NP203 to NP208 swap?

[iamtherealJayy]

I have a 1976 Chevrolet K10 with a 350 and I believe TH350, it has an NP203 tcase that I want to eliminate for better fuel mileage(truck is being built to be a cruiser that can drive wherever whenever) i recently traded off my 1981 Frankenstein for an 86 k10 Silverado and an 80’s k20 frame. The k10 didn’t come with a title and it has a 305, so parts truck. Would the np208 from this truck swap directly into the th350? Or would I have to swap the entire trans/tcase/crossmember assembly? I’ve got both entire trucks, both running and driving and I want to combine them, I just don’t know the interchangeability. I assume possible driveshaft swap and I figure the 203 hubs will have to be swapped to the other hubs. The 86 np208 has “4x4” hubs not lockable hubs. If the 203 had better fuel mileage and didn’t eat front tires id keep it but because I do plan on being able to drive this truck frequently I want it to be more enjoyable and have a 2wd option.

 

[Bextreme04]

You can try to just convert the 203 to part-time? That would be the easiest solution, otherwise you will be best off to swap trans and t-case. An 86 K10 would have been a 700R4/208 combo most likely, so you would get a better part time transfer case AND an overdrive gear.

 

[iamtherealJayy]

I’m assuming you mean trans and tcase I’m not swapping in a 305 lol. If I could find a simple enough part time conversion I’d do that. I just want a 2h option for highway driving.

 

[Big Ray]

I have a 79 K5 with a th350 and 208. It has manual hubs but still only gets 10 mpg.
I bought a 208 for it. It's my springtime project.


Th 350 & 700r4 both have 27 spline output shafts. A 208 from a 1/2 ton will work fine.
Driveshaft, you'll find out when you get there.

 

[iamtherealJayy]

I’d originally bought this truck in July for my ole lady so she could have a truck to do truck things I guess? Hell I don’t know she said she wanted one. Anyways she’s not gonna be 4 wheeling or anything crazy, yes it’s got aggressive mud tires and wide wheels but it will rarely leave the pavement. I plan on making it my daily driver while rebuilding my 87 from the ground up and ls swapping my work truck since the 350 is about ready to croak.

 

[Big Ray]

208 is a good t/c. Drive it with some common sense and it will last.
It was good enough for the Armys CUCVs.
I have another truck getting a nv4500 and new motor. It'll have a 208 behind it.

 

[iamtherealJayy]

I’ve got a 208 in my 87 v20 and it’s my favorite out of the three I’ve had. My 205 won’t come out of 4x4 unless I slip the clutch and move slightly. And the 203 I’ve just heard too much negative about it.

 

[bucket]

I have a 79 K5 with a th350 and 208. It has manual hubs but still only gets 10 mpg.
I bought a 208 for it. It's my springtime project.


Th 350 & 700r4 both have 27 spline output shafts. A 208 from a 1/2 ton will work fine.
Driveshaft, you'll find out when you get there.

Yes, the th350 and 700r4 both have 27 spline outputs, but the output for use with a 203 is much shorter than what was used with a 208.

 

[Big Ray]

I like being able to use 2wd, vs 4wd with an unlocked axle. It is a tank though, never heard of one breaking.

 

[iamtherealJayy]

If I’ve got the driveshafts from the 208 and the cross member etc would it work together? Or is it enough difference to not interchange

 

[Big Ray]

Yes, the th350 and 700r4 both have 27 spline outputs, but the output for use with a 203 is much shorter than what was used with a 208.

That, I did not know. Thanks

 

[bucket]

That, I did not know. Thanks

I'm curious about yours though. The factory 350/208 combo is relatively rare. Super common for '81 of course, but most 4x4's '82 and up were optioned with the 700r4. Does yours have an aluminum spacer between the trans and t-case adapter? If so, it's probably a short tail 2wd th350.

 

[Big Ray]

Mine is a th350/203.
I'm swapping to a manual/208 this Spring. 4 speed overdrive.

 

[bucket]

Mine is a th350/203.
I'm swapping to a manual/208 this Spring. 4 speed overdrive.

Ah, I misunderstood. I don't always read well, lol.

 

[bucket]

I've been contemplating a 4 speed overdrive swap in my '77 K5 as well, but using the 203 from my K30 and redrilling the face so it bolts up.