oldbikeles wrote:Here (I hope) is the missing photo.
les.
That's a very similar looking gearbox to my Thwaites.
Here's what you must look at carefully:
1. The plate with the slot in between the selector rails - this wears oversize.
2. The gearbox lever rod end, this wears undersize, both on thickness and on the north/south dimension.
The result is that that it becomes possible to get the lever into neutral without pulling a selector rail into neutral and then this gives you the possibility to engage two gears at once. Neither of these two scenarios are helpful!
To fix it you need the MIG welder and angle grinder and carefully build it all up with weld and grind to restore the profiles. I've got mine nice and tight now very little slop - good for another 50 years or so!
Julian.