Np205 input shaft swap

Np205 input shaft swap DEFAULT

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Join Date: Nov 2004

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Good info, but the 10-splined is the weakest input shaft among the four or so NP205 shafts used/available. If you mic the 10-splined at the depth of the splines and compare that to the 27 or 32 splined shafts, you'll note quite a difference. The course-cuts leave the 10-splined shaft much smaller at the cuts than the uncut portions or the fine-cuts in 27/32-splined shafts. The 10-splined shafts also wear more easily since the course cuts do not have as tight a slip fit as fine-cut 27/32-splined shafts. The trans to xfer case adapter 10-splined spud shafts also wear easier for the same reason. ORD has a good NP205 tech page.

72longbed, if strength for a powerful engine, agressive driving, ar large high-traction tires is not a concern, the 10-splined is fine. After all, they hold up for years behind manuals. But serious rockcrawlers, mudders, draggers etc often need greater xfer case strength. Good time for an upgrade though, since the case is out. Check for wear on the splines. That may drive your decision, some.

JC Whitney used to sell a NP205 overhaul manual that I bought once, but I can't find it despite both a home and online search.

'71 GMC K20 Suburban, '71 GMC K10 Suburban, '72 Chevy C10 CST Suburban, '72 Chevy K20 clunker pickup.

Last edited by 4x4Poet; 12-30-2004 at 04:51 AM.


Np205 input gear swap and 32 Spline front output swap

Here is some tech I thought I might share with you guys. Upon searching many hours on CK5/PBB myself and Maxxis85 decided to tear apart my big bearing round pattern 205 to swap in some goodies.
The reason we are swapping the long 32 Spline input gear to a short 32 Spline input gear is due to the Long 4.5" stickout on the back of the TH400 we are mating this tcase to. The long input on a 205 is made for a 2.5" stickout on a TH400 Hence us buying a short 32 spline input from a racetrack 205 which uses a 4.5" stickout tranny a 4"ish adapter and a short input. Thanks to Grumpyold Fart's thread on pirate we realized we could just swap input gears and be on our merry way. While doing that we decided to upgrade the stock GM 30 spline front output with a 32 spline front output and changed all 3 seals. Here is our attempt at a tech article, for your viewing pleasure.

first the twin stick shifters where removed



next the th400/6 bolt round adapter was removed


remove the rear output yoke using a 33mm socket



using a 14mm socket the rear bearing retainer is the next to come off



remove the rear output bearing


then the speedo gear



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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.


NP 205

NP 205

NP 205



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.

NP205 Idler Cover

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.

NP 205 Shifter Crossbar

  1. 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.

 NP205 10 spline input

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.

NP205 23 spline input

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

27 spline np205 input

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

31 Spline NP205 input

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

Divorced 32 Ford NP205 input

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.

Short 32 Spline GM NP 205 input

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.

Long 32 Spline GM NP 205 Input

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.

29 Spline Dodge NP 205 Input

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:

Slip Yoke NP 205 

Fixed output NP 205

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.

NP 205 cover

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

Syncro NP 205 Cover 

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. 

NP205 Measurements



International Full Size Jeep Association > Tire Kickin' > Off-Road FSJ Tech > NP205 swap : TH400 output shaft


View Full Version : NP205 swap : TH400 output shaft


05-22-2008, 02:22 AM

I've heard that there are (2) different 32spline transmission rear output shafts used in GMTH400-NP205 combos. A "short" version and a "long" version.

Of the figure 8 "racetrack" pattern NP205's and the round 6-bolt style GM 205's which one uses the shorter shaft and which one uses the longer?

FYI : I'm hunting down parts to swap in the round 6bolt style 205


05-22-2008, 02:25 AM

You will most likely need the longer one for the round pattern 205..

The difference between the 2 shafts is 1 inch...


05-22-2008, 02:33 AM

I assumed the longer one was for the figure 8 205 because the adapter looks thicker for that combo when compared to the smallish round pattern adapter.

I believe the short TH400 output shaft stick out is 2.5" and mates
to the long 32 splined NP205 input shaft stick out of 3.5".
The long NP205 input came in 85-91 1-ton GM trucks with the round patern
TH400 and the SM465 trannies.
It is important to make clear if you are refering to the TH400 output
or the NP205 input when using the "Long" or "short" reference so not to confuse the two.


05-24-2008, 02:03 AM

I believe the short TH400 output shaft stick out is 2.5" and mates
to the long 32 splined NP205 input shaft stick out of 3.5".
The long NP205 input came in 85-91 1-ton GM trucks with the round patern
TH400 and the SM465 trannies.
It is important to make clear if you are refering to the TH400 output
or the NP205 input when using the "Long" or "short" reference so not to confuse the two.
I referred to the TH400 "output shaft" in my original post. That is what I am searching for at the moment.

I get different answers on output shafts offered by GM with the TH400. Some guys are telling me that the only "short" 32-spline transmission output shaft GM made for the TH400 transmission was for the NP203 full-time case. Some guys are telling me the same "long" 32-spline 4wd TH400 output shaft can be used with the 32-spline input figure 8 NP205 AS WELL AS the round 6-bolt NP205 with the 32-spline input



05-24-2008, 07:39 AM

To bolt to a round pattern 205 adapter you'll need the long output. It sticks out of the 400 about 4.5".


05-24-2008, 03:15 PM

Hope so

I just bought the "long" one

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Swap shaft np205 input

Th400 to Ford NP205

I have a TH400 that I was told is out of an H1. It has a 2.5" stick out 32 spline output shaft. My front axle is a Superduty 35 spline D60 so I'm needing a driverside drop tcase.

I'm in the middle of build a cage/backhalf chassis, 2" rogue fab die, swapping from leafs to king coilovers, front and rear stretch, 6.0 swap, seats, harnesses, etc so my wallet has been used an abused these last three weeks collecting parts and buying tools.

I'm trying to keep this as budget friendly as I can

Considering last night was the first time I've ever even seen a picture of an Np205 I stayed up late and did some reading.

From what I gather is the Ford NP205 (married) is a 31 spline input shaft. Some GM np205 cases used a 32 spline input shaft along with a bigger bearing. The Ford 31 spline case
uses the same size bearing as the GM 32 spline input case.

GM also has 10 and 27 spline inputs but they are of no use to me.

The Ford also has 32 spline fixed yoke outputs vs GM 205s which can have either a fixed or slip yoke.

The Ford NP205 uses a 6 bolt pattern and GM is 8 bolt until they went to 6 bolt like on the Ford. The NP 208 which came mated to TH400 from the factory also uses the same 6 bolt pattern.

If I swap the GM 32 spline input into the Ford NP205 case I can use the factory TH400/NP208 adapter? Is there a more economical solution?

Is there anything I'm understanding wrong about these cases?

My build is running 37s, 5.38 gears in the axles, and I plan on stepping up to 42s asap.

With a stock 6.0, th400, is the 2:1 low going to be enough for 42s?

Should I stop being a bitch and pony up to build a 203/205 doubler or does that put me in used atlas territory?


Transfer case input shaft swap for the DIY trans build 241DLD

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