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Part-time or On-Demand transfer case?

26K views 38 replies 18 participants last post by  Thunderhorse 
#1 ·
Ok - so when I went shopping for my current RAM back in May, I was on a mission to buy a 4X4. I have no intentions of "off-roading" - beyond gravel/dirt roads, deer camp, and having the extra traction when the snow and ice of the winter show up.

That being said, this is the first time I have shopped for a 4X4 (only other one I have owned was a worn-out old Border Patrol Expedition with a dysfunctional transfer case).

Anyway - I bought a BigHorn Crew Cab - which comes with (only one offered) - the "Electronic Shift On-Demand" transfer case.

I noticed when comparing models, the Express had a different setup - with different options on the selector for the 4X4. I believe the literature calls that one "part-time", though it too can "shift on-the-fly", I believe.

Anyway - I've read some gripes elsewhere (since buying my truck) about the "on-demand" version - mostly calling it not a "real" transfer case... others calling it more "all wheel drive" instead of 4X4.

What is your real-world experience with this transfer case?
 
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#3 ·
Hi Batt4CHRIST,

The one in your truck allows for on demand (full time) 4 wheel drive. There have been many many discussions about the 4 High, 4 Low settings on yours and I really can't answer one way or the other as I don't have one. What I DO have is the "Part Time" transfer case with the 355 LSD. When I go to 4 Low it locks the back axle and the front drive wheel giving me three driving wheels and pull it will! Now before we get into one of those "It does not work like that" discussion I have tested and retested this and if you even think about turning on pavement you will loose some fillings because that baby will tell you straight up it doesn't like the back wheels turning at different speeds on high traction surfaces.
4 Auto has the distinct advantage of being able to act like an all wheel drive system regardless of traction conditions. A very nice feature.

preachp
 
#4 ·
When off-roading in the Rocky Mountains for a week this summer, I tested out both my "AWD" and "4HI" settings. Maybe, just maybe, when in AWD, there was a fraction of a second delay in the front tires engaging when I punched the throttle in the gravel...maybe. And maybe, just maybe it was a little easier to make a sharp turn in AWD than 4HI without all of that tire slipping noise. Essentially, it drove like in 2WD when in AWD but the rear tires didn't spin.

In the end, for most everything I was doing, I simply used AWD or 4LO. I went everywhere I wanted in AWD and only used LO for the gear ratio when climbing or descending steep grades.
 
#5 ·
Its not AWD, its full time 4wd. It is still a transfer case and not a differential, although the effect is somewhat similar.
 
#8 ·
On demand is more expensive. I have avoided buying them since a few of my friends have grenaded the on demand tcases. (GM). I have not heard of any serious malfunctions on the rams however I don't particularly like the options that accompany the on demand cases. SLT trucks are fancy enough for me. Lol
I have not had a salesman try to push me one way or the other for t cases.
 
#9 ·
I wasn't pressured either. I knew what trim I wanted and that I wanted 4x4, the on demand case comes in the Lone Star. I figured it would be nice to have in case I get stationed somewhere where it snows or the roads ice over, because when that happens the whole road doesn't necessarily ice over all at once and I can avoid damaging my t-case. However, part time vs full time 4wd was not a factor that played into my decision to get a Lone Star over an Express.
 
#10 ·
The awd set up in an enhancement and costs more. Both have 2wd, 4 low, and 4 hi (both are locked) but the awd system allows you to stay in 4wd auto mode even if you are on dry pavement. It will kick in if you need it. I have the part time system. I drive in 2wd mode all the time, when I start to slip, I manually hit the button to move to 4wd mode, either hi or low depending on what I need. Your system will do it automatically.
 
#11 ·
I had the on demand case on the 1500 I had. It worked well with stock size tires. When you do to bigger tires it is not very difficult to overcome the preload on the clutch pack in the transfer case and cause premature wear of the clutches.
 
#12 · (Edited)
I have the 4wd on demand, haven't really had a chance to use it yet, although I did put it in 4 auto on some wet roads and it was nice to just be able to hit the gas while trying to pull out in heavy traffic and not have the back tires spin, worked instantaneous.
 
#13 ·
Ok, if your selector dial says AWD, 4HI, 4LO this means this; first setting is the transcase will allow the front and rear axels to move at different speeds via a central clutch pack in the transcase so that when on pavement power will go to both axels (and all 4 wheels if you have limited slip diffs) and the pack prevents driveline binding due to the two axels spinning at different speeds. Mode two is true 4x4 meaning that the front and rear axels are LOCKED at the exact same power input, aka each axel gets exactly 50% engine power and will spin at different speeds but always will spin. Advantage of this is in AWD mode say you lose 100% of traction at the rear axel, the central clutch pack will then be like "well thats not right" and then send all power to the axel with least resistance....leading to you going nowhere. In 4HI (true 4x4) the transfer case does not care if the front or rear axels are hovering in the air or on ice and have NO traction at all, 50% of power WILL ALWAYS go to each one. In short this means that you have a chance (a very low one mind you, if you have limited slip diffs) in AWD to lose all traction on one axel and then lose the ability to go forward, 4HI you need to lose traction at both axels to be screwed (again if you have limited slip diffs you need to lose traction at ALL wheels to be screwed) The final mode 4LO engages a secondary internal drive gear in the transcase that for some trucks (mine) you need to put the car in neutral to engage that leads to a MASSIVE drive ratio increase to the tune of 2.61:1 or even more that gives and insane boost to your torque at the ground that is more than some diesel trucks in normal mode. This is used when you need to have the highest possible traction and force/power applied (e.g. mud, launching a huge boat, acending or decending a very steep hill, pulling stumps up, pulling other trucks in a contest and watching their drive shafts blow up....you get the idea) the drawback to this is the car can't move that fast (25-35 absolute max) because of the effect of the very high drive multiplyer. The final thing you need to know about the 4HI and 4LO systems is that if you use them on dry or slightly wet pavement because the axels are locked at the same rotation speed you can cause massive damage to your truck due to the axels not being able to rotate at different speeds like they need to on a road surface, if you try to drive on pavement in 4LO your truck will literally start jumping in the air from the amount of force that builds up and in both modes turns are almost impossible on dry pavement and again in 4LO it will jump. Needless to say don't use 4HI unless you need to and you know what you are doing and NEVER use 4LO on roads and only use it if you know for sure its needed, most of the time 4HI will suffice. O! btw AWD mode is nice for higher speeds on roads for handling's sake and 2WD is awesome for drifts and power turns/burnouts. Hope this helped
 
#14 ·
O and before I go mine is a 2WD, 4HI, 4LO, electronic shift on the fly that will go into 4HI at any speed under 55mph and my dad (being kinda car retarded) ran it at 80mph in 4HI for years (11) on the highway in winter and nothing died so don't be too worried about using 4HI for de-iced roads in winter, it won't hurt it unless the road is DRY
 
#15 ·
Again, nobody's truck says: AWD, 4HI, 4LOW, and 2WD; they say 4AUTO, 4LOCK, 4LOW and 2WD because its 4 wheel drive, not AWD. A full time transfer case is still a transfer case, not a differential.
 
#16 · (Edited)
No thats most certainly not true, many newer ones have an AWD mode that is infact labeled as 4WD is some cars (my 2012 toyota sequoia being one) that uses a clutch pack in the transcase that will let the system act like an AWD unless you manually tell it to lock into real 4HI mode, 4AUTO is AWD is what I'm saying. I used AWD to make it easier to understand because most people know how AWD works.
 
#22 ·
4AUTO is AWD is what I'm saying.
And what I'm saying is that that is wrong.

The difference between AWD and 4wd is not determined by whether or not the vehicle has a low range. It is determined by whether the vehicle uses a center differential or a transfer case.
 
#25 ·
Okay......well let me ask this, can you turn on pavement with 4Auto on? Cuz in the sequoia there IS a center diff and turning is possible. IDK if it is somehow setup in a different way on the rams but to my knowledge it shouldn't just be switching back and forth from 4hi to 2wd al over the place
 
#27 ·
The Rams with 4 Auto are not AWD. They have a transfer case similar to the other truck transfer cases. They have 4 Lo. The real difference in the Ram with 4 Auto is that the front output in the transfer case has a clutch pack in it. The clutch pack is compluter controlled by varying the clamping force on the disks to allow slipping so that the front axles and u-joints are not overloaded. The clutch pack is supposed to lock solid so that there is no slippage when the selector is in 4 Lock. Unfortunately, the clutch pack is not capable of doing this when larger tires are put on the truck. There are times when the clutches will allow slipping in moderate traction conditions which can get you stuck where a typical transfer case will get you through. I thing the On Demand is OK for someone that does not use the truck off road.
 
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