This LRO reader emailed LRO.firstname.lastname@example.org looking for help with a sticky Series III gearbox .
My Series III jumps out of third and fourth gears. I’ve stretched the detent springs, tightened the main shaft nut, and checked the forks and gears for wear. Putting it together, I can’t select any gears when the interlocking plungers are in place; without them I can select gears. What is it that I’ve done wrong?
Nathan Young, Suffolk
Extending your detent springs won’t stop the gearbox jumping out of gear. It’s more likely to be worn gear teeth on the centre of the third/fourth gear synchromesh hub unit, or you may have lost its three butterfly springs.
The interlocking plungers won’t stop your selector shafts moving as long as they’re free to move in their grooves. But if you start without all three shafts lined up exactly, the two that are in line will be locked by the third one that has already moved. I’ve found having the top cover too tight can lock the selector shafts. Try loosening it a little.
This workshop advice appeared in the July 2015 issue of LRO. Back issues are available to download on digital devices here.