And then there were four.... Gears, that is....

[KevR]

Trolling along today in fifth at about 60mph, small bang and sudden total loss of drive - I thought the clutch had gone bang, but changed down and all was well. But fifth gear is now missing. Anyone experienced this before? Is it likely to be just the pinions on the end of the box under the pressed steel cover? Or something more terminal inside?
All other gears work fine and quietly, there's just a whiny grumble when I select fifth, and no drive.

I've got a spare gearbox and was planning a clutch swap soon anyway, so it's not the end of the world. Would be nice to know what the problem is though. Even nicer if it turns out I'm not risking complete gearbox failure by continuing to drive it with four gears....

[David]

It would only be speculation to assume what is wrong with it, However to me it sounds like the small pin that holds the fork to the shaft has snapped & it has been pushed out of gear. I would be careful the gearbox doesn't lock up if 5th decides to engage while your driving in another gear.
What does the gearbox do if you attempt to go for 5th gear while the engine is stopped? If the gear stick goes where 5th should be but doesn't engage, that will probably be what I have described.
If it is, It is a very easy fix, just pull the cover off & put a new pin in it.

Here's a picture of 5th, The mentioned pin is just out of the picture, in the brass fork/steel rod at the top.

Hope that helps.

[KevR]

Yes, that helps. Haven't tried to put in 5th with engine stopped, but if I try to put it in fifth with engine running the lever goes where it should, and some random whirring/grumbling occurs. No graunching or sounds of mechanical mayhem.

[Vanny]

Just to double check, will it go into reverse?

If you've lost 5th and reverse, it might be the reverse idler shaft has become free, but i think David has it right.

[KevR]

Reverse is fine - only fifth that's missing!

[KevR]

Had the cover off,and the nuts on both the shafts were loose on their threads - still peened over but loose. Don't have a 28mm 12-point socket so can't take them off to look properly yet but it appears the smaller of the two pinions (or its shaft) has stripped its splines.
Bugger.
Gearbox out tomorrow. I've been promising it a new clutch for the last 25,000 miles anyway, so at least I can do that as well as fitting the spare gearbox and various other bits and pieces.