Back to the Technical Articles main page
Back to Transmission section
Replacing 4-speed gearbox selector spring in situ
Author: Dave Mann
After 55 years of driving Sevens I finally experienced failure of the first/second selector ball spring on a 4-speed gearbox. When you engage first gear the weight of a standard gear lever causes it to fall out of first and into second, so you have to hold it in first till you get the clutch engaged then the driving load keeps it there. I didn't feel up to dragging the engine and gearbox out in the freezing cold so thought about it and realised I might be able to replace the spring with the gearbox in place. This method only works for the first/second and reverse selector springs on a 4-speed gearbox attached to a 3-speed engine & clutch assembly.
- Remove floor plates over flywheel and fabric coupling.
- Remove starter and its mounting case.
- Make sure there is nothing likely to fall into the gearbox and remove gearbox top.
- Screw the selector bar out and very carefully slide it forwards till it touches the clutch centre plate, if it hits a toggle arm turn the engine a bit.
- Very gently slide the selector forward and put a suitable red cap in its end to keep the ball and broken spring from falling into the gearbox.
- I made an electromagnet by winding numerous turns of enamelled copper wire round a 1/4" rod and with a 21 watt bulb in series connected to the battery to extract the ball. A bent piece of wire was used to hook out all of the broken spring coils.
- When you are satisfied all the bits of broken spring have been removed fit your new spring and using the electromagnet refit the ball switching off the power when it is in place.
- Remove red cap gently and pass a 5/16" rod through the threaded hole in gearbox and into the selector.
- Very gently slide the selector and its bar back into place making sure the ball stays in place.
- Screw the selector bar back into its correct position and lock it with its lock nut.
- Refit gearbox cover and check operation of gearlever are all gears selectable.
- Refit the starter and its mounting.
- Refit floor plates over flywheel and fabric coupling.
To do the operation on an engine with a 4-speed clutch it is necessary to split the engine and gearbox by about 1" in order to move the selector far enough forward because the bore of a 4-speed clutch cover is smaller than the 3-speed.
Download the article