Gearbox Actuator Arm

image of Gear Actuator arm with missing section blanked out
image of full Gear Actuator arm

The arm in the picture is an actuator arm off a 1930’s MG fitted with a pre-selector gearbox. These gearboxes are semi automatic, that is they only change gear when the clutch pedal is pressed. This is attractive for racing enabling the driver to ‘set up’ the gear box ready to accelerate out of a say a corner. A similar approach is used on racing cars to this day albeit computer controlled.

When this actuator arm was given to me to repair it was missing the section blanked out in the first photograph.

There were no drawings or pictures of what arm would have looked like. By measuring mating components and measuring the what the arm length had to be from  the remaining mechanism it was possible to infer the dimensions of the arm. Using pictures of other ‘arms’ on the car it was possible to work out what the arm should look like. I set to work pre-machining a steel piece slightly larger than the measurements of the components is needed to fit. After setting the face of the large hole flat it was possible to see where the new arm should be looking at the broken face what was left of the old arm. It was then possible to set it up to weld on the new piece. After final machining to size and some careful hand filing the result is on the next picture. Ready for action on a 70 year old gearbox.