My Defender 110 lost 5th gear

So I was driving along, went from 4th to 5th, let out on the clutch and nothing happened. No noise or odd feeling. Just felt empty. I don't know much about gearboxes, reckon it's time to learn. Not sure but I believe it might have an LT77.

What year is it? Lets be sure about the gearbox before we start diagnosing.

His profile page says "1989 Defender 110" so that would make it a 2.5td, as l believe the 200tdi came out in late 1990.

Unless it's had an engine change.

loss of 5th on an lt77 can be for a few reasons
end of layshaft snapped off,circlip failing allowing synchro hub so slide back or pivot come adrift ,you need to remove gear box top to find out

Ok. Yep it has a 200TDI. I will hopefully be able to take a look at it this weekend. I'm assuming to remove the gear box top I'd have to pull it out?

Usually yes. If you remove the gearbox tunnel and then the selector turret, you may be able to see if you are moving the 5th gear selector rod. After that, it's remove the transmission, split the transfer box off, then remove the 5th gear section - it's on the back of the lt77 main box. You'll need circlip pliers and bearing pullers to progress. There are a few good threads on LT77 rebuilds, but you do need the proper tools to strip and rebuild one.

Ok, thanks. I'll give that a try.