Jeep Transfer Case: NP231/NVG231
The NP231 has an aluminum case and it should have a tag on
the back saying New Process Gear, Model 231. New versions
of the NP231 are refered to as NVG231 or NV231 which stands
for New Venture Gear. The tag on the back of the transfer
case will reflect the name change. Only the name is different.
A NV231 HD model is used in some ZJs. Presumably this is a
"heavy duty" version for Jeeps with the big V8s.
There are versions of this chain driven
transfer case that take 21 and 23 spline input shafts. The 23
spline version is used behind the AX-15 and the 21 spline is
used behind the AX-5 and the BA 10/5. The output for the front
driveshaft is on the drivers side. Low range is 2.72 and high
If you own a 21 spline NP231 and you want to swap in a 23 spline
transmission, you can either look for a cheap 23 spline NP231 at
the junk yard or go to your local Jeep Parts Dealer and order up
a new input shaft part #5300-6085. This is the part you need to
convert your NP231 to 23 spline input.
Since 1988, the NP231 has been the "Command Trac" transfer case used
in Cherokees (XJ), Comanches (MJ), and Wranglers (YJ). It has been
the "Command Trac" transfer case in the Grand Cherokee (ZJ) since its
introduction. The new Wrangler (TJ) continues to use the NP231, but the
NP231 used in the TJ has a different tail housing that
allows the removal of the drive shaft with out losing transfer
Both version of the NP231 used in the Wranglers have an over all
length that is long for a short wheel base vehicle. This can cause
driveline vibration and premature u-joint failure especially
for a lifted vehicle. There are kits to convert the tail housing
to a standard yoke to allow the use of a longer rear drive shaft.
There is also a 4:1 low range reduction kit for the NP231.
Wrangler are only available with "Command Trac", so the NP231 or NP207
are the only transfer cases available from the factory in any Wrangler
Last modified Wednesday, 01-Dec-2010 09:13:58 MST
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