Hey all,
I finally took some time to examine the 1958 JC Whitney catalog page that Soggy contributed. Looks like there are only a total of 13 different PTO combinations at least from the 1928-1958 sample years. The sample set examined is only for single speed rear output PTO models. These all look to be the smaller series sizes as what Parker would now call a 100 series PTO. Some of the early straight cut gears in the non-syncro and Clark era can easily be differentiated from the later helical cut gear era further aiding in identification. The gear position of "engaged" and "disengaged" is much different on the big 3 manufacturers so that can aid in differentiating one variety of PTO from another. The gear position on Chevy (Muncie) seems to be unique from all of the other truck companies. Interesting to note that the Clark 5-speed transmission was used by REO, Dodge, Ford, GMC, and International and all of them used a similar PTO.
There is one part differentiation that I cant really understand pertaining to the Chevy trucks. One part number is listed for 1948-1950 Chevy trucks and a different part number for 1951-1958 Chevy trucks. I thought all of the SM420 transmissions were essentially the same from 1947-1967? What was the change at the 1950-1951 year?
Getting closer to making some sense of the myriad of part numbers on later PTO manufacturers, namely Chelsea. Perhaps if we could assemble a list of other PTO part numbers found on "trucks in the wild", a trend may appear. If you happen to be under your dump bed Chevy, please take note of the PTO brand and part number and pass it along.
Paul
