TH400 to NP203 help...

[zj4play]

I tried to do a search but couldn't find the info I was looking for. I am wanting to put a TH400 in my 1974 blazer that currently has the TH350/350/NP203 combo. Anyone know how many splines are on the input shaft of the NP203? 10 or 32? Do I need a special adapter to mate them? Or do I just get a new output shaft for the TH400 that matches the NP203? As you can tell, I know nothing about transmissions and transfer cases so thanks for the help hopefully.

 

[4X4HIGH]

A TH350 has a 27 spline output
A TH400 has a 32 spline output

You would need a TH400/203 adapter (hard as hell to find) then swap the 27 spline 203 input gear in favor of a 32 spline input gear, and then you need to make sure the TH400 has the correct length output shaft of 1 3/8" from the end of the case, then you need to have the front driveshaft lengthened and the rear driveshaft shortened.

 

[zj4play]

Great info...thanks so much! When you say "hard as hell to find", whats your definition of hell? ORD sell something like that? The only reason I am doing this is I don't think my TH350 is going to stand up to the new motor I am putting in soon. I already figured on the new driveshafts. Thanks

 

[sweetk30]

a well built th350 will hold just fine if kept cool .

i would take a th350 first as its slightly better ratios in the gears and eats less hp over th400.

you can get the parts for the swap but i would look for a whole take out setup in craigs list or ebay near you to get the th400 / 203 you want.

also use this www.craigslook.com sweet tool for craigs list surfing

 

[76zimmer]

I don't think ORD sells the T400/203 adapter, but sometimes they are available in the for sale section. I think that adapter was only available in 77-79 trucks.

 

[zj4play]

Thanks for the input guys...very helpful. I was going to do the TH400 swap because I have one laying around and since I would have to take out my TH350 to go through it and install a new converter, I just figured why not spend that money on the bigger TH400 instead. But if its a serious hassle, maybe I will just leave it in till I can afford the TH400/205 swap? I have a new motor going in the blazer in a few weeks and didn't think the TH350 would hold up.

Oh, and sweetk30...that craigslist thing is pretty cool. Never knew about it.