During the three years of this cab design, subtle changes occurred as GM engineers learned better ways to construct this truck. The gas tank changes on the pickup body style was probably the most obvious and it was different each of the three years.
In 1936, the new mid year low cab pickup continued with the earlier practice of securing the tank under the bed and behind the rear axle. The gas add spout extended through a hole in the lower bed side behind the right rear fender. Thought it might seem like a good location, it was not. Considering the trucks stiff suspension the poor roads of the 1930′s, and how rough trucks were treated, this location resulted in tanks leaks and cracked fuel lines that were over 6 feet from the engine.
The answer to this problem came out in the 1937 trucks. The tank was moved to the protected area under the cab seat cushion. This solved prior problems but the improvement did not go far enough. The fuel add hole was in the top of the tank on the passenger side. To gain access to the threaded plug to add fuel, the right side of a new split bottom cushion was raised or removed. Rain or shine, the passenger would stand outside and wait for fueling so the seat cushion could be replaced. Of course, any accidental spills or splashing from the spout would give fumes within the cab till the evaporation was complete. What if you lit a cigarette out of habit? What about a small electrical short under the dash? Your imagination can tell you what probably happened a few times over the years.
The engineers seem to have got it together in mid 1938. They redesigned the 1937 tank and cab so that gasoline was added through a spout that now extended out the cab corner. The bottom seat cushion was then one piece, however, for several months two piece bottoms were still used on the assembly line until supplies were exhausted. Therefore, the late 1938 tank was used less than one year and is very rare today. The new designed 1939 body style continued with this type tank and cab design but the 39 tank will not interchange in the earlier cab.
1937 ( above)
Gas Spout Hole from Outside
Gas Spout Hole from Inside