Thread: Series 3 mainshaft nut

Hi All,
My lt76 gearbox is jumping out of 1st & second, on overrun, often when “lurching” from deceleration to acceleration.
There’s also a bit of a “clunk” when taking up drive (initially thought loose prop shaft bolts). May be unrelated.
Now, online I see many references to the mainshaft nut in the T case coming loose (I did think I’d checked this but maybe not closely enough! Will take a look ASAP).
Many posts say this can be the cause of end float in the mainshaft leading to jumping out of 1/2 gear - but is this true?
However… I see no posts with, “Thanks for that hint; tightened it and all is well”.
Makes me wonder if the mainshaft nut comes loose because of other issues, rather than causes them. I fear a collapsed/worn bushing.
Can anyone confirm that their woes were sorted by reefing it back up to 100ft/lb with a castellated piece of pipe?!
Or is the link between gears jumping out and a loose mainshaft nut a Furphy?
Cheers,
Dave

Update.
The nut was tight! I was therefore very anxious as did not want to take the box out again…
I noticed that the gear stick was “springing” away from the engaged direction. I took off the gearbox oil fill cap (floor out again) and could just get to the selector fork clamp bolt. Undid it and moved it towards the required direct 3-4mm (took up the play in that direction). So far all good! And doesn’t jump out of second!!
The “clunk” was the high/low selector lever, pushed by the new gaiter and a bit loose. Tightened it and yanked on the gaiter and my fears of a loose clutch or something are now behind me!
Thanks people for the input.
I AM, however, still interested to hear of anyone that the loose mainshaft nut issue “resolved other issues” on being tightened!
Cheers,
Dave