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Advanced Fabrication and Engineering For when your build is going off the charts. Wildly modified vehicles and straight up buggies welcome.

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  #1  
Old December 4th, 2017, 13:52
XJalltheway85 XJalltheway85 is offline
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NP241OR Rock-trac transfer case parts interchangeability

Hey guys, Iíve been researching parts interchangeability between the different versions of the NP241J. Specifically which parts from a normal 241 will fit a 241OR and the differences between the TJ and JK versions of the 241OR. I couldnít find much info, so I decided to share what Iíve learned.

About a year ago I bought a 241OR from a 2003 TJ Wrangler that had self destructed with hopes of rebuilding it and swapping it into my 2001 XJ. When I got the transfer case home I saw that it was in rough shape, every part of it was damaged including a cracked front case half and the previous owner had disassembled the case himself before selling it. For some reason he decided to disassemble the oil pump housing on the rear case half, which the FSM states to never take apart. At this point I realized I needed a donor transfer case, but I knew how hard it would be to find another 241OR, so I started thinking about the NP/MP241 that comes in the JK Wrangler. I looked on Craigslist and found a MP241 from a 2013 JK Wrangler for $140! I bought it, took it home and started taking it apart. Iíll post some pics for you guys soon.
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  #2  
Old December 4th, 2017, 18:08
XJalltheway85 XJalltheway85 is offline
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Re: NP241OR Rock-trac transfer case parts interchangeability

The first thing to come off the MP241 was the rear bearing retainer. Here is a picture of the rear bearing retainer from my 241OR on the bottom and MP241 on the top. The bolt pattern is the same so these retainers appear to be interchangeable.

Here is a picture of the rear case half from my 241OR on the left and the MP241 on the right. Although they look different it appears they have the same bolt pattern and will interchange with a slight modification of the pocket for the shift fork rail.

Hereís a pic of a 241OR from a JK, recognize the rear case half and rear bearing retainer? I think they are cast in the same mold and just machined slightly different depending on which case they are for.

The MP241 uses the same style oil pump as the 241OR, so that solves my issue with the rear case half. Iíll post pictures of the modification for the shift rail when I find time to do it. Since the 4:1 planetary is unique to the 241OR I knew Iíd need to order the front case half, which was the most expensive piece to this rebuild. I managed to find one on Rockauto for $420 shipped, when it arrived I was surprised to see it already had a bearing and seal for the front output installed.
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Old December 5th, 2017, 07:46
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Anak Anak is online now
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Re: NP241OR Rock-trac transfer case parts interchangeability

Good info. Keep it coming.

I would not worry about taking apart the oil pump and putting it back together. There is nothing magic about that part. There are not any pieces to be replaced inside it, and I think that is why the FSM tells you not to take it apart.

One of the more important preventative fixes I have done on my Suburban has been to take apart the oil pump and replace half of it with an aftermarket piece to prevent it from eating its way through the transfer case (Look up NP246 pump rub and Merchant Automotive if you are curious).

I think the pumps in the NP2xx series cases are all pretty much the same. There is a seal that can be replaced from the outside of the pump, but it is probably safer to reinstall it with the two halves separated. You can also do a better job of cleaning the pump by disassembling it. I wouldn't fret much over someone doing something different from what the FSM states.
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Old December 5th, 2017, 09:12
XJalltheway85 XJalltheway85 is offline
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Re: NP241OR Rock-trac transfer case parts interchangeability

The oil pump that the 241OR and the MP241 use is a different style than what was used in other NP2XX series cases, that is why I couldnít grab a rear case half from just any 241. Here is a pic of the oil pump assembly installed in my 241OR, notice the housing even says ďdo not serviceĒ.

Here is a pic of the rear case half without the oil pump installed. You can see this a much different design than the oil pumps on the past NP2XX series cases.

And this is what the oil pump assembly consists of, two gears and a housing. I have seen this assembly for sale on a couple websites, even thought the FSM says it canít be serviced.

Hereís what the FSM says the issue is with disassembling the oil pump.

The FSM shows no special tool for alignment, it only advises that the oil pump and rear case half must be replaced together. I guess they must use a special alignment tool at the New Process Gear factory when they assemble the pumps.
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Old December 5th, 2017, 15:16
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Re: NP241OR Rock-trac transfer case parts interchangeability

Interesting.

Yes, that one is different. I had not seen one of those before.

Disregard my previous comments. They apply to the NP231 and NP246, but not this case.
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  #6  
Old December 5th, 2017, 15:35
XJalltheway85 XJalltheway85 is offline
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Re: NP241OR Rock-trac transfer case parts interchangeability

Once I opened the MP241 up I was interested to see what internal parts were interchangeable with my NP241OR. The chain and sprockets from the MP241 look like they will work in my NP241OR since they both have the same internal spline count. The sprockets themselves have a different tooth count so you have to swap the chain with them, but both chains are 1.25Ē wide and rocker joint design, so I see no compromise in strength. I came across an old thread on here where someone was selling a NP241OR with an upgraded 1.5Ē wide chain and sprockets, they claimed they were from a NP263. This makes me think that many of the chain and sprockets sets are interchangeable between the NP2XX series cases.
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  #7  
Old December 6th, 2017, 18:39
XJalltheway85 XJalltheway85 is offline
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Re: NP241OR Rock-trac transfer case parts interchangeability

The planetary gear set in my NP241OR was toast when I bought the transfer case, which you know is the most important part of the case since it gives you the 4:1 ratio. Itís also the most expensive part of the case and ironically costs more than a complete working transfer case. I knew I needed to figure out how to rebuild my planetary since the gears still appeared to be in good condition but just had a ton of side to side rock in them due to worn needle bearings and missing plastic spacers. I started thinking about where I could find new needle bearings, spacers, and axles for my planet gears and I realized that I could probably find them in a planetary from another NP241. So I went to the Pull and Pay and bought a six pinion planetary out of a NP241C and took it along with my 4:1 planetary to a transmission shop near Denver. This is what I got back.

The guys at the shop said it was more of a pain then they expected, but they were able to get my 4:1 planetary rebuilt using the parts from the 241C planetary. The axle pins for the 4:1 gear set are actually shorter than the ones from the 241C so they had to grind them down and tack weld the ends of the pins instead of steaking them. Hereís a pic, 4:1 on the left, 241C on the right.
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