NP203 to NP208 swap?

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
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

Full Access Member
Joined
May 13, 2019
Posts
4,135
Reaction score
4,983
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
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.
 
Last edited:

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
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

Supporting Member
Supporting Member
Joined
Oct 14, 2022
Posts
1,221
Reaction score
4,144
Location
North Carolina
First Name
Ray
Truck Year
1979
Truck Model
K5
Engine Size
400
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

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
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

Supporting Member
Supporting Member
Joined
Oct 14, 2022
Posts
1,221
Reaction score
4,144
Location
North Carolina
First Name
Ray
Truck Year
1979
Truck Model
K5
Engine Size
400
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

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
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

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
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

Supporting Member
Supporting Member
Joined
Oct 14, 2022
Posts
1,221
Reaction score
4,144
Location
North Carolina
First Name
Ray
Truck Year
1979
Truck Model
K5
Engine Size
400
I like being able to use 2wd, vs 4wd with an unlocked axle. It is a tank though, never heard of one breaking.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
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

Supporting Member
Supporting Member
Joined
Oct 14, 2022
Posts
1,221
Reaction score
4,144
Location
North Carolina
First Name
Ray
Truck Year
1979
Truck Model
K5
Engine Size
400
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

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
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

Supporting Member
Supporting Member
Joined
Oct 14, 2022
Posts
1,221
Reaction score
4,144
Location
North Carolina
First Name
Ray
Truck Year
1979
Truck Model
K5
Engine Size
400
Mine is a th350/203.
I'm swapping to a manual/208 this Spring. 4 speed overdrive.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
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.
 

Latest posts

Forum statistics

Threads
41,847
Posts
903,383
Members
33,362
Latest member
Dhatch84
Top