1939-1948 2nd Gears Interchangeable?
 

Sorting through some parts and noticed two different mainshafts used, 81A-7061 for 1939-1942 and 51A-7061 for 1946-1948. Also the second gears were changed at the same time, 81A-7102 for 1939-1942 and 51A-7102 for 1946-1948.
The 81A design incorporates a spacer held in place with a pin in the mainshaft. The 51A design extends the main shaft and eliminates the spacer.
The 81A 2nd gear has a wide thrust surface to fit the spacer. The 51A 2nd gear has a narrow thrust surface that rides directly on the main shaft.
My question is, "Can the different 2nd gears be swapped or interchanged and function correctly between the two different mainshaft designs?"

Re: 1939-1948 2nd Gears Interchangeable?
 

Mac VanPelt could give you a better answer but I think it really depends on which main shaft you have and whether your cluster is a 24 tooth at the 2nd gear mesh or not. The earlier main shaft has to use the correct thrust washers and the pin hole with the 2nd gear corresponding. I think they are enterchangable if the pin hole & thrust washers aren't a factor.

Re: 1939-1948 2nd Gears Interchangeable?
 

I don't believe the interchange will work well between the 2 different shafts and gears. The 81A gear has an oil slot on it that will tend to bind with the helical spline on the 51A shaft because there isn't a thrust washer used. The 51A gear could be used with the 81A shaft if an oil slot is cut into the gear, not the best though would most likely work.
All in all I think a person would be wise to keep the 2 series of parts together and not mix them.

Paul J.