NP205 Tech INFO
We've created this section to help our customers learn the ins and outs of the NP205 transfer case. Please keep in mind that this information is presented to be accurate to the best of our knowledge. Don't treat it as absolute truth, the factory did some strange things from time to time.
click here for: NP203/NP205 transfer case ID guide
Input Gear configurations:
Here are the 4 available GM input gear configurations. From left to right: 32 spline "short", 32 spline "long", 10 spline with a worn drivesleeve, 27 spline with a new drivesleeve.
GM used 4 different input gears in the 205. The first is the 10 spline male "coarse" input which came with the SM465 manual transmission. This sticks out from the case about 2". The factory used a fully splined "drive sleeve" to mate the male transmission output shaft to the male t-case input gear. This input gear routinely wears, most commonly in the drivesleeve, but often on the input splines directly. Note the pointed profile on the teeth in the above picture. This drivesleeve has lost about half of its tooth to wear and has a good bit of slop on the shaft. This is the most common 205 setup there is.
The next input is the 27 spline male "fine" input which came with the TH350 transmission. It also used a female drive sleeve between the transmission output shaft and the male t-case input. This shaft sticks out of the case by about 2" also. These gears wear well, but have been know to strip splines out of the drive sleeve, but usually after a long and happy life. The proper shaft stickout from the back of the TH350 case for this 205 configuration is about 7/8". This is the same as the stickout for use with a NP203 transfer case also.
Next up is the biggest and best input, the short 32 spline female. This came with TH400 transmissions and is as strong and as durable as anything can be on a truck. It wears very well and does not use a drive sleeve, so there is one less splined connection to create "slop" (backlash) in the drivetrain. This shaft sticks out of the 205 case by about 1 1/4" and the male transmission shaft plugs directly into it. The proper shaft stickout from the back of the TH400 for this type of 205 input gear is about 4 1/2". This gear configuration is the one necessary to run our GEN2 Doubler kit.
Last is the "long" 32 spline female input gear. This is far less common than the "short" 32 spline input outlined above, but is as strong and durable. This gear will stick out of the 205 case by about 3 1/2". This was used behind later model SM465 trannies and later TH400 trannies, from about '85 to '91 in straight axle 1-ton trucks. Proper shaft stickout from the TH400 is 2 1/2", and the proper SM465 output is the later model 32 spline output shaft with the round bolt pattern adapter housing. This gear will not work with the GEN2 Doubler, but is easily replaced with the short 32 spline input gear.
