Looking for info on a TH400/NP205 Swap

[handloader90]

I have a 1986 Jimmy that I'm going to build up. It has a TH350/NP203 and 10 Bolts front and rear.

I'm picking up a CUCV set Dana 60 and 14BFF with 40K on them next weekend.

I want to run a TH400 and NP205 behind my engine.

For the TH400 am I better off getting one from a Military (CUCV) or Civilian truck? What are the identifiers/ differences between the two?

For the NP205, what exactly am I looking for? I know it has to be the large bearing to bolt up to the TH400. What are the identifiers that I'm getting the correct NP205?

 

[sweetk30]

torqe convertor and govoner are different on cag to diesel .

some have bolted them in and just changed the govoner and been happy .

and 205 is 32 spline female input to be behind th400 . there was 2 input lengths and adaptors to match the correct tail shaft length .

and fyi th400 over th350 eat's up 20-25 hp over a th350 .

I ran a th350 built that was built up for years on a health 400sbc and 4.10 gears in 1tons and 38" swampers . never a 1 problem .

might be faster for you to just swap the t-case on he th350 you got and bolt the 205 on . they use the same tail shaft on tranny in th350 . I have the adaptor / input / coupler sleeve to fit a 205 on a th350 in the sale section . and you could pickup a cheep 10 spline 4 speed 205 and regasket it after you swap the input gear . easy job to do .

 

[Hogback Fabrication]

I could write a book on the subject, but the reality is that you are MUCH better off finding a TH400 and 205 that are together rather than trying to get them separate and then making them mate together. Time/money ahead.

 

[diesel4me]

I've had at least 3 TH350's in 4x4 trucks,behind 350's,a 400SB and a 454,all of them held up darn good ,and they got a beating plowing and one truck I used to commute 70 miles each way to work daily..only the one behind the 400 SB lost reverse eventually,and it had been behind a 454 for a long time before I bought the truck and swapped the 400 SB into it..losing reverse seems to be the first thing to "go" on them...

I like TH400's and have had quite a few in cars,like my '69 GTO,but the 82 GMC is the only 4x4 truck I have had with one,and its a 2wd or car version ,it doesn't have the "K" case with the cast cover over the flywheel the strut rids bolt too--despite that it has survived almost 12 years of abuse plowing and now daily driving,and it still shifts just as firm as it ever did..they may suck up a few more HP,but they are larger inside and have bigger clutches ,so they can handle more torque than the TH350..but they aren't a "must" either really..

I'm not a fan of 700R4's,but the overdrive is a plus ,especially if you have a diesel,or do a lot of highway driving..they dont seem to last long in stock form though,if you rebuild them with the right heavy duty parts they are OK,but you could probably buy 2 TH350's or TH400's and slap them in and go for less money...personally I dont care if I lose 5 mpg not having overdrive..

The old NP-203's aren't a bad transfer case,they get a bad rap for being "full time" and heavy ,being cast iron,but they usually live a long time with no major problems..they "waste gas" but sometimes having the full time 4wd will save your butt in certain situations..

It's nice to have all the "bullet proof" stuff like a NP-205,a good tranny,and a Dana 60,but I wonder how many of us really need that in the long run...I've plowed just as much snow with 1/2 tons with "wimpy" 10 bolts and never broke them,and I didn't baby them either...

 

[63chevyll]

I could write a book on the subject, but the reality is that you are MUCH better off finding a TH400 and 205 that are together rather than trying to get them separate and then making them mate together. Time/money ahead.

Your right.

But hey, why not a 700r4 and a 241 combo.

Overdrive for the highway, and a better LO range ratio. Plenty available.

Yes the 400 and 205 are pretty damn strong, but I guess is also.defends how your gonne use your rig

 

[handloader90]

So what I'm getting from all of this is get keep the TH350 and just get a Np205 for it?

My TH350 is of the Non-Lockup kind, I checked it all over and didn't find any kind of ports or wires coming out of it.

I don't do much highway with my squarebody's and my work commute is 10 minutes give or take. So I'd honestly rather not have an overdrive.

So with me keeping the TH350 what am I looking for in the correct NP205? Spline count, female/ male, small bearing etc.? What all am I going to need, just the adapter and the sleeve connecter?

Another question, I'm looking to run the same setup on both of my squarebody's for interchangeability reasons. When I search for my next 4x4 TH350, what's gonna be the best one, Like one with the "HD" stamp or "K" stamp on the case, any other identifiers?

 

[diesel4me]

A TH 350 has 27 splines on the output shaft--so does a 700R4...the TH400 has 32 splines...(as does a 82-up SM465)...GM made so many different lengths of output shafts I agree its easier to buy a trans with a T-case already coupled together,that way you know they are compatible...

I'm not sure,but I think a TH350 that was coupled to a NP-203 T-case has a shorter output shaft than one that would couple up with a NP-205 t-case..2wd trucks and cars have several different length outputs available,I think they are 6",9",and 12"...the 4x4 versions are "stubby" and in most cases if you want to use a car or 2wd tranny in a 4x4 ,you'll need the correct 4x4 output shaft for the particular t-case your using--also there are adapters between the tranny and t-case that are specific....to use a 2wd tanny in most cases,you'll have to "gut" the tranny and put that shaft in it--its the first piece in and the last one out,so a total rebuild might as well be done if you go that route..

The "K" cases are stronger,but in my opinion probably not that much...there are some TH350's that had more clutches than others,one meant for use behind a straight 6 or 305,or V-6 will likely be the lighter duty version,compared to those put in heavier vehicles with larger engines..you can look up the codes on the tag on the case and use a factory manual to identify which version it was..

The TH400's have a lot of variations on output shaft lengths..in most cases the 4x4's had a specific output shaft ,and adapter between the tranny and t-case for the particular t-case your using..this is why buying a "used matching pair" is best,it avoids all the headaches..