Another Sample Article from the July - August 2013 MASCOT -
From the President’s Patois - by John Horne
Which Gearbox? I have been asked to confirm that this gearbox is from a 1934 Nine Sports. Well, first of all it has the clutch pedal pivot on the case, so it is between 1933 and 1935. To find out which year, it is necessary to count the number of teeth on its output shaft gears.
Removing the top cover revealed 20 teeth on the Input (Layshaft drive) gear and 26, 31 and 39 resp on the Output shaft. Reference to my Table of Gear Teeth Numbers shows that this is a 1935 standard ratio box. The Table is reproduced below. You will see there are four types of gearbox cases, three types of gears, and two types of gear ratio. See the Notes below for details of the differences. There are also two types of bell housing.
Cases Type 1 & 2 carry the clutch pedal mounting, and the height from the centre line of the input and main shafts to the lid is about 3/16” less than on Types 3 & 4.
Case Type 1 was used for the 1933 to 1934 models in conjunction with Type A Gears. With the exception of the Close Ratio (C/R) 3rd Speed Mainshaft gears, Type A Gears have fewer teeth with thicker roots.
Note: Type 1 Cases and Type A Gears are not interchangeable with any of the others.
Case Type 2 was used for the 1935 models with Type B Gears.
Case Type 3 does not carry the clutch pedal mounting. It was used for the 1936 &1937 models, with Type B Gears. These models also had larger diameter clutch splines as on the 1.5 Ltr Le Mans.
Case Type 4 carries the clutch pedal mounting. It was used for the 1934 & 1935 9 hp Le Mans models, and, with Type C/R Gears, (Close Ratio), as an option for the four seater. Type C/R gears are not interchangeable with any of the others because of a different (straighter) helical cut.
All types of gear box case fit the two types of bell housing.
The different types of speedo drive gears must be used as matched pairs.
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