Back in March I snapped the main shaft of my NP231 bouncing back off of a ledge. I swapped a case in from the local pick n pull and decided to build the broken one up with a SYE and wide chain. In the process of researching I found that the low range planetary gear could also be upgraded. I also realized that there was quite a bit of talk on the forums about the wide chain and also the planetary, but only found a couple good how to write ups, but they got a little scattered at times. Here is the write up by RockRodHooligan over on JeepForum: NP231 Upgrades that I got most of my information from. What I have tried to do is pull all of this information along with a few other sources together and condense it into one easy to follow start to finish build.
If you are attempting these modifications I am going to assume that you know how to disassemble the case in the first place. If not you pretty much just reverse this build.
Planned upgrades:
6 pinion low range planetary
Wide chain
JB Conversions Standard SYE
Here are a few comparisons of the upgrades and how to get them:
Planetary gears everything is exactly the same except for one having twice the number of gears. It is supposed to give twice the torque capacity of the stock gear. You can buy the 6 pinion planetary from JB Conversions for $250 or go down to your local pick n pull and strip down an NP241. I guarantee they will not know what it is and will ask you. I told them exactly what it was and they rang me up and charged me about $40 for a "rear end ring gear". :shaking:
There is a break in the years you need to be aware of. New Process changed the gear cut they used in '95. The old cut up to '94 had a rounded edge and '95 and newer have a sharp edge. RockRodHooligan has a couple great pictures of this on page 3 about a third of the way down in post #36. Midwest Transmission Center has a helpful chart about halfway down their page with applications that used the 241. I pulled my gear from a '99 Suburban 1500.
***Contrary to what many have said the 231d hd and 231c cases do not have the 6 pinion planetary. I have personally seen 2 231d hd cases and both had 3 pinions. I have seen one Chevy and it actually had a 4 pinion planetary which I guess would be an upgrade over stock, but if you are tearing a case apart just find a 241.***
You can see the size difference in the chain and the sprockets. The extra 1/4" is said to give about 30% more strength to the chain. I pulled this chain from a Dodge Durango with an NP231dhd case. Any dodge with the hd case should have it as well as a Chevy with a 231c case.
Comparison of the JB Conversion main shaft and the stock main shaft. The strength gains are pretty obvious in the tail shaft section. I shouldn't have to worry about shearing this one.
On to the build!
First install the input shaft in the planetary gear. There are two plastic thrust bushing type things, a retainer cap, and internal lock ring contained in the planetary. the wings on the thrust bushings and retainer will keep them aligned in the planetary shell. Place a thrust bushing in the bottom of the planetary then the input shaft. You may need to rotate the input as you slide it in to get the pinions to all line up. Then add the second thrust bushing retainer and lock ring.
[
]
Should look something like this when you are done.
The input/planetary assembly will slide in from inside out. The planetary will ride in the gear cut in the ring around the inside of the case.
Don't forget the lock ring to hold the input in place.
If you are attempting these modifications I am going to assume that you know how to disassemble the case in the first place. If not you pretty much just reverse this build.
Planned upgrades:
6 pinion low range planetary
Wide chain
JB Conversions Standard SYE
Here are a few comparisons of the upgrades and how to get them:
Planetary gears everything is exactly the same except for one having twice the number of gears. It is supposed to give twice the torque capacity of the stock gear. You can buy the 6 pinion planetary from JB Conversions for $250 or go down to your local pick n pull and strip down an NP241. I guarantee they will not know what it is and will ask you. I told them exactly what it was and they rang me up and charged me about $40 for a "rear end ring gear". :shaking:
There is a break in the years you need to be aware of. New Process changed the gear cut they used in '95. The old cut up to '94 had a rounded edge and '95 and newer have a sharp edge. RockRodHooligan has a couple great pictures of this on page 3 about a third of the way down in post #36. Midwest Transmission Center has a helpful chart about halfway down their page with applications that used the 241. I pulled my gear from a '99 Suburban 1500.
***Contrary to what many have said the 231d hd and 231c cases do not have the 6 pinion planetary. I have personally seen 2 231d hd cases and both had 3 pinions. I have seen one Chevy and it actually had a 4 pinion planetary which I guess would be an upgrade over stock, but if you are tearing a case apart just find a 241.***
You can see the size difference in the chain and the sprockets. The extra 1/4" is said to give about 30% more strength to the chain. I pulled this chain from a Dodge Durango with an NP231dhd case. Any dodge with the hd case should have it as well as a Chevy with a 231c case.
Comparison of the JB Conversion main shaft and the stock main shaft. The strength gains are pretty obvious in the tail shaft section. I shouldn't have to worry about shearing this one.
On to the build!
First install the input shaft in the planetary gear. There are two plastic thrust bushing type things, a retainer cap, and internal lock ring contained in the planetary. the wings on the thrust bushings and retainer will keep them aligned in the planetary shell. Place a thrust bushing in the bottom of the planetary then the input shaft. You may need to rotate the input as you slide it in to get the pinions to all line up. Then add the second thrust bushing retainer and lock ring.
[
]Should look something like this when you are done.
The input/planetary assembly will slide in from inside out. The planetary will ride in the gear cut in the ring around the inside of the case.
Don't forget the lock ring to hold the input in place.
