1988 1.6 TD 4th gear issues

[Jk75]

Recently 4th gear is difficult to engage when the engine is running warm, sometimes it goes in, sometimes it slips but it is always fine until we have been running her for 30 mins or so. We asked the garage to have a look at last service but I think they just had a quick look and pass E D I T off as 'one of those things' . We are concerned it might signal something much worse and would rather act sooner than later, can anyone give advice?

[Aidan]

4 or 5 speed ?

[Jk75]

4 or 5 speed ?

5 speed

[Aidan]

could be a linkage issue, something obstructing something when hot or it could be an issue inside the box like a synchro hub or ring problem. If it goes into gear is it popping out or is it you can get it it going up the box cold but not changing down from 5th when you come off the main road , if the later I'd suspect 4th5th synchrohub is cracked. There may or may not be indication on drain plug magnet, if there's one of the synchro key pieces on the magnet that's definative.
a good check through the linkage by someone who knows what they are doing and checking again it when hot and in fault mode to help diagnose for sure

[Jk75]

Thank you Aidan, it sometimes slips going up the box and down from 5th , will get someone to have a good look based on those possibilities. Really useful reply thank you! J