Does ANYONE know where I can find a 23 spline NP203 input shaft? Or know how to mate my NP435/NP203?

Hey guys,
This isn't a "WTB" ad for the classifieds. I'm at a loss. I'm at a loss! I have an NP435 Ford transmission, that has an Advanced Adapters kit, to swap it into a CJ7. SO, that means that it has a 23 spline output now, to mate to a Dana 300. I'm trying to shoehorn an NP203 doubler case between the NP203 and the NP435. The NP203 doubler case is set up to run between a Chevy TH-350 and a Dana 300. So, I'm golden on the back end. I've even got a really nice triple stick shifter setup to shift my D300 and the NP203.

After a talk with Advanced Adapters, I realized that the round lip of the NP203 TH-350 adapter will index right up to the round opening of the NP435 adapter! I just need to drill and tap the four mounting holes from the TH-350 to the adapter on my NP435. Hopefully I have lost you yet! So, I can physically mate all of these up as it stands now! I have one last connection to make. That's the output of my NP435 to the input of the NP203.

I'm told that the answer to my conundrum is a '74-'79 Dodge pickup (automatic) NP203 23 spline input shaft. If I can swap out my current (Chevy) 27 spline input shaft with a Dodge (23 spline) input shaft, I SHOULD be in business!

I'm making a full belly skidplate that will have two transmission mounts. I was going to build a crossmember to pick up the existing mount (on the adapter between the NP435 and D300) and another to pick up the transmission mount on the NP203 TH-350 adapter. I'm able to physically bolt up the whole concoction, sans getting the 27 spine female NP203 input shaft to mate to the 23 spline male NP435 output shaft! I feel like I'm SOOO close. I just need to track down one of these '74-'79 Dodge NP203 23 spline input shafts!

I know, I know, I should buy an Atlas. Well, I'm ONE PART away from having this buttoned up! More than anything, I want to get it done, as it will bother me if I give up. I've already re-geared my D300 with 4:1 LoMax gears. Wanting to also run the doubler. I have a dream of a triple sticked, dual cased CJ7 buggy that will crawl super slow! If I can get this done, I'll have basically a 2:1 low range (NP230 in low/D300 in high), 4:1 low range (D300 in low/NP203 in high) and 8:1 low range (NP203 & D300 in low/low).

My NP435 is really short with a case just over 10" long. I'm NOT wanting to run the long Dodge 727/NP203 adapter. I already have these able to mate up, and I'm TOLD that shaft lengths will work out with this setup how I have it. I have plenty of wheelbase. I stretched my CJ7 from the factory 93" wheelbase to 107", AND I have room to go longer in the rear. I'm at 107" leaf sprung front and rear. I'm swapping from the current Chrysler 9.25" leaf sprung rear, to a 14 bolt. I'm going to remove the leafs and 4 link the rear, and put it on coilovers, so I have a lot of room to move the axle back further, if need be. Planning on building my 4 link and ordering driveshafts once I get this project buttoned up. It will be a pretty low powered rig. Factory 4.2 I-6 powered. And going from 37's to 40's. I have a set of 40" Maxxis Trepador Competition Stickies. I run the rig mostly in the south west. Moab, Rubicon, etc. I'd REALLY like to figure out making this setup work, even though there are other solutions (Atlas, etc.).

So, do any of you FINE folks here know where I MIGHT be able to find a 23 spline '74-'79 Dodge NP203 input shaft? OR, perhaps someone has done this same swap and has a better better solution for me? Any help would be GREATLY appreciated!

Also, (just in case this sounds familiar to anyone) I'm building a tube chassis rock buggy, and at one point was talked out of running this setup behind a 5.3 "LS" in the buggy. I AM going to run an Atlas in the tube buggy. BUT, I'm still wanting to figure out getting this setup to work, and planning on running it in my '81 CJ7.

Sorry for such a long post! Thank you to any of you still reading this! And, thanks in advance for any help!

Here's the 'ol Jeep in question:

Whoops, HERE it is:

Lots of work still gonna happen on this rig. 4 link in rear, 3 or 4 link up front, about to start building a full new cage and install new Corbeau front seats. My son really wanted the rear facing back seat. It's a Corbeau bench. He an my wife both like riding back there so much, that I often will find both of them in the back, and no passenger up front with me. Easy in and out, too!

Here's the connection that I'm fighting with:

Is the NP435 same as whats referred to as "Rock crusher" ?? Cuz i removed a crusher from a NP203 as im mating the low end to a NP205 and adapting it to a TH400.

@1-tonmudder here or on other forums comes across cases and parts all of the time. He might have something for you.

If you dont have the doubler parts already, have you thought about going with a 241 based doubler? It would bolt up to your trans, and parts are easier to find.

NeoTech said:

Is the NP435 same as whats referred to as "Rock crusher" ?? Cuz i removed a crusher from a NP203 as im mating the low end to a NP205 and adapting it to a TH400.

Click to expand...

Well, the actual "rock crusher" transmission (as I have been told, at least) was the Muncie 22, which was a performance transmission from the 60's. But, the granny geared truck transmission that I've also heard referred to as "rock crusher" is the Muncie SM465. It was common in the square body Chevy pickups, 1/2, 3/4 and 1 ton trucks. Used by GM from like '68-'91. Not sure what else it was used in. Fairly similar to the NP435.

I was thinking about trying to find a '79-'91 SM465, as they have the 32 spline output shaft, as opposed to the 10 spline output of the earlier ones. That is the same spline as the TH-400, and I have found some 32 spline input shafts for the NP203 case. The SM465 is similar enough to my NP435, though the case is a couple inches longer. 1st gear is really low in both (6.55:1 in the SM465 and 6.68:1 in the variant of the SM465 that I have).

It sounds like you may have one of the '79-'91 SM465's that has the 32 spline output? That's my plan "C". I just rebuilt my transmission, it's installed, and I love it! I would like the SM465 just the same, Id just prefer to not change it.

paradisepwoffrd said:

@1-tonmudder here or on other forums comes across cases and parts all of the time. He might have something for you.

If you dont have the doubler parts already, have you thought about going with a 241 based doubler? It would bolt up to your trans, and parts are easier to find.

Click to expand...

I'll reach out to him, thank you!

Nikwho said:

I'll reach out to him, thank you!

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If he doesn't answer here he's very active on NC4x4.com. He's an old wheeling buddy of mine, a good dude, and the king of all things junkyard.

I'll try to connect with him there, if I cant get to him here. I ALMOST just pulled the trigger on buying a complete '78 or '79 W350, complete with pass side drop Dana 60, but found out it didn't have an NP203.