GM TRANSMISSION AND TRANSFER CASE INFORMATION:
The early GMs 1968-70 used a Dana 20 & Rockwell style transfer case and no adapters are available for these vehicles.
In 1971, New Process introduced a model NP203 (chain-driven), and NP205 (gear-driven) transfer case. Both of these transfer cases used various input splines. As a general rule, all of the transfer cases that couple to a TH350 automatic are normally a 27 spline input; when coupled to a manual transmission a 10 spline input; and when coupled to a TH400 a 32 spline input.
The NP203 was used from 1971 to 1978. This transfer case was mated to the TH350, TH400, and SM465 transmission.
The NP205 was used from 1971 to 1991. The 1971-79 NP205 was only found mated to the TH350 and the SM465 transmission. For 1-ton vehicles between 1979 to 1984/85, GM used a TH400 and the SM465. The TH400 was equipped with a female 32 spline input, while the SM465 retained the male 10 spline input. These model transfer cases had a figure-eight front bolt pattern. In 1985 to 1991 vehicles, GM started using a different version of the NP205. The input spline for both the TH400 and the SM465 transmissions was a female 32 spline, and the front bolt pattern changed to circular bolt pattern.
In 1981, GM introduced the NP208 chain-driven transfer case. The NP208 also has a circular bolt pattern, and had either a 27 or 32 spline input. In 1988, GM next introduced the NP241 chain-driven transfer case. This transfer case, as far as bolt patterns and splines are concerned, is identical to the NP208.
The NP205 is sometimes hard to identify. The data plate for this transfer case is located on the upper front of the case; but many times this information has been worn off, and subsequently a NP205 gets confused with a NP203 transfer case. The easiest way to identify the NP205 is by the rear 3 bolt cover on the idler shaft.
Once you know that you have a NP205 transfer case, the next thing is to identify the make (GM, Dodge or Ford). The casting numbers on these cases are of no help. The Ford transfer case is the easy one to identify since it is a left hand drop (front driveshaft on the driver's side). The Dodge and GM NP205s are a bit more difficult. The cases are identical, both having the figure-eight bolt pattern. Counting the front input gears are the easiest way to distinguish between the two. GM transfer cases use either a male 27 spline (TH350), a male 10 spline (SM465), or a female 32 spline (TH400) input gear. The Dodge NP205 was either a male 23 or male 29 spline input gear. The GM female 32 spline shafts were offered in two stick out lengths: 1979 to 1984/85 had a short stick out, while the 1985-91 had a long stick out. The 32 spline stick out is important to know when adapting to a different transmission.
The NP205 input gears, no matter what vintage or model, are always the same internally. This allows you to swap the input shaft between the various model transfer cases. One difference that must be taken into consideration is the front input shaft bearing. The male 10 & 27 spline GM & 23 spline Dodge transfer cases used a smaller bearing than the female 32 spline GM 29 spline Dodge & 31 spline Ford transfer case. The last thing that should be noted is the bolt pattern change that occurred on the case of the GM NP205 transfer case. In 1985, the case was changed from a figure-eight bolt pattern to a circular-six bolt pattern. This circular bolt pattern is identical to that of the NP208/241. The stock adapter housings that GM used are similar; however, the NP205 stock adapter housings have a notch in them for transfer case shifter linkage clearance and the housing is 1.625" longer.
NP205 originally coupled to a TH350: This transfer case, used in vehicles between 1971-79, has a male 27 spline input. The bolt pattern is a figure-eight configuration.
NP205 originally coupled to a SM465: Used in vehicles 1971 to 1984, this transfer case has a male 10 spline input. The bolt pattern is a figure-eight configuration.
NP205 originally coupled to a TH400: Used in 1979 to 1984 vehicles, this transfer case has a short stick out of 2", and a female 32 spline input. The bolt pattern is a figure-eight configuration. This transfer case uses a larger front bearing than the 10 and 27 spline transfer cases.
NP205 originally coupled to a SM465 or TH400: Found in 1985-91 vehicles, this transfer case has a long stick out of approximately 3.50", and a female 32 spline input. The bolt pattern is a circular-six configuration. This transfer case uses a larger front bearing than the 10 and 27 spline transfer cases. When using this transfer case, caution should be used with regards to the length of spline engagement. Transfer cases with this long stick out may require a spacer adapter 50-6910 or modifications to the transmission output shaft for proper spline engagement without pre-loading the transmission or transfer case bearings. Note: 1985 TH400 could have a short 2" input stickout with the circular 6 bolt pattern.
NP205 Stock Couplers (Power Sleeves): As the ongoing aging process of GM NP205 transfer cases continues, so does the good availability of replacement part from the dealerships. The most recent GM components that started to become hard-to-find items are the power sleeves. We now offer both the stock GM 27 spline and the stock 10 spline. The 27 spline was offered in two designs: one that used a bearing support in the adapter housing, and one that floated on the transmission and transfer case splines. We only offer the later one which is centered by the splines. Our 52-9503 fits the 4WD TH350 transmission to the 27 spline NP205 transfer case, and 52-9504 fits the 10 spline SM465 transmission to the 10 spline NP205 transfer case.
Along with the stock replacement power sleeves we offer custom ones. These are couplers that we have designed for coupling the different transfer case inputs to the opposite transmission. 52-9502 - Fits the GM SM465 10 spline to the GM NP205 27 spline, you will also need a new seal 716728. 50-5304 - Fits the GM TH350 27 spline to the GM NP205 10 spline.
NP205 Stock Replacement Adapters: The same goes with the adapter housings as does the power sleeves. We offer a stock TH350 to NP205 adapter 50-5302. We offer SM465 to NP205 10 spline pattern 50-4708 and a TH400 to the early pattern NP205 51-3202.
NP205 addition notes: Slip yoke and fixed rear outputs used depending on wheel base of the vehicle.
Front outputs: 71-77 10 spline front output shafts and normally used 1310 or 1310C.V. yokes. 77-91 30 spline front output and normally had a flange front yoke Saginaw U-joints.
All Chevy NP205's were married units. All Chevy NP205's 1971-1984 have fig 8 bolt pattern
TH350 71-79 transmission used a male 27 spline input and small input bearing with a coupler sleeve figure 8 bolt patterns. SM465 71-84 used a 10 spline male input and small input bearing with a coupler sleeve figure 8 bolt patterns. TH400 79-84 female 32 spline input large input bearing figure 8 bolt pattern no coupler used and female input sticks out 2" from the front of the case. 1985-1991 Only used in 1 ton dually or 3+3 cab trucks (unless special order) Circle 6 bolt pattern 32 spline female inputs with the large input bearing. This was used behind TH400 and SM465. In 1991 production vehicles and special built Chevy railroad trucks in 1992 were offered with a NP205/4L80E. These cases have a 40 pulse VSS tail housing and special 4L80E adapter casting. 2 different length inputs used (short input 2" known to be used in 1985 W/TH400 and most were long 3.5" stick out from the front of the transfer case. All Circle 6-bolt SM465 are the long input)
The NP205 is a popular transfer case adapting it to some of the newer GM transmission options, We offer a full adapter line of adapters for the 4L80E, 6L80E, 6L90E & the NV4500. Search any of these transmissions on the home page for a complete list of adapter kits we offer.