I I would really like a turbo 400 in my truck

[jakewalter]

I have a 85 K20 that I built up to haul our 3500 pound pickup camper.

It currently has a pretty healthy big block that I built for torque.

The transmission is a 700R4 and a 208 transfer case.

While on vacation a couple of weeks ago the transmission started slipping and I lost reverse.

I never use the overdrive and as for mileage I threw my pencil away a long time ago.

Other than a TH400 out of a 4wd what else would I need?

I would really appreciate any input that you guys could share with me.

I need to apologize.
The guy that rebuilt my transfer case said that it is a 208 not a 203.

[Accelo]

The correct adapter plate for the 400. The 700R4/4L60 uses the same bolt pattern as the THM350.
You also need to have the modified THM 400 input shaft on the 203. It typically requires re-boring for the larger bearing required for the larger THM 400 output shaft.
Edited
Sorry, I confused the 203 and 205 boxes

[Dead Parrot]

The electric kick down switch. Early versions were set on the intake behind the carb. When cable throttles happened, the switch moved into the cab.

[kwmech]

203 transfer cases do not have to be bored out, they already have the 210 bearing in them, you will need the 400/203 adapter and a 32 spline input gear for the gear box and have it swapped in--which is a chore in itself---not hard but time consuming as you have to separate the 4x4 chain box from the low range gear box. If you decide to go through with this I should have the parts sitting around here somewhere.


Looks like OP edited his parts. Same still holds for parts. Adapter and input gear, but also the 400 needs the proper output shaft for the thickness of the adapter. The 208 is a lot easier to rebuild. I do not have a gear for the 208, but they can be had for about 100-120 dollars, plus a good time to rebuild it with new bearing, fork pads and a chain. I have an adapter and possibly the output shaft needed for the 400

[jakewalter]

Originally Posted by Accelo

The correct adapter plate for the 400. The 700R4/4L60 uses the same bolt pattern as the THM350.
You also need to have the modified THM 400 input shaft on the 203. It typically requires re-boring for the larger bearing required for the larger THM 400 output shaft.
Edited
Sorry, I confused the 203 and 205 boxes

I need to apologize.
The guy that rebuilt my transfer case said that it is a 208 not a 203.

[jakewalter]

Originally Posted by Accelo

The correct adapter plate for the 400. The 700R4/4L60 uses the same bolt pattern as the THM350.
You also need to have the modified THM 400 input shaft on the 203. It typically requires re-boring for the larger bearing required for the larger THM 400 output shaft.
Edited
Sorry, I confused the 203 and 205 boxes

Originally Posted by kwmech

203 transfer cases do not have to be bored out, they already have the 210 bearing in them, you will need the 400/203 adapter and a 32 spline input gear for the gear box and have it swapped in--which is a chore in itself---not hard but time consuming as you have to separate the 4x4 chain box from the low range gear box. If you decide to go through with this I should have the parts sitting around here somewhere.

Looks like OP edited his parts. Same still holds for parts. Adapter and input gear, but also the 400 needs the proper output shaft for the thickness of the adapter. The 208 is a lot easier to rebuild. I do not have a gear for the 208, but they can be had for about 100-120 dollars, plus a good time to rebuild it with new bearing, fork pads and a chain. I have an adapter and possibly the output shaft needed for the 400

I need to apologize.
The guy that rebuilt my transfer case said that it is a 208 not a 203.

[cadillac_al]

The 203 is my favorite transfer case and those are the only trucks that I buy. I would take the easy route and go with the bulletproof 203.

[Getter-Done]

Your ideal setup IMHO would be.

A combo of T400 with a 205-transfer case.

Any change will require driveshaft modifications.

The 205 transfer case is (All Gears) the toughest.

The 203 Transfer case is (what I have always had) has a Chain drive.

The 208 Transfer case has an Aluminum case.

If you study this website in the link below about the adapters, it will give you a better idea.

Link: https://www.advanceadapters.com/

[v30crewcab]

you can also hunt up a 32 spline 241. they were in the 88-91 suburbans, and are pretty strong.

[kwmech]

Originally Posted by v30crewcab

you can also hunt up a 32 spline 241. they were in the 88-91 suburbans, and are pretty strong.

Really hard to find though

[cadillac_al]

Didn't those military CUCV trucks have th400's and 208 transfer cases? There must be a few of those coming up for sale from time to time.

[franken]

As I recall in the late 80s and/or early 90s GM put a TH400/NP205 setup in trucks. Pretty rare but its another option if the 1.96:1 low of the TC is ok.

[THI]

I have a TH400 with a 32 spined output for a 208/241 along with the adaptor that I will not be using. The trans was rebuilt about three years ago and sitting in heated storage since due to health reasons. It is in a storage building near Empire.

[kwmech]

Well there ya go.

[THI]

I even have the kickdown switch and wiring.

[GRADYS Performance]

Not quite as easy, But what about swapping a 4L80. Strength of a TH400. With Overdrive and a Lockup torque converter.

[jakewalter]

Originally Posted by THI

I have a TH400 with a 32 spined output for a 208/241 along with the adaptor that I will not be using. The trans was rebuilt about three years ago and sitting in heated storage since due to health reasons. It is in a storage building near Empire.

PM sent

[cadillac_al]

I don't think Jake's 208 has the 32 spline input. It shouldn't be that hard to buy one though.

[kwmech]

Originally Posted by cadillac_al

I don't think Jake's 208 has the 32 spline input. It shouldn't be that hard to buy one though.

Input gear can be swapped out with a rebuild/refresh easily enough

[jakewalter]

Good morning everyone,

I would like to thank all of you for your advice and input.

I have decided to rebuild my NP208 and replace the input shaft to a 32 spline.

Now I need to find a good place to order the rebuild kit and the input shaft.

Any thoughts would be appreciated.

I don’t mind paying the extra cost for quality parts.

Thanks so much,
Jake

[kwmech]

https://www.offroaddesign.com/transfer-case/np208.html

[Getter-Done]

https://torqueking.com/category/1981...transfer-case/