New Process 205

The 205 is a part time 4WD case, meaning when it's in 2WD the front driveshaft will not receive power.  It has 4 stock shift positions, 2WD Hi, 4WD Hi, Neutral, and 4WD Lo.
 

The New Process 205 was used extensively in GM trucks, they were available in their full truck lineup from '69-'80 and then only in K30's from '81-'91.  All GM 205's are married versions and all are right hand drop.

Ford used NP205's almost exclusively from '74-'79, they are a mixture of married and divorced versions, all are left hand drop.

Dodge used divorced NP205's from '69-'74 in their entire truck line, then used married NP205's only in the W250 and W350 trucks from '80-'93.

The NP205 is identified by several features:

1. The transfer case is one piece of cast iron.  There is a short bearing retainer/output housing at the tail of the case, and aluminum bearing retainers/seal retainers at the front and rear outputs but the working parts are all in a single iron housing.
 
2. There is a small idler shaft cover on the back of the 205 with 3 small bolts holding it on.  This is somewhat unique among transfer cases.

3. The overall length of the NP205 (in fixed output yoke versions) is about 12-13" from the front of the case to the center of the output yoke.

4. The shifter is a very simple lever operating a crossbar between the two shift rails that plunge in and out the front of the case.

5. The ID tag is found above the front driveshaft output, and will list model, manufacture date and gear ratio.

NP205's came with a variety of input gears depending on application:

10 spline male: Common behind SM465 transmissions from the late 60’s through 1984. 
~1.10" minor diameter.

23 spline male: Came in all 1980 4WD Dodge trucks, most 81-93 W250’s and all 81-93 W350’s except those with Cummins engine and Getrag 5 speed manual (see 29 spline). 
~1.10" minor diameter.

27 spline male: Common behind TH350 transmissions from the late 60’s through 1980. 
~1.10" minor diameter.

31 spline female: Common in Ford trucks through the 70’s
~1.24" minor diameter.

Divorced 32 spline male: Ford (73-77.5 F250’s only), Dodge (69-74) and IH pickups.
~1.27" minor diameter.

32 spline female, short: Found in 76-84 Chevy K30’s with TH400.  Sticks out 1-7/16” out from the front of the case once installed
~1.27" minor diameter.

32 spline female, long: Found in 85-91 Chevy K30’s regardless of transmission, these use the GM round pattern case.  Also found in uncommon CUCV military pickups with on-board generator in figure 8 cases.  Sticks out 3-11/16”out from the front of the case once installed.
~1.27" minor diameter.

29 spline male: Rare, only found in 89-93 Dodge trucks with the Cummins diesel and the Getrag 5 speed manual.
~1.38" minor diameter.

Output Shafts

Ford and Dodge NP205's use 32 spline fixed outputs front and rear, always.

GM rear output shafts were fixed style from '69-'79.  In '80, all GM trucks got 205's with a slip yoke rear output.  From '81-'91, 205's only came in K30's, and single cab trucks got a slip yoke rear output, crew cabs got a fixed rear output.  The fixed yoke and slip yoke rear outputs are interchangeable.

Pictured below is a Slip yoke rear output and a fixed yoke:

GM front outputs varied as well.  The early ~'77 and older cases got 10 spline front outputs with a 1310 CV yoke while ~'78 and newer GM 205's got 30 spline front outputs with a flat flange.  The bigger Ford/Dodge 32 spline front output is a direct swap for either.
 

Synchronized NP205

In the early 80's GM introduced automatic locking hubs, these required a special synchronizer on the front output to spin the front driveshaft and make the front hubs lock when you pull back on the 4WD shifter.  The 1/2 and 3/4 ton trucks were addressed easily with the introduction of the 208 that was synchronized from day 1, the 205 had to be retrofitted for K30's that got this rare (on K30's anyway) option.  Only K30's with auto hubs got synchro 205's, K30's with manual or full time hubs got normal 205's.

 You can tell a synchro 205 from a non-synchro 205 externally quite easily by looking at the back of the front output.  See pictures below:

Normal 205 cover, if the bearing is removed there is a hole in the center of it.

Pictured below is a synchro 205 cover, the aluminum casting covers up the bearing, there is also an oiling groove that is unique.

The synchro 205 is generally undesirable because parts are tougher to come by and, because everything on the front output side is special (the gears, shift fork, even the shift rail!), you have to replace a bunch of parts to put a 32 spline front output in it and modified shift rails (for front wheel drive only) aren't available for the synchro version.
 

Speedometer Parts

GM 205 pencil gears have varying tooth counts, those are how the speedometer is adjusted.  There is a letter stamped on the side dictating how many teeth the gear has:

The speedometer gear on the output shaft can't be substituted with another, they will physically interchange but the teeth are different heights and the pencil gear won't mesh with the wrong output shaft gear.  Output shaft speedometer gear tooth counts below:

Early GM metal speedometer gear - 5 teeth
Red/Yellow GM/Dodge speedometer gear - 6 teeth
Clear Ford speedometer gear - 7 teeth

Below are some measurements of the NP205, they should be used for approximation only.