Transfer case info

[kipps]

I was messing around with the 'Vehicle Information Kits' on the GM heritage website, and found some interesting info about transfer cases.

In 1973, the np205 was the only option for the k10 and k20 trucks.

From 1974 and 1975, the new np203 was used on the v8 trucks, and the np205 continued to be used on the i6 trucks. For 1974, the np205 could have been special ordered for the v8 trucks.

From 1976 through 1979, the np203 was used on the automatic-trans trucks, regardless of engine type. The np205 was used on the manual-trans trucks, regardless of engine type. This applied to the k30 as well, when it was introduced in 1977.

I suspect the reasoning here was that GM considered the np203 and np205 to be equally strong. They were favoring the convenient full-time 4wd for the automatic trucks, and figured if you were willing to shift gears, then you would also be willing to lock in your own hubs.

In 1980, the np203 was no longer an option, and the np205 was the only transfer case available for this one year.

Up until this point, the np203 and np205 both had the classic figure-eight bolt pattern, and they had differing spline counts depending what transmission was bolted to the front. The th350 had 27 splines, the th400 had 32 splines, and the sm465 had 10 splines.

I don't know what the spline count was of the heavier-duty and lighter-duty three-speed column-shift transmissions. I suspect they had the same 10-spline count as the sm465, but that's a guess only.

From 1981 through 1984, the k30 continued to use the np205 only. If the np205 was bolted to a sm465, it used the figure-eight pattern and 10-spline shaft that it did before. If the np205 was bolted to a th400, it used the figure-eight pattern and 32-spline shaft that it did before. The np205 was no longer being bolted to any of the lighter 27-spline automatics.

From 1981 through 1984, the k10 and k20 used the new np208 exclusively. This transfer case was only available in round pattern, and 27 & 32 spline input shafts. There was no 10-spline option for the np208. Because of this, the sm465 and th400 switched to the round-pattern 32-spline shaft when bolted to this np208.

The three-speed th350 was phased out and replaced by the four-speed 700r4 between 1982 and 1984. These two transmissions were the only ones that used the 27-spline shaft. These were used in the k10 trucks, and the light-duty k20 trucks.

In 1985, GM finally simplified the lineup. They dropped the 10-spline and figure-eight pattern altogether on the np205. Everything was now round-pattern, and was only 27-spline or 32-spline.

In approximately 1988 or 1989, the np208 was phased out, and replaced by the np241. The two transfer cases are identical in fitment; the np241 is significantly updated over the np208.

The np205 was last used in the 1991 crew-cab trucks.

The military m1008 k30 trucks were model years 1984 through 1987. These were different from the civilian k30 trucks, in that they used the np208/th400 combo exclusively. These did not use the np205. Edit: the m1028 k30 trucks did use the np205/th400 combo.

Any corrections to this list are welcome. Also, if anyone can shed light on how GM chose between the th350 and the th400 during the 1970's, that would be helpful. The GM literature I was reading didn't make any distinction between the two.

[57taskforce]

Nice write up, I’m fairly confident the round 205 is only ‘85+ (91) and all of them came in the K30, all were 32 spline, and only came behind the th400, SM465, and in the ‘91 crew cab The 4L80E. 4 400/round 205 combos stashed as well as 1 465/round 205. (Only real addition to what you posted was the 4L80 in ‘91)

[kipps]

Someone else on a different group said the reason the full-time np203 was only offered behind automatics for several years had to do with the annoying jerkiness when turning. The automatic transmission helped damper some of that jerkiness.

[Getter-Done]

Great Info.

I am currently in the process of building a 208 for my 84 Chevy.

There are several U tube videos.

And documented Stuff.

I was kind of thinking of posting pictures of the rebuild.

This 208 is So simple thou.

I plan to have my Nephew help

So I can expand this stuff and spread the Gearhead Era to the Youngens.

[Willowrun]

Great post and fun to read as the "gear to gear" strength has been talked about since the NP205 came out, and I've grown to appreciate the big chain drive NP203 especially with a part time kit.

The depressing thing about this post is it reminds me of where all of these NP (New Process) transfer cases were manufactured. They were all made in a giant plant in Syracuse, NY that I visited in the early 2000's while it was running at full steam. I'm in manufacturing and visit a lot of plants so as a 4x4 enthusiast it was really cool to see where the transfer cases I knew so much about had been made.

Fast forward ten years and a customer of ours in Mexico was receiving all of the machines/equipment/tooling from Syracuse to start making the transfer cases there. Crazy to see half high dunnage chocked with stuff from that big plant that was now closing. No politics please...just sad to see an old plant close and I've seen a few.

Regarding what manufacturers decide to put in what is it oftentimes depending on the production capacity and parts availability of the plants providing the product. The older tech transfer tech while very fast and efficient when running, were expensive, high maintenance, and if they do go down they shut down the entire production of the product so to have other options to fulfill demand is a good thing and in many cases what drives the balance between different options on a vehicle. Every day is a fire fight in manufacturing to keep the lines running but today's CNC production lines allow for at least partial production if a machine breaks as there is redundancy.

[MJN]

Originally Posted by kipps

Someone else on a different group said the reason the full-time np203 was only offered behind automatics for several years had to do with the annoying jerkiness when turning. The automatic transmission helped damper some of that jerkiness.

I also saw that post and can attest to the jerkiness while turning. I would also imagine production take-rate had a part to play along with the customer feedback. My '74 K20 was a 465/203 combo from the factory but I swapped it to a 205 to make it more drivable and less wear/tear on all the driveline parts. I kept the transfer case, adapter and drive flanges if I ever decided to return it back to as-built. I also would say the NP205 wasn't a 'special' order item, rather just a production option when the NP203 was standard equipment based on base model code. Same treatment to getting any other RPO (mirrors, trim package, etc) when buying your truck.

[MJN]

One other comment- I would say based on the SM465/NP203 adapter the NP203 was not a figure 8 pattern like the NP205 was. As you can see the side with blue RTV is the transfer case side of the adapter- the oily side is the SM465 side. Also, another nuance with the NP203- it used a 10 spline female input and coupled directly to the SM465 and did not use a splined coupling like the NP205 did.

[Accelo]

The annoying jerkiness when turning was caused by the Cardan joints (U-joints/universal joints) at the outer end of the front axles. This was the reason all modern trucks use CV joints.

[HOTFUN]

Back when these new process 203 chain drive came out and versus the 205 gear system GM was boasting their quietness and effortless shifting with the full time system. Didnt take long to figure the fuel mileage difference and the additional wear on full time turning components to have everyone putting lockouts on their full time GM trucks.
Trucks were getting more and more car like in the squarebody design years. Streamlined cabs no more windshield gutters to cut wind noise and power window /lock options and full interior lining options by the 1977 models.

[wazzabie]

There also was an added support support brace from the tcase to the auto tranny. This was around 1978. Prior to 1978 a support brace that went from the tcase to the frame. I'm not sure on the exact years for these changes. Also not all trucks had this or in later years they were removed by the owner.

Early np203 housings (1974-?) are one piece compared to the later np203 housing. This might only have been a two year run.

[GM72K10]

Not to be too picky but the CUCV M1028 DID use the NP208/TH400 combo. Only M1028a1, M1028a2 and M1031 model CUCVs had the NP205s.

[kipps]

Originally Posted by wazzabie

There also was an added support support brace from the tcase to the auto tranny. This was around 1978. Prior to 1978 a support brace that went from the tcase to the frame. I'm not sure on the exact years for these changes. Also not all trucks had this or in later years they were removed by the owner.

Whoever thought that bracing the t-case to the frame was a good idea? It seems like that's a recipe for broken bellhousings and transmission rear housings, if the t-case can't budge at all, but the engine can move in its mounts.

My 1987 did not have a t-case to bell brace when I got it. I bought a brace for a th400/np208 truck that was the correct length for my sm465/np208 combo, and it still fits on my nv4500/np241 setup.