th350-np203 to th400 np205 swap

[wazzabie]

My 78 k5 came with the th350-np203. I have swapped out the np205 and adapter with a np205. So now i have the th350-np205. I did not need to change the cross member. Now I would like to go to a th400-NP205. Would I need to change me cross member?

 

[Hogback Fabrication]

Depends on the adapter you're using.

Your K5 needs a crossmember from a 1/2 ton or 3/4 ton truck (the 1 tons had taller frames that used crossmember with less "drop").

If your TH400/205 adapter is the figure 8 pattern on the 205 ('84 and older) then your t-case mounts and crossmember will work.

If the adapter is the later round pattern adapter ('85-90, would use a completely different 205 than you have), you'd need a different crossmember and mounts.

 

[70jimmy]

Crossmember should be useable but will need to be moved back some. because the 400 is a little longer tranny.

 

[wazzabie]

Crossmember should be useable but will need to be moved back some. because the 400 is a little longer tranny.

Would this then require drilling holes in the frame and/or cross member?

 

[Hogback Fabrication]

Would this then require drilling holes in the frame and/or cross member?

4 new holes in the frame

 

[wazzabie]

Any way I can get away with a 350-TH400-NP205 with out having to drill the frame in a 78 K5?

 

[Hogback Fabrication]

Any way I can get away with a 350-TH400-NP205 with out having to drill the frame in a 78 K5?

You could probably make that happen with a custom made crossmember. But no matter what you do, the TH400 is longer than the TH350 and the adapters are about the same length, so the t-case mount gets moved further back.

 

[dremu]

Any way I can get away with a 350-TH400-NP205 with out having to drill the frame in a 78 K5?

It's what, four holes on the bottom of the frame, easy to drill. Just do it.

-- A

 

[82355]

Why not just leave the TH350 in there? The NP205 that you have behind the TH350 will not work with the TH400.

Martin