Transfer Case vs. Center Differential

[cchase]

The question is, why do most pickup trucks on the market use a transfer case that basically cannot be used on dry pavement instead of a torque vectoring center differential as used on most AWD SUV's on the market?

There has to be more than cost as an issue.

 

[Steve S]

Full time 4wd needs some kind of differential action between the front axle and rear axle. On full time 4x4 pickups there is a differential action in the transfer case.

 

[strongt]

I would think it would have to be that the old style transfer case can take the abuse of off-road use and ect. Alot better the the car based AWD SUV's of today which are not made for off-road use. Also the old style transfer cases have a low range, which the torque vectoring center differential do not have. Thats why in in trucks and Jeep's that are built better for going of the pavement you have the transfer case instead of a torque vectoring center differential.

 

[Shannow]

Old style transfer cases lock the front and rear driveshafts together.

Means that you will get at least on front and one back wheel with torque (more if there's lockers and LSD involved).

Also means that circulating power will destroy drivetrains on the road if the transfer case is used on pavement.

A free centre diff can have you single wheeling off road.

 

[Gary Allan]

Strength, costs, durability, reliability. It's cheaper to have a lever than it is for a Torsen or viscous coupler. It's not just a torque converter sitting at one of the output shafts (but that wouldn't be a bad thing).

They can do it other ways too. Many of your hard core off road spiders are merely a Honda FWD front end turned sideways having the CV joints power the live axles front and rear.

 

[cchase]

Originally Posted By: Shannow
A free centre diff can have you single wheeling off road.


Understood, I'm trying to figure out what advantages/disadvantages lie in a transfer case compared to a center differential that has the ability to move power to the front or rear as necessary (as is becoming more and more common on vehicles today).

 

[GMBoy]

Originally Posted By: cchase
The question is, why do most pickup trucks on the market use a transfer case that basically cannot be used on dry pavement instead of a torque vectoring center differential as used on most AWD SUV's on the market?

There has to be more than cost as an issue.


GM pickups and SUV's offer a choice of AWD or a part time transfer case with a full time AWD selection in addition to the regular 4H and 4L modes. It's called Autotrac and has been out for quite some time. I think the best setup I've ever had personally was in my 2000 Jeep Cherokee. I had the optional system that had manual modes for off road only as well as a fulltime 4wd option. Loved it.

 

[cchase]

Originally Posted By: GMBoy
Originally Posted By: cchase
The question is, why do most pickup trucks on the market use a transfer case that basically cannot be used on dry pavement instead of a torque vectoring center differential as used on most AWD SUV's on the market?

There has to be more than cost as an issue.


GM pickups and SUV's offer a choice of AWD or a part time transfer case with a full time AWD selection in addition to the regular 4H and 4L modes. It's called Autotrac and has been out for quite some time. I think the best setup I've ever had personally was in my 2000 Jeep Cherokee. I had the optional system that had manual modes for off road only as well as a fulltime 4wd option. Loved it.


I understand that the option has been available for quite some time, I'm just interested in a comparison between a regular transfer case and a center differential with the ability to move power to the area with most traction in terms of advantages and disadvantages

 

[hsd]

A manual transfer case gives the driver more choices for off road conditions. My 97 Jeep T-case (NP 242) can provide rear wheel drive only for highway, 4x4 with f/r differential, 4x4 with f/r locked, 4x4 low range and a neutral for towing. If the differentials have been upgraded with locking capability, these vehicles can go just about anywhere.
My stock 06 Jeep has a full time 4x4 transfer case and electronic differential action provided by the ABS system. I must say it is better for daily driving as you dont have to manually shift anything. It just goes in the snow or whatever.

 

[VNTS]

Yes the jeep transfer cases like NV242 with the 4 hi where tourque is split 50/50 and you can drive on dry pavement are much better because the odds of you loosing traction on both axles at the same time is nil versus these on demand units where all the tourque goes to one axle until it slips.

My pal owns a body shop and after every snow or ice storm his shop fills up with smashed up Subarus LOL As he says, from the wheel that slips to the wheel that grips and into the ditch and to my shop to fix or junkyard

 

[ekpolk]

Originally Posted By: VNTS
Yes the jeep transfer cases like NV242 with the 4 hi where tourque is split 50/50 and you can drive on dry pavement are much better because the odds of you loosing traction on both axles at the same time is nil versus these on demand units where all the tourque goes to one axle until it slips.

My pal owns a body shop and after every snow or ice storm his shop fills up with smashed up Subarus LOL As he says, from the wheel that slips to the wheel that grips and into the ditch and to my shop to fix or junkyard


OTOH, that problem is really more of an issue concerning the lunkhead behind the wheel vs the vehicle itself. If you fail to learn, observe, and apply the operating limits of your machine (ANY machine, really), you WILL have problems sooner or later. That applies to any car, plane, train, ship, or whatever. And, of course, none of these systems are capable of repealing the laws of physics.

 

[IndyIan]

The automatic subaru system does have some odd handling characteristics, ie you spin up the front tires while turning, then the back tires kick in with a lurch sometimes, and with enough throttle, now all 4 tires are spinning and sideways you go WRC style... Very fun if you ask me but a bit of a surprise for people who don't practice winter driving(or don't fool around in a parking lot...

)
My Moms old CRV had a similar system and it was much easier to get way way sideways than my Tracker in 4WD(it has a transfer case) As long as you stay on the gas you can easily counter steer and power out of it. But if you chop the throttle, it would be hard not to spin out...

 

[UNC017]

Originally Posted By: cchase
The question is, why do most pickup trucks on the market use a transfer case that basically cannot be used on dry pavement instead of a torque vectoring center differential as used on most AWD SUV's on the market?

There has to be more than cost as an issue.


That, plus most "torque vectoring" (aka limited slip) transfer cases are virtually useless offroad unless they also have a "part time" mode that rigidly locks the front and rear axles together. There are a number of transfer cases that have both modes (torque vectoring and locked, such as the NP 249 used in Jeep Grand Cherokees for years). There are also some that allow full-time on-pavement use with a planetary center differential and no limited slip (NP 242). But typically the strongest cases are the simple ones that either offer 2WD or locked (offroad) 4wd in either a low or high range, like the NP 231.

If you read through the Jeep forums, the NP 231 is the most desired for offroading. The NP249 is well enough respected in terms of strength and offroad capability because it has the locked mode, but the only downside is the high cost of replacing the limited slip section when it wears out. Most credible sources say that the NP242 is just as strong as the 231 and offers one more setting (full-time), but rumors persist that its "weaker." What is no rumor is that there is more aftermarket support for the 231, and that is a deciding factor for a lot of serious offroaders.