transfer case discussion on the FSJ lists - November 2002

Subject: Re: 241 vs 242 - Tcase 101 (long)

Remember, you ask for this.
  Decoding NP/NVG transfer cases is fairly simply, once you know the current
system.  Each tcase has a 3 number call out, like 231, 241, 242, etc.  These
three numbers will tell you the basics.

  First Number:  The number of speeds.  If it is a standard high range,
neutral, low range transfer case, the number is 2.  If it is a single speed
with no low range, like a 133, it gets a 1.

  Second Number:  The size of the case, physically, and has a lot to do with
how strong the case is.  The case sizes current are: 2, 3, 4, 6, 7.  With
22X series being the smallest and 27X series being the largest.

  Third Number:  This is where it gets confusing.  The third number tells
you what type of 4wd system is in the transfer case.  Current systems are
designated by: 1, 2, 3, 4, 6, 7 and I'll explain.

1 - Part time (PT) transfer case, manually shifted.  When in 4wd, front and
rear driveshafts are locked together.  If its a 2 speed tcase, then it would
have 4 positions, 2wd, 4wd, N, 4 loPT.  These cases are shifted by a lever
on the floor.  Example:  231, 241, 261, 271

2- Part time transfer case plus Full time (FT), manually shifted.  A geared
differential is used to allow the driveshafts to turn at different speeds,
while still applying torque.  Some are 4 position and some are 5.  4
position have 4FT, 4PT, N, 4loPT.  5 position boxes get a true 2wd where the
differential is bypassed and all the torque goes to the rear driveshaft.
These cases are shifted by a lever on the floor.  Example: 242, 242HD,
242AMG

3 - Part time (PT) transfer case, electrically shifted.  Everything is the
same as a -1-, except an electric motor is used to shift the transfer case.
Instead of a lever on the floor, you have a button or a dial on the dash.
Example: 133, 233, 243, 263, 273

4 - Part time transfer case plus Full time (FT), electrically shifted.
Everything is the same as a -2-, except an electric motor is used to shift
the transfer case.  Instead of a lever on the floor, you have a button or a
dial on the dash.  Example - 244

5 - Currently, there is no 5.

6 - Active on demand System.  Front and rear axles are constantly monitored
electronically to detect any differences in speed due to wheel slippage.
When a speed difference is detected, a computer signals the transfer case
clutch pack to engage. Torque transfer is transparent to the driver, meaning
the driver can tell it happened, like all four wheels are now pulling, but
you didn't have to pull a lever or turn a dial to activate it.  Example:
226, 236, 246

7 - Progressive on demand system.  The vehicle operates in 2WD. When
traction is lost by one of the driving wheels, power is automatically
transferred to the other axle. Torque transfer is transparent to the driver,
meaning the driver can tell it happened, like all four wheels are now
pulling, but you didn't have to pull a lever or turn a dial to activate it.
Example:  247

This is already way to long.  If anyone wants a break down of what case goes
into what, I could do it in another email.  NVG has a pretty informative web
site, complete with torque capacities at http://www.nvg.com/tcases.html.
The rest of the site is good as well.  If you go to the aftermarket sales
page and email or call in with a question regarding tcases, take a wild
guess who it gets referred too.  Have a nice weekend.


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FOLLOW ON DISCUSSION - 21 Sept 2007:

That page had a link to nvg's matrix, which sez for a 231:

max torque:
1885 (2556 Nm for you metric guys)

approximate GVW:
5920

So I guess as long as you didn't load the GW to gross, it would probably
be fine ;)

For what it's worth, the case in my cummins powered ram (271 or 273 can't
remember, but either way it's the same limits)
max torque:
7890

approximate GVW:
11500

The NV241HD that made it into some rams as well has a GVW or 11000 and a max
torque of 5555.