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Old 03-23-2006, 08:58 PM
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Transfer case - NP 203 - 205

I'm planning on converting my NP 203 transfer case to part time 4wd. When I do this, I need to also either replace the existing case, or just the chain (since the chain is worn) Has anyone switched theirs to a NP 205? If so, will it bolt right in? I'm guessing that I may have to change the front and rear drive shafts to fit? Anything else? Should it bolt right in?

Thanks again,
Steve

PS It's a:

'79 chevy k10 truck
350 engine
th 350 tranny

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Old 03-24-2006, 06:50 AM
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I will only directly bolt in if it came from another TH-350, and you have the correct adapter plate and shaft sleeve. If so, the shifter will fit into the same hole in the floor and you can use the same shifter boot.

The front driveshaft "should" fit just fine, and I am unsure about the rear.
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Old 03-24-2006, 07:36 AM
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I’m over tired and didn’t feel like pulling out just the stuff you need so I dumped it all here. Some of this info should help.

Bolt Pattern:
All GM NP205 cases 1971-1985 had a 8 bolt "racetrack" bolt pattern
All GM NP205 Cases 1986-up had a 6 bolt circular bolt pattern

Input Spline: GM Used four different input shaft configurations on these cases.
10 spline: (1971-85) The most common were units supplied with a 4 speed which typically had a 10 spline male input shaft.

27 spline: (1971-79) The units supplied with a T350 automatic have a 27 spline male input shaft.

32 spline (Short); 32 spl (Long): The units supplied with a T400 Automatic (also SM465 86-up) have a 32 spline female input. We have seen both a short (about 1.5 to 2.0" stickout) and long (more like 3-3.5" stickout) versions of this gear. This gear is directly compatible with the Klune-V Extreme Underdrive, which can be supplied with a 32 spline output shaft. Longer spacers are required with the long input.

Also see data on swapping input gears lower on this page.
1979 to 1985 GM NP205: 8 bolt "racetrack" bolt pattern:
During these years, the GM NP205 showed up behind Turbo 400 and SM465 Transmissions in 1 Ton trucks only.. 1/2 and 3/4 T trucks began to be supplied with the NP208 instead. SM465 units will still typically use the 10 spline input. Turbo 400 units have the stout 32 spline female input (in most cases the short 32 spl input, about 1.5-2.0" stickout) however still uses the 8 bolt "racetrack" bolt pattern.

Chevy, Dodge and Ford all used variations of this transfer case. All were chain drive to the front output. Some were full-time 4WD while others were part time. While the whole case is very large heavy and clunky, they have attained popularity through the use of the front "range box" section which is then adapted and mated to the front of another transfer case, a dual transfer case setup commonly known as a "Doubler".
Transfer Case Specifications:
Low Range reduction ratio: 1.96:1
High Range: Direct (1:1)


Chevy 203

Input Spline: GM used three different input spline configurations on these cases.

10 spline: (1971-79) Used behind SM465 transmissions

27 spline: (1971-79) The units supplied with a T350 automatic have a 27 spline female input shaft.

32 spline: (1973-77) This is the preferred shaft, as it is the strongest. These came behind Turbo 400 trannies.

Bolt Pattern:
Is an asymmetrical pattern unique to the 203. It is possible to disassemble this case and re-drill it for the 6 bolt circular pattern. An adapter is also available to mate this case to Jeep, Dodge or Ford 6 bolt circular applications: adapter PN AA50-0202

Ford NP203 Transfer Case
The Ford NP203 has a 31 spline female input. The bolt pattern is the Ford rotation of the 6 bolt circular bolt pattern.
Use with a Klune-V Extreme underdrive:
Use the Klune with the 31 spline output. These units will bolt up directly.
Dodge NP203 Transfer Case
The Dodge 203 has a 23 spline female input. Later model Dodge transfer cases use the 6 bolt circular bolt pattern. Early Dodge 203s use the same front bolt pattern as the early Chevy unit. It is an asymmetrical pattern unique to the 203. It is possible to disassemble this case and re-drill it for the 6 bolt circular pattern. An adapter is also available to mate this case to Jeep, Dodge or Ford 6 bolt circular applications: adapter PN AA50-0202

Transfer Case Specifications:
Low Range reduction ratio: 2.6 to 1
High Range: Direct 1:1
Chevy, Dodge and Ford all used variations of this transfer case. All were chain drive to the front output, with a light weight aluminum case. Most used a slip-yoke rear output. We are not aware of a Fixed yoke conversion for this case. While these units will hold up under moderately heavy off road use, they are not considered the preferred swap due to the chain drive and thin aluminum case.
Bolt Pattern:
6 bolt circular pattern. Note: This pattern is almost symmetrical, however it is not and will only bolt up one way. Chevy, Dodge and Ford all used the same bolt pattern, However with a different ROTATION of the pattern. Dodge and ford are close, and swaps might result in a useable Tcase droop angle, however Chevy units are about 90 degrees different and cannot be interchanged. Ford units have a driver side drop, While GM units are passenger side drop.

Chevy 208

Passenger side drop (front driveshaft). This Tcase has the GM rotation of the 6 bolt circular bolt pattern.

Input Spline: We have run into two different input spline configurations on these cases.

27 spline: The units supplied with a T350 or 700R4 automatic have a 27 spline female input shaft.

32 spline: This is the preferred shaft, as it is the strongest. These came behind Turbo 400 or SM465 transmissions.


Ford NP208 Transfer Case
The Ford NP208 has a 31 spline female input. The bolt pattern is the Ford rotation of the 6 bolt circular bolt pattern.
Use with a Klune-V Extreme underdrive:
Use the Klune with the 31 spline output. These units will bolt up directly.
Dodge NP208 Transfer Case
The Dodge 203 has a 23 spline female input. It uses the same front bolt pattern as the Chevy unit. The Klune is available with a 23 spline output shaft to match up to this application.

Transfer Case Specifications:
Low Range reduction ratio: 2.6 to 1
High Range: Direct 1:1
Chevy, Dodge and Ford all used variations of this transfer case. All were chain drive to the front output, with a light weight aluminum case. Most used a slip-yoke rear output. We are not aware of a Fixed yoke conversion for this case. While these units will hold up under moderately heavy off road use, they are not considered the preferred swap due to the chain drive and thin aluminum case.
Bolt Pattern:
6 bolt circular pattern. Note: This pattern is almost symmetrical, however it is not and will only bolt up one way. Chevy, Dodge and Ford all used the same bolt pattern, However with a different ROTATION of the pattern. Dodge and ford are close, and swaps might result in a useable Tcase droop angle, however Chevy units are about 90 degrees different and cannot be interchanged. Ford units have a driver side drop, While GM units are passenger side drop.

Chevy 208

Passenger side drop (front driveshaft). This Tcase has the GM rotation of the 6 bolt circular bolt pattern.

Input Spline: We have run into two different input spline configurations on these cases.

27 spline: The units supplied with a T350 or 700R4 automatic have a 27 spline female input shaft.

32 spline: This is the preferred shaft, as it is the strongest. These came behind Turbo 400 or SM465 transmissions.


Ford NP208 Transfer Case
The Ford NP208 has a 31 spline female input. The bolt pattern is the Ford rotation of the 6 bolt circular bolt pattern.
Use with a Klune-V Extreme underdrive:
Use the Klune with the 31 spline output. These units will bolt up directly.
Dodge NP208 Transfer Case
The Dodge 203 has a 23 spline female input. It uses the same front bolt pattern as the Chevy unit. The Klune is available with a 23 spline output shaft to match up to this application.

Hope this info helps. Are you going to spend more time on road then off? If the truck isn’t going to see major pounding and crawling. I would suggest moving to the 208. It is lighter and so much quieter and smoother on the road. My friends and I use the 205 for crawlers and the 208 for road babies. The 208 is reasonable, easy to find and a breeze to go through internally. Just my opinion. And what has worked well for me. oh yea, here is a link to some more info. http://chevy.off-road.com/chevy/arti....jsp?id=200867
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