According to the parts manuals there are no differences in the gearbox over the year. However this seems wrong. We have found out that there are different shells but with the same casting and part number. The parts are however not interchangeable between these different models. 

Due to the gearbox serial number we have concluded that there are early 1937, 1937-1945, 1946 (speedometer gears on the drive size) and >194x (internal speedometer gears)

Early 1937

The early 1937 ones are easily identified due to the fact that they are missing a screw on the outer lid. The later models come with an extra screw left of the kickstarter.

1937 – 1945

1946

These have an external speedo drive which bolted to the gearbox housing. The principle is the same as for the ones in the front wheel but them attached to the gearbox. The drive gear is actually a double gear, one for the rear chain and one for this speedometer drive.

Unfortunately I’m not able to find any pictures showing this configuration

Post war

These can be identified by the speedometer part which sits at the front bottom

Camplate

The material used inside the gearbox seem to also differ. It really shows the camplate, but the gears are also of the different color and possibly a different material. There are even cast iron camplates, which I have never seem in the war time gearboxes and are possible post war

Casting number

Below pictures of the casting number showing the same on both the 1937 and 1938-1945 model. I one tried to put mix casing parts between the 2 models, but they wouldn’t fit.

Gear ratio’s

The gearboxes seems to come in two different variants, the normal and the wide ratio.

Wide ratio gearboxes are usually stamped on the top with WR, but not always. While driving one will notice that it has a very short 1st and 2nd and a long 3rd and 4th compared to the normal ones. The WR gearboxes seems to be for the military where the snale speed of the first gear was needed in the field.