47-59 Napco 4x4

[MJN]

Originally Posted by sack54

I do believe Napco was not used in 1960 as GM built 4x4 completely
My 1956 GMC was line built / Chevys were line built starting 1957

This is correct, GMC's were factory installed beginning in 1956 and Chevy followed in 1957. Now, not all Napco's during these years were factory and you could still purchase an upfit kit from a dealer to retrofit your 2wd truck to a Napco. GM stopped installing Napco's on 1/2 and 3/4 ton trucks in 1960 when they began using Dana front axles and Rockwell T-221 transfer cases, 1 tons continued to be upfitted through 1977 as there were no factory 1ton 4x4's until then. I'm not familiar enough with these years if the factory continued installing the kits or if they were only available as a dealer upfit. Larger trucks were also upfitted with Napco, Coleman and Marmon-Harrington kits beyond 1960.

Originally Posted by Louisvillekytruck

Does anybody have pics of the rearend and frontend what did napco use

The rear axle was the standard factory installed axle since the Napco setup only added the transfer case, driveshafts, front axle, rear lift blocks and a few other odds and ends. The 1/2 tons used HO-33 Eaton or Spicer 45, 3/4 tons used HO52 rear axles and 1 ton used HO 72 Eaton axles. Only three gear ratios were available with the Napco kit as well; 3.90:1 for 1/2 ton, 4.57 for 3/4 ton and 5.14 for 1 tons.
Here is a picture of the front axle from my '56 3600 pickup- still in process of being restored. My truck was an upfit by a dealer and is a bit of an odd ball being a drivers side differential with a Timken/Rockwell T32 transfer case. Typically '55 and newer had passenger side differentials as well as Spicer 23 transfer cases. The front axles were based on the GM Eaton rear axle, same third member and differential cover as the rear axle.