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Shop now for Parts and Manuals for 1973-1979 Chevy and GMC 4x4's with New Process NP203 Transfer Cases. Most items listed in stock for quick shipping.
General Motors used the optional New Process NP203 Full Time Transfer Case in 1973-1979 4x4 trucks. The NP203 is a heavy, chain drive transfer case that has a gear drive low range section mounted in front of a chain case. An open, inter-axle differential located in the rear output section splits power between the front and rear axle. For additional tractive effort, the differential can be locked out by shifting the floor mounted shift into either Hi-Loc or Low Loc.
Despite it's large size and considerable weight, the NP203 is not considered a strong or reliable transfer case. NP203 Transfer Cases built before October 1977 were particularly know for issues related to the 3/8 pitch x 2-1/2" wide chain jumping the sprockets. Later production cases use a 2"x 1/2 pitch chain that was more resistant to stretching.
The 1979 Oil Crisis had one good benifit in that it ended the use of the inefficient, gas-guzzling NP203 transfer case by all vehicle manufacturers. To increase the fuel economy of their 4x4s, many owners of vehicles equipped with the NP203 installed "Part Time Conversion Kits" in the transfer case and locking hubs in the front axle. These conversion kits basically eliminated the inter-axle differential. With a Part Time Kit installed and the lockouts in free, fuel economy did go up, however lubrication problems related to the conversion destroyed many converted transfer cases. Since the NP203 does not have an oil pump, it relies on the rotating chain to splash oil on the upper shaft components. When operating a converted NP203 in 4x2 mode with the hubs in Free, the chain does not rotate which leads to oil starvation and failure of the upper shaft components (Raising the oil level in modified NP203 Transfer Cases helped, but did not solve the lubrication issue) Relatively few vehicles equipped with the NP203 remained in service beyond the mid 1980's.
In an odd twist of fate, the front range section of the NP203 is now often used as a "doubler" gear box when mounted in front of stronger transfer cases. By itself, the range section which provides High (1:1), Low (1.96:1) and neutral positions is quite strong.
