I recently bought a NOS girder fork M20 front wheel which was complete apart from the brake plate. Included in the purchase was a NOS speedo drive, which was fitted..
I am pretty sure this was not a WD wheel as it was finished in black and I could find no trace of olive drab.
So, possibly an early post war wheel (girders were fitted until the start of the 1948 season).
However, the speedo drive is of a different pattern to the 'normal' WD type...the overall width of the drive body is wider than normal (.648" for the WD type as opposed to .787" for the 'odd' one). The extra width is the result of a different (wider)pattern seal being fitted around the main drive gear. General style of the body is the same as WD types. Also the markings on the case differ.
The WD type is marked on its outer face 'Brit. Pat.529397'..this one is also marked on the outer face but says..'Smiths Motor Accessories Ltd. England Brit. Pat. 529397 Gear Ratio 2-1'.
The hole for the wheel spindle is the correct size, direction of rotation is correct and the unit fits correctly onto the wheel hub.
Does anyone have knowledge of, or information on this drive unit?....Ian
email (option): ian@wright52.plus.com
I had one on my 1939 M20 when I got it.
The reason the speedo didnt work on mine wasitdidnt have any guts in the drive.
So I ended up swapping it.
Thanks Sam..as I suspected a later replacement. I guess they had to meet the demand from the services until the M20 went out of service in the late 60s...Ian
email (option): ian@wright52.plus.com