Originally Posted by buoymaker
I would guess the 1939 1/2 ton panel truck uses the same master cylinder as a 1939 1/2 ton truck.
The Master Parts List says 1 inch diameter master cylinder 1938-1946 for a 1/2 ton.
Cast number 5450256. Part number 5454575. Is this what you have now?

The Cast number 5450256 is good but the Part number is 5454576

Chevs of the 40'S has a new one for 178.50.

Chevs of the 40'S