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

[Ken226]

Also, chrisbh17, keep in mind that there's significant fluid shear between the clutch plates.

Thd fluid shear will keep both halves of the clutch rotating, but not with enough force to actually transmit power.

 

[Ken226]

This week I had no option but to drive in deep snow parking lots had ten or so inches of snow, and every thing but the main street had deep snow due to how fast it was falling and the wind. Even in 4 lock when pulling out onto the road after waiting for a break in traffic the rear would spin then the front engage, it just seems violent, is there no way to get around that? Is that not causing damage? The deep snow was made worse by having to drive through.. over the snow berm in order to get onto the main road.

It's undesireable, for sure. I think allot of these cases may have been poorly shimmed from the factory. Does it behave the same in 4 auto?

I'm considering a complete rebuild on mine, just to see how much I can tighten things up. I own a machine shop, and if i do this rebuild, plan to manufacture my own shim to get the clearances down as small as possible.

I already have a set of spare clutch plates on hand I'll also swap in.

 

[MT Hillbilly]

It's undesireable, for sure. I think allot of these cases may have been poorly shimmed from the factory. Does it behave the same in 4 auto?

it is a bit worse in auto, but not much difference to tell you the truth.. my truck has about 100 g miles on it, so.. no doubt wear is playing a role. I don't like that it does this, but.. in actuality this type of situation is NOT the norm, so once or twice a year, will probably not blow it apart!
and as for traction control things start going south when its -13 and has been covered in snow and road slime for five or so hours... trip started out with rain. but while on main road 4 auto preformed exactly as one would hope.

 

[chrisbh17]

Also, chrisbh17, keep in mind that there's significant fluid shear between the clutch plates.

Thd fluid shear will keep both halves of the clutch rotating, but not with enough force to actually transmit power.

Interesting. So while the driveshaft is spinning it might not actually be turning anything in the diff? I dont think my GoPro can pick THAT up Got a vid of the front of the diff side of the front driveshaft...nothing looks out of the ordinary. It leads me to another question - can this truck be driven with the front driveshaft removed? Since the rear joint isnt a standard u-joint, if the whole thing is removed, will the output of the xfer case get messed up with no driveshaft installed?

Also, re clutch shims....there are a bunch of DIYs about rebuilding a similar Ford version of our xfer case. They make a special tool (that looks just like a handle of sorts) to weigh down the clutch pack then you put the "handle" up to the whole works to determine the gap that needs to be filled with a shim. Feeler gauge to determine the actual shim thickness then install the shim and you're done.

Does that "by hand" process really happen on every single xfer case clutch coming out of the factory? If so, I think its pretty easy to see how some can be worse than others. On top of the fact that there are a finite number of stock shim thicknesses....then is it a judgement call to go too thick or too thin?

 

[Ken226]

If I were shimming mine, I'd compress the clutch pack and shim for .005-.01 clearance. But, I have no idea what the current clearance is.

Driving without the front shaft in would probably be fine, if you could keep the fluid from leaking out the driveline yoke hole

 

[chrisbh17]

Thanks.

Got a video of the front of the driveshaft and didnt see anything out of the ordinary (doesnt seem to be wobbling, etc) so Im guessing its not a balance thing so I might not take the driveshaft off anyway.

So if its just a matter of the fluid spinning up the driveshaft in 2WD, could you somehow block the driveshaft, since there is no actual power going through it? Just seems weird to me that it spins at the same RPM in 2WD as it does in 4WD but without any power going through it. I figured it would kinda lazily spin up and down if there was really no power going through it.

 

[ColdCase]

Recall earlier in the thread that the shaft is also spinning because one front wheel is driving it through the diff (passenger side i think). You may get some annoying dif noise if you block the shaft.

 

[chrisbh17]

Recall earlier in the thread that the shaft is also spinning because one front wheel is driving it through the diff (passenger side i think). You may get some annoying dif noise if you block the shaft.

Ahh yes, I was thinking from xfer case to diff and not the other way around.

So, the front driveshaft will always be spinning at the same RPM in regardless of drive mode which means it could still be a source of vibration at all times. When it gets warmer I will try removing it and driving to see if anything changes. Just not sure how to plug the xfer case end so it doesnt puke all of its fluid (unless its already sealed inside somehow).

 

[Machria]

My comment was meant more about the fact that the more you spend the "cheaper" your transfer case seems to be. Not the fact that they make and sell "higher than base" trims. I 100% agree on buying what you want, exactly what I did (Big Horn). At the time I just assumed the t-case was somewhat normal, but it seems like it isn't. I havent had my truck that long so it may very well be a non-issue for me, at least until the clutches wear out.

The Big Horn trim and higher CANNOT get the tried and true 44-45 t-case from the factory, but Id be interested to see if someone ever swapped one in, instead of buying replacement clutches.

Understood. My point was simply they probably make/put on "cheaper" (or less 4x4 robust) Tcase's on higher end trucks because people like me that buy them, don't really need the better 4x4 tcase.

 

[ColdCase]

Ahh yes, I was thinking from xfer case to diff and not the other way around.

So, the front driveshaft will always be spinning at the same RPM in regardless of drive mode which means it could still be a source of vibration at all times. When it gets warmer I will try removing it and driving to see if anything changes. Just not sure how to plug the xfer case end so it doesnt puke all of its fluid (unless its already sealed inside somehow).

I think the shaft is spinning because of all the friction in both the Dif and T Case, so it ends up spinning as a steady state. With it blocked or removed you have different things spinning and perhaps a different steady state. You could always take the shaft to a machine shop to check its balance. I don't think there is any issue running without the shaft short of fluid leak, if you stay in 2WD. Shouldn't be a problem in other modes for a short period of time.

With the shaft blocked, the ring gear holds the pinion gear with the attached gage in a fixed position. The other half axle shaft is disconnected so it spins freely. The normally near stationary small gears spin up at probably 2x normal rate as the rotation has to go somewhere. That may give you different dynamics and noise, if it doesn't damage the diff. If you happen to accidentally shift to 4WD at speed, well that could be expensive.

With the shaft removed , the diff should migrate to a steady state where the friction is least.

 

[Dodgedaddie also]

My 2012 Laramie 1500 won't engage the 4wd ?, Turn the knob on dash and nothing happens? No clicking,,No Light on the dash?
It was working in the Morning, but that evening It would NOT activate.

Any Help Would Be A Help.​