Project BAD Monkey 2001
Transfer case upgrades
The stock NP231D transfer case under my truck. This page covers removing and completely disassembling and
rebuilding my T-case. I got the rebuild parts and some upgrades like a fixed yoke rear output shaft and
6 pinion planetary gear from
JB-conversions
I first drained all the oil and unhooked the speedo gear wires.
I then removed the front C.V. yoke, disconnected the shift linkage, and unhooked the vacuum hose.
After a serious battle with some hard to reach nuts I was finally ready to remove the T-case from
under the truck. I used a couple wood blocks on top of my floor jack to lower the T-case down.
This seal has been giving me trouble so I am replacing it.
The new seal inplace.
Now on the bench, I started to disassemble the T-case by removing the slip yoke extension housing and the
speedometer sensor.
Removing the rear housing exposes the speedometer worm gear and oil pump.
I removed the 2 snap rings that hold the speedo gear inplace and removed it.
Using the two pry spots on each end of the case I split the two case halfs exposing the guts.
I then removed the output shafts and chain at the same time and set them aside.
Next I flipped the T-case over to remove the input gear and planetary.
First I removed the seal plate and cleaned the silicon from both halfs.
The rebuild kit I got from JB included these awesome twin lip seals as well as all new bearings.
Heres the new seal pressed in place.
I then removed the snap ring from the input bearing and tapped the whole assembly out the bottom.
This picture shows the input gear and planetary gear assembly. This planetary gear provides the 2.72:1
reduction for 4 low.
I removed the snap ring holding the old input bearing in place and removed it.
One more snap ring (internal) and the input gear comes out of the planetary.
I replaced the roller bearing inside the input gear.
Heres the new planetary I got from JB. It has 6 pinion gears instead of the stock 3 significantly
increasing the reductions strength.
Now I can start putting this thing back together. I placed a wear pad in the bottom of the planetary,
inserted the input gear with a wear pad and retention plate and then reinstalled the internal
snap ring that holds it all inplace.
I installed the new snap ring on the new input bearing and pressed it into the case.
One external snap ring holds the input gear and planetary assembly inplace.
I then siliconed the seal plate inplace being careful to align the oil hole in the case with the cutout
on the seal plate.
This is a picture of the planetary gear reduction inplace. Note the giant outer ring that is fixed
in the case.
I removed the old front output seal and bearing and replaced them with new ones from the rebuild kit.
I pressed in the new bearing and secured it with a internal snap ring.
These double lip seals are realy cool, top of the line stuff.
Now I can start the fixed yoke output shaft conversion. I removed the synchro hub and drive gear from the
old shaft by removing a snap ring.
The fixed yoke conversion kit from JB comes with roller bearings for the inside of the drive gear.
I used a brass plug and a hammer to install the two new bearings. The original setup just rides steel
on steel with no bearings.
Heres the fixed yoke shaft next to the slip yoke shaft. You can see the two metal races that used to
be the bearing surfaces.
The first step to put this shaft in was to install the synchro / drive gear assembly using a supplied
thrust washer and snap ring.
I then slipped the range gear and range shift fork into the planetary (inside) and then put the mode
shift fork onto the shift ring and slid the new output shaft inplace. I then intalled the chain and
front output shaft and mode spring (not shown).
This unit is the internal oil pump for the T-case. I replaced the shaft seal and O-ring before reinstalling.
Before reinstall- ing the rear cover I installed the oil pumps sump tube and filter and placed the case
magnet in its place.
With everything inplace I siliconed the case halfs and slipped them back together.
One snap ring and the new speedo worm gear on the shaft and I siliconed and slipped the new rear
housing inplace. I replaced the shaft seal supplied by JB with a larger ID version to accomodate
the giant U-joint yoke I got from my driveline guy.
The new U-joint yoke completes the install of the shaft structuraly. The output bearing in the rear
housing is sandwiched between a flange on the shaft and the U-joint holding the shaft firmly inplace.
This picture also shows the speedo gear sensor inplace.
Finally I could slap this pig back on my truck. I jacked it up using a floor jack and a couple of blocks
of wood. I set the T-case input gear on the output shaft of the tranny and the thing just slipped
inplace.
It seems that putting the 6 nuts that hold the T-case inplace back on is a lot easier task than taking
them off. The reinstall went smooth thanx to the complete rebuild / upgrade kits from
JB-conversions
These guys know Transfer cases!
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I first drained all the oil and unhooked the speedo gear wires.
I then removed the front C.V. yoke, disconnected the shift linkage, and unhooked the vacuum hose.
After a serious battle with some hard to reach nuts I was finally ready to remove the T-case from
under the truck. I used a couple wood blocks on top of my floor jack to lower the T-case down.
This seal has been giving me trouble so I am replacing it.
The new seal inplace.
Now on the bench, I started to disassemble the T-case by removing the slip yoke extension housing and the
speedometer sensor.
Removing the rear housing exposes the speedometer worm gear and oil pump.
I removed the 2 snap rings that hold the speedo gear inplace and removed it.
Using the two pry spots on each end of the case I split the two case halfs exposing the guts.
I then removed the output shafts and chain at the same time and set them aside.
Next I flipped the T-case over to remove the input gear and planetary.
First I removed the seal plate and cleaned the silicon from both halfs.
The rebuild kit I got from JB included these awesome twin lip seals as well as all new bearings.
Heres the new seal pressed in place.
I then removed the snap ring from the input bearing and tapped the whole assembly out the bottom.
This picture shows the input gear and planetary gear assembly. This planetary gear provides the 2.72:1
reduction for 4 low.
I removed the snap ring holding the old input bearing in place and removed it.
One more snap ring (internal) and the input gear comes out of the planetary.
I replaced the roller bearing inside the input gear.
Heres the new planetary I got from JB. It has 6 pinion gears instead of the stock 3 significantly
increasing the reductions strength.
Now I can start putting this thing back together. I placed a wear pad in the bottom of the planetary,
inserted the input gear with a wear pad and retention plate and then reinstalled the internal
snap ring that holds it all inplace.
I installed the new snap ring on the new input bearing and pressed it into the case.
One external snap ring holds the input gear and planetary assembly inplace.
I then siliconed the seal plate inplace being careful to align the oil hole in the case with the cutout
on the seal plate.
This is a picture of the planetary gear reduction inplace. Note the giant outer ring that is fixed
in the case.
I removed the old front output seal and bearing and replaced them with new ones from the rebuild kit.
I pressed in the new bearing and secured it with a internal snap ring.
These double lip seals are realy cool, top of the line stuff.
Now I can start the fixed yoke output shaft conversion. I removed the synchro hub and drive gear from the
old shaft by removing a snap ring.
The fixed yoke conversion kit from JB comes with roller bearings for the inside of the drive gear.
I used a brass plug and a hammer to install the two new bearings. The original setup just rides steel
on steel with no bearings.
Heres the fixed yoke shaft next to the slip yoke shaft. You can see the two metal races that used to
be the bearing surfaces.
The first step to put this shaft in was to install the synchro / drive gear assembly using a supplied
thrust washer and snap ring.
I then slipped the range gear and range shift fork into the planetary (inside) and then put the mode
shift fork onto the shift ring and slid the new output shaft inplace. I then intalled the chain and
front output shaft and mode spring (not shown).
This unit is the internal oil pump for the T-case. I replaced the shaft seal and O-ring before reinstalling.
Before reinstall- ing the rear cover I installed the oil pumps sump tube and filter and placed the case
magnet in its place.
With everything inplace I siliconed the case halfs and slipped them back together.
One snap ring and the new speedo worm gear on the shaft and I siliconed and slipped the new rear
housing inplace. I replaced the shaft seal supplied by JB with a larger ID version to accomodate
the giant U-joint yoke I got from my driveline guy.
The new U-joint yoke completes the install of the shaft structuraly. The output bearing in the rear
housing is sandwiched between a flange on the shaft and the U-joint holding the shaft firmly inplace.
This picture also shows the speedo gear sensor inplace.
Finally I could slap this pig back on my truck. I jacked it up using a floor jack and a couple of blocks
of wood. I set the T-case input gear on the output shaft of the tranny and the thing just slipped
inplace.
It seems that putting the 6 nuts that hold the T-case inplace back on is a lot easier task than taking
them off. The reinstall went smooth thanx to the complete rebuild / upgrade kits from
JB-conversions
These guys know Transfer cases!