Can you change TH400 spline?

spicker · Oct 9, 2006

I have a TH400 trans from a 76 wag, it has a 10 spline shaft in it. Can I change it to a 32 spline shaft from another TH400 from GM?

Thanks for all the in put! I am putting a dana 20 t-case behind it. which of the three shafts ( short or long) would I need? Who make the best trans to t-case adapter?

junkyard jim · Oct 9, 2006

Not only can you, but I happen to have that shaft for sale for $20.

TreeClimber · Oct 9, 2006

Been there, done that. In my YJ, have a GM shaft in an AMC case (you need the GM shaft to use an ATLAS).

Things to keep in mind, are that GM used lots of output shafts, with different lengths, the two wheel drives are LOOOONG, and the 4x4s come in at least two different lengths, about an inch difference. Atlas makes a one inch spacer if you've got the longer one, but I found the shorter one, so I was good.

Other things to keep in mind, is that the AMC case is rotated (twisted) like 6 or 7 degrees. What I mean, is that the bolt hole line ups for the Tcase are not the same between AMC and GM. So when you install the adapter for the Tcase, your tcase is not mounted straight, but rather down 6 or 7 degrees. Not a big deal, because most aftermarket adapters allow for 4 different clocking positions. However I had to build a shim, so that the rear tranny support would mount flush to the skid plate.

junkyard jim · Oct 9, 2006

I also have a short cast iron TH400 to NP tcase adapter (supposed to have come off a Humvee with 6.2L TH400 and NP208) for $75

mudracer · Oct 9, 2006

there are three different length output shafts for th400 to 4x4 transfer cases.

NP203 is the shortest.
NP241/np208 is an inch longer
np205/dana20 use the same length shaft, and the Dana 20 shaft must have the bolt hole in the end drilled and tapped into the shaft to retain the gear.

For cheap guys like myself, you can use any car trans with the short tailhousing, remove the tailhousing, and bolt up the trans to an NP205 or dana 20. just make sure if youre bolting it to a dana 20 that you have a boltyoke output shaft *it has the hole drilled and tapped.

I think I have some pics that may help with this identification....

oh, as for the adapter that came from a th400/np208 in a hummer... yeah, it also came from a suburban with that combo, from any 87 or newer 3/4 ton with a th400 and np241 as well. its not uncommon.

attached are the 3 different length 4x4 shafts, not counting the 10 spline jeep shaft.

junkyard jim · Oct 9, 2006

mudracer said:
oh, as for the adapter that came from a th400/np208 in a hummer... yeah, it also came from a suburban with that combo, from any 87 or newer 3/4 ton with a th400 and np241 as well. its not uncommon.

Note that mine is cast iron and not aluminum. It's also shorter (length and height) than the aluminum ones I have seen so far.

mudracer · Oct 9, 2006

junkyard jim said:
Note that mine is cast iron and not aluminum. It's also shorter (length and height) than the aluminum ones I have seen so far.

maybe Im missing something... Ive never seen an aluminum one for a th400. All of the aluminum ones that I have seen are for the 4l60e late model stuff with the removable bellhousing. From what I know, and thats limited these days, they may not match up.

I used this same *(cast Iron) adapter when i built my th400 and ford NP205 combo. I used the early short np205 input, put it in a ford housing, and redrilled the face of the Ford NP205 for the cast iron adapter. The trans mount pad on it requires the 87(*edit: I should have said 88) and later transmission mount for a 4wheel drive. it is the same length, shape, and has the same appearance. all the bolts line up, and it works.

If you want to call your parts hummer parts, fine. They were used on a hummer too.

junkyard jim · Oct 9, 2006

I see you changed pics. The first one showed the piece that goes between the trans and tcase as an aluminum part. And 2wd at that. (this new pic does too)

mudracer · Oct 9, 2006

junkyard jim said:
I see you changed pics. The first one showed the piece that goes between the trans and tcase as an aluminum part. And 2wd at that. (this new pic does too)

I did change photos, to give you an idea of WHERE to find the shaft a person would need. I am not saying that you could use a 2wd tailhousing on a 4x4... i noted specifically that you can use the same trans:

For cheap guys like myself, you can use any car trans with the short tailhousing, remove the tailhousing, and bolt up the trans to an NP205 or dana 20.

I figure common sense would require removal of one before the installation of the other. I should have probably specified th400 car trans, as well, i guess.

I apologize for hijacking this thread with an argument about a part.

The answer you are looking for, spicker, is yes.

Just be aware that you dont have to spend an arm or a leg to get parts, since they already exist.

Jason C · Oct 9, 2006

junkyard jim said:
I also have a short cast iron TH400 to NP tcase adapter (supposed to have come off a Humvee with 6.2L TH400 and NP208) for $75

We have had almost every style of the factory T400 circular bolt pattern bust all to hell and end up using the AA adapter which holds up fine. the only one still living is mine and it is a real oddball with alot of extra bracing and is a long foot adapter. I have never seen another like it. so oyu may be saving a few $$ right now but if your out of state and you adapter comes apart it may end up costing you a trip. Ask Shifty and neckster.

TreeClimber · Oct 9, 2006

If I remember correctly, Novak Adapters also build a billit alluminum replacement for the GM TH400 to Dana 20. The factory one is notoriaously weak.

Novak Adapters has a info page with lots of good stuff on it.

T

spicker · Oct 9, 2006

Thanks for all the in put! I am putting a dana 20 t-case behind it. which of the three shafts ( short or long) would I need? Who make the best trans to t-case adapter?

TreeClimber · Oct 9, 2006

spicker said:
Thanks for all the in put! I am putting a dana 20 t-case behind it. which of the three shafts ( short or long) would I need? Who make the best trans to t-case adapter?

Both Novak Adapters and Advance Adapters are quality. Call them directly and match the output to the adapter.

http://www.novak-adapt.com/catalog/kit_124.htm

http://www.advanceadapters.com/jeep.html

Remember however, that the 20 isn't as wide as most t-cases, and you'll have a clearance issue with the front driveshaft around the belly of the transmission (pan area). The factory solved this with a very skinny front drive shaft (which I may still have one lying around). You could also use a carrier bearing and a two piece shaft....

spicker · Oct 9, 2006

Thanks for the help novak looks like thay have a good kit thank again Tree Climber

mudracer · Oct 10, 2006

you might try upgrading the 20 with bigger yokes, if you want to keep driveshaft u joints around. There are some available, I think.

crash2 · Oct 10, 2006

As jason C suggested--go with a GOOD adapter. We had 2 of them bust down at the hammers (both shifty(ebp) and neckster(trevor) )

junkyard jim · Oct 10, 2006

Jason C said:
We have had almost every style of the factory T400 circular bolt pattern bust all to hell and end up using the AA adapter which holds up fine. the only one still living is mine and it is a real oddball with alot of extra bracing and is a long foot adapter. I have never seen another like it. so oyu may be saving a few $$ right now but if your out of state and you adapter comes apart it may end up costing you a trip. Ask Shifty and neckster.

That was a TH400 to D20 from an FSJ, right? Those were known for their weakness from the factory. Aluminum casting in a poor alloy that was barely engineered to fit.

mudracer · Oct 11, 2006

spicker said:
Thanks for all the in put! I am putting a dana 20 t-case behind it. which of the three shafts ( short or long) would I need? Who make the best trans to t-case adapter?

Of the three output shafts, you will need a bolt yoke style output from a fullsize truck application. This will have the threads machined inside the end for the bolt that retains the gear on the shaft *(or in the truck application, it retains the yoke). It is the longest of the three, pictured on the previous page.
there should be a shoulder on it to retain the gear as well, or you may be able to use the snap ring groove on the shaft.

Jason C · Oct 11, 2006

spicker said:
Thanks for all the in put! I am putting a dana 20 t-case behind it. which of the three shafts ( short or long) would I need? Who make the best trans to t-case adapter?

I think Shifty (EBP on here) has a t-400 to d-20 adapter assembly at his house collectiong dust.... alla fter market I think a Novak.

Jason C · Oct 11, 2006

junkyard jim said:
That was a TH400 to D20 from an FSJ, right? Those were known for their weakness from the factory. Aluminum casting in a poor alloy that was barely engineered to fit.

No what you have a picture of is the same as a t-400 to 208 adapter. one of th eholes is out of sinc to match a 300 or atlas circular bolt pattern. all of the styles have been broken (except mine which for some odd reason is completely different than any of the others we have seen) including the pic of the style you where showing in your pics. the long foot style I have I still would not reccomend to anyone since so far I "may" have been lucky. so lucky that it broke the ass end off my turbo 400 instead of breaking the adapter! UBER COOL! :Good: