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Discussion Starter #1
Has anyone tried to adapt a Getrag 2wd mainshaft or a nv 4500 Dodge Cummins 2wd mainshaft to a np 203? I'm not sure if it will work, but the Dodge 2wd shaft is listed as a 31 spline, which is the same as ford input shafts, but are they the same diameter? I don't have these parts in front of me to test, has anyone else tried this. I'm also thinking the mainshaft could be resplined and shortened to couple to the Ford np 203. I'm trying to do a doubler with a Cummins, and would like to use a Dodge fully splined mainshaft. Thanks in advance.
 

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You need a dodge nv4500 case, cummins input shaft, gm 32 spline 4x4 output shaft, and gm 4x4 tailhousing. Find or buy the 32 spline input for the 203, put it all together and drill and tap your mounting holes into the face of the 203 (its easy the 203 seal housing indexes the 4500 tailhousing).
 

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Discussion Starter #3
I know I can use the GM 32 spline shafts but I have not found one that is fully splined like the ones behind the Cummins and I have lost 5th gear twice in one of my other trucks. I've been told that the GM diesels never had a problem with 5th gear coming off, so the shaft design was never upgraded like the Dodges. I would like to hear from someone with a 32 spline nv 4500 behind a Cummins and how many miles it will hold for.
 

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I know I can use the GM 32 spline shafts but I have not found one that is fully splined like the ones behind the Cummins and I have lost 5th gear twice in one of my other trucks. I've been told that the GM diesels never had a problem with 5th gear coming off, so the shaft design was never upgraded like the Dodges. I would like to hear from someone with a 32 spline nv 4500 behind a Cummins and how many miles it will hold for.
This contradicts its self, If you have a gm 32 spline output with a doubler (i do) why are you concerned about miles or towing? Dual cases are generally utilized off road where high mileage and towing are not an issue. The only reason 5th gear is an issue is because after towing in 5th the nut will work its way off. Unless your planning on running the trails all day long in 5th gear there is not an issue.

I have been running the 32 spline doubler setup for a while on it and it holds up to some abuse.
 

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Discussion Starter #6
I plan on putting a lot of highway miles on this truck along with off road miles so I think 5th will get a lot of use, probably some hauling/towing too. Is there another 241/205 doubler other than the black box?
 

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I plan on putting a lot of highway miles on this truck along with off road miles so I think 5th will get a lot of use, probably some hauling/towing too. Is there another 241/205 doubler other than the black box?
You are confusing the Black Box with the 241 doubler. They are not the same. The Black Box is similar to a Klune V and mounts between the transfer case and transmission. The 241 doubler is where you take a 241 and cut the front half of the housing down, weld in a filler, add the adaptor plate, etc to mount another transfer case to what's left of the 241.
 

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I plan on putting a lot of highway miles on this truck along with off road miles so I think 5th will get a lot of use, probably some hauling/towing too. Is there another 241/205 doubler other than the black box?
Pics of said highway/doubler canidate?
 

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Discussion Starter #11 (Edited)
I have looked into the doublers and the Black Box and I like the Black Box because it will bolt in easy, lighter weight, and lower ratio than a 203. What does it take to break a 241/B.B. style planetary? Does it basically come down to the input and output shaft size being the weak link in the smaller shaft sizes? I would be using a 29 in and 31 out and I don't think they will ever be a weak link. I haven't spent the time to figure out how to post pics., but I will try to soon. I am building a 1947 Power Wagon, 4BT, Getrag or nv 4500, 205 with doubler, D70 rear disc, D60F , 4.10 gears. I've been gathering parts for years and I'm putting it together now.
 

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Your best bet is going to be to go with a 241/205 doubler. The weak link in the 241 is the aluminum case, when you use just the planetary part, you get rid of a lot of that weakness.

The plus is it all bolts up to the nv4500 and it is way cheaper than going the black box route.
 

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I built a 241/241 doubler for mine when I installed the 6.5 Detroit/4L80e a few years ago. Like you I wanted highway friendly axle gears, but still wanted a good crawl ratio.

I drove mine nearly daily for about 10k miles before the next engine swap with zero issues, so I believe it's going to be ok. If you have descent mechanical skills they are fairly easy to build yourself if you want to save a little cash. Here is a link to how I built mine if your interested.

http://www.s10forum.com/forum/f222/how-i-built-my-doubler-387431/
 

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Discussion Starter #14
Thanks for the info, I looked at the 241/241 build link and that is a good build, well done and good tech. info. I'm still not sure which route I'm going yet. I will keep you guys posted on this and some pics. eventually.
 
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