so determined in their assumptions, or incapable of understanding, that they'll never let something as trivial as evidence get in the way, then I'd be foolish to continue putting any time or effort into it.

I don't recall ever trying to convince you that it meets your definition of "locked", you can define that term however you wish. I'm only explaining to those who are asking "how does 4 auto work", how it works.

If you believe me, that's good. If you don't believe me, that's equally good. I neither lose nor gain anything either way.

I wish you and your transfer case the best sir.
 
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skupko9680

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Okay all science aside (I like it thought) lets talk about how we use these trucks (me). One of the things I really liked was the 4 auto when I bought my truck. I missed the AWD system I had years ago in my *** rig and while I appreciate 4WD high when we have deep snow here in WI, that doesn't happen all that often. Instead we get a lot of mixed conditions. Its nice not worrying too much about binding but at the same time it is taking me awhile to figure things out. Some times its fun as I get a bit of slip and slide in 4 auto before everything engages and sometimes it scares me as in "****, am I going to slide out the back into a curb". Overall I like it a lot but would like it to be more predictable. Any thoughts?
 

chrisbh17

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Honestly this winter has been a bust for me...I really wanted to be able to mess with 4-Auto at least, but so far the LSD and 2WD has gotten me through everything without question.

Im only really concerned with deep-ish snow but we havent really had that here (we did, once, but I wasnt driving in it). Luckily the truck warranty is longer than 1 year :) so hopefully the end of this winter or next winter will give me something to test it out in.
 

Ken226

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My recommendations based on it's function and my experience:

Things to avoid.

1. Avoid getting into situations where you need to switch into 4wd while your sitting still 'Stopped', AND will need all 4 wheels to pull at the same time. Such as stopping halfway up an ice covered hill to shift into 4wd.

In this situation, the rear wheels will brake loose first, and likely spin half a turn or so before the front wheels engage. And the front wheels will engage quickly, probably spinning a little too.
Activate the 4wd at the bottom, and the application of power combided with the flexure modulus of the tires will have all 4 engaged and pulling before you even get to the hill.

2. Avoid areas where you'll need to go back and forth between forward and reverse without wheelslip. When you switch from forward to reverse you'll need double the wheelslip to engage the system. Then, when you switch back to forward, you'll need double the wheelslip again. Sucks if you need to rock back and forth.

3. Avoid sudden high speed engagement of the 4wd . This isn't likely to be a problem, unless you get your driving advice from the internet. The traction control will prevent damage, unless you've turned it off.

Example situation that could cause this: While stopped, you turn off traction control, engage 4 auto, then hit the gas. You'll immediately get high velocity wheelspin in the rear wheels, and the computer will power the ballramp mechanism, which will hammer the front wheels into engagement with a violent shock load.

If the traction control is ON, it will detect the high velocity wheelspin and reduce power before engaging the ballramp.

Things to do:

Turn on 4wd early. Once the rear wheels have turned a few times and the ball ramp has engaged, it'll stay engaged as long as your applying some power.

Don't be afraid to trust the stability control and traction control. Contrary to internet lore, it makes things better, not worse. The only time it's a net negative is when high speed eheelspin is needed to centrifugally spin mud out of the m/t tires lugs.

Don't try to outsmart the computer. It's programmed to start/stop actions based on sensory inputs. If your doing something the programmers couldn't forsee, the computer and traction control will behave in unpredictable ways.

Example: you put your truck on ice, and shift into 4 low to show everyone how bad your 44-44 sucks. You get out to film your rear wheels turning while the front wheels are stationary.

In this situation, the following occurs, cyclically, in fractions of a second. The rear wheels start to rotate, the ballramp electromagnet is energized, and the rear wheels start to rotate, depending on how slick the ice is under the front wheels, they may start to spin too, The stability control interprets this and wheelspin and begins selectively braking both the front the rear wheels (which causes the ballramp to begin clocking back and forth, and stop compressing the clutches, just making a nasty ass grinding noise), the wheels stop and the abs stops braking, then the wheels start rotating again, then the ballramp engages, then the abs kicks in again, then the ballramp releases, then the abs releases, then the wheels rotate, then the ballramp engages. The cycle repeats, multiple times per second, over and over, generating heat, wear and possibly damage. The exact timing, force and results of this cycle will depend on relative friction under each wheel, condition of the clutch friction plates, and the idle power transferred by your torque converter.

Don't: Test the 4wd by holding the brake and throttle at the same time. It creates a lot of stress on driveline systems, AND if you do happen to accomplish your goal of getting the rear wheels to spin, your ABS and stability control will interpret this as wheelspin and begin doing strange things, as well as reducing power. Also, while the ABS is modulating the pressure in the brake lines, the ballramp will be rapidly engaging and disengaging (picture the ballramp plate driving the front sitting motionless as the other plate is hammering back and forth), as the ABS is selectively modulating the right and left, front and rear brakes independently, reducing/adding power, and trying to figure out WTF is going on.




If you really want to test this system, here is how to do it:

leave the truck in 2wd, leave the traction control alone. back into some deep mud, snow or ice and get the rear wheels really dug in and stuck good. Stuck good enough that in 2wd, you cant get out but not so deep that the front wheels cant get you out. Leave the front wheels on some nice, dry, high traction surface. Or, put the rear wheels on a set of roller dollys, while leaving the front wheels on pavement.

Now, put it in 4 lock or 4 auto, and give it some gas. The instant the rear wheels slip, the traction control will slow things down to prevent it from engaging too violently, the ballramp will transfer all (100%) (the rear wheels will still be turning, but this doesn't count as torque since they aren't pushing against anything), of the engines torque to the front wheels and all questions and mysteries will be answered. The Hemi, and that 44-44 will yank your ass out of that mud so fast you won't believe what happened. All 410 ft lbs of torque will be applied to that contact patch of rubber between the front tires and the road surface.

When I started seeing all the internet complaints about the 44-44, this is the first test I did. I went over to Canyon Creek Road, just east of Glacier, WA near Mt Baker and stuck the back wheels in a couple feet of snow, with the front wheels on some pavement. I left my first -front wheel only- black mark. When all 4 wheels are spinning, the ECS will allow you to apply all the power you want.

Don't believe me? Before you respond and tell me how wrong I am, go find a muddy ditch.

I drive a 2012 Chevy Tahoe for 8 hours a day, 5 days a week, and my Ram Sport the other 2 days, in the Cascade mountains. The Tahoe has the 44-05, which is smaller but otherwise identical to our 44-44. It behaves the same way.

I get that Tahoe stuck plenty, since someone else owns it, i'm a lot braver in it. Above the snowline I have plenty of opportunities to stick the rear wheels in 2wd, then pull out with the front in 4 auto.

Where the 44-44 and the 44-05 both really work well is climbing really steep, loose packed rocky mountain roads. There are tons and tons of time when all 4 wheels are spinning at the same time, and the ballramp stays engaged, all 4 wheels keep powering on. The hardpack level switchbacks are easy, because you can make steep, 180+ degree turns without dragging or binding, and when you start climbing again, all 4 wheels are pulling again. In this application, the traction control works like anti-spin diff, when a wheel spins over a rock or spins out climbing loose gravel, the TC brakes it and moves power to the other wheel pretty seamlessly.
 
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barbosa

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For all the complaints i've read, the Auto 4WD has not failed me yet and I have intentionally gotten myself "stuck" with the truck in 2WD just to test it. I buried the back tires almost to the axles and then stopped, switched to 4Auto and it instantly crawled out of the hole every time. Granted I am in FL and there is never going to be a circumstance where I "need" 4WD to get around on public roadways.
 

Ken226

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Honestly this winter has been a bust for me...I really wanted to be able to mess with 4-Auto at least, but so far the LSD and 2WD has gotten me through everything without question.

Im only really concerned with deep-ish snow but we havent really had that here (we did, once, but I wasnt driving in it). Luckily the truck warranty is longer than 1 year :) so hopefully the end of this winter or next winter will give me something to test it out in.


We had an awesome storm a few weeks ago here in Northwestern WA. We had snow, frozen rain lots of wind and 6 huge power poles feel across the roads going into my employers building. The roads were blocked by downed poles, and for a week, we were driving through a muddy corn field to get to work. Guys that owned 4x4s were shuttling everyone else from a parking lot 1/2 mile away, over to our building. I got to dig some badass ruts through that field.

BTW, you can imagine what happens to a cornfield here, after an ice storm, where, as anyone who's ever been to this part of the country can attest, it rains here every single day for 3/4 of the year.

The first day of the storm had my truck encased in a 2" thick shell of hard, clear ice. I had to chip my way in. I installed a remote start the next week.
 

VA10

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Just like barbosa - I have purposely put my truck in awkward positions to test the 44-44. I have yet to get stuck or struggle. Last night I stopped my truck on back road that was all icy wet clay/loose gravel. I drove to the steepest point of the road which was about a 6% grade. Maybe steeper in in some spots.

results - I lightly applied throttle until the truck started to move for all transfer case modes.

2wd with lsd - both rear tires just kept spinning. I stayed on the gas for about 5 seconds. The truck never moved up the hill more than an foot. Traction never kicked it - thats how lightly I was applying throttle.

4auto - rears slipped for a about a full second until the fronts started to pull. it took another second for the fronts to get more power sent to them before the truck started to move up the hill. This got me up the hill as longs a increased the throttle.

4hi lock - instantly pulled my up the whole hill with out having to add any additional throttle. If you payed close attention you could feel the rear tires slip for a split second...I mean you could barely tell...performed just a like a part time t case. Honestly, If i have a 4x4 savy persons in the passenger seat at the time - I doubt they could have felt the transition.

4low - almost no throttle and instantly started to creep up the hill. acted like any other locking 4lo transfer case ive used.

all tests were performed from a complete stop.
 

Ken226

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And to be quite honest, you'd have got the same results if you had tested 4 auto and 4 lock in the opposite order.

4 lock first would have slipped a bit, then 4 auto would have engaged quick.

Likely, your first test rotated the ballramp into it's engaged position. It was still in that position when you switched to 4lock.

If u crawl under your truck and look at the transfer case, you'll see 1 single wire separate out of the main harness and enter the transfer case through a hole near the rear drive shaft.

The main harness plugs into a stepper motor, which operates a shift fork that shifts between low range and high range.

But that 1 wimpy little 14ga wire, rated for 12volts and a few amps, is all that operates the computers on/off controller of the 4wd modes.

That single wire powers the electromagnet that commands the ballramp on. Through that wire, Power on and the 4wd engages, power off and the next time u make a turn or stop, it takes the frontpart of the ball ramp rotates backwards a little, (relative to the back portion of the ball ramp), taking the pressure off the balls and a wimpy little wave-washer spring pushes the ballramps apart.
 
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