With the gearbox on the bench, it’s a quick job to remove the bell housing and expose the ends of the main shaft and lay shaft.

The synchromesh is on the end of the main shaft so it will be easy to diagnose the problem.

First of all the clutch withdrawal mechanism needs to be removed.

The workshop manual comes in handy… once again
The clutch release mechanism. When you push the pedal, the metal disc in the middle presses against the pressure plate and the clutch plate is released.
Release mechanism removed. I’ll clean the bits of gasket and sealant before refitting.
Next the handbrake drum is “locked on, hard”. With the gearbox in gear, the castleated nut on the layshaft can be removed.
Split pin is removed from the lay shaft but. A new replacement one will be ordered.
Gearbox selector moved into first gear position
Castleated nut and thrust washer are removed
Thrust washer seems rather worn… I’ll put that on the parts order list too.
Next up… removal of the bell housing.
There are 4 fixings holding the bell housing to the main box.
Tight fitting bolts are drifted out
Fixings removed… the top left fixing is a stud screwed into the main gearbox.
Some encouragement to separate things is applied in the form a soft faced mallet.
Things separating nicely.
Bellhousing is removed. The back of the input shaft is what the synchromesh engages with when in 4th gear
Main shaft (upper) and layshaft. The synchromesh (mainshaft) doesn’t look right.
With the constant gear removed it’s clear to see the synchromesh outer frame isn’t sitting centrally.

I have to remove the selector shaft to remove the synchromesh but all 3 springs are missing. One is lodged in the selector. I think this has caused the jamming.