I have had an intermittent problem with engaging and disengaging gears, which is immediately solved by switching off the engine. If I wait for a minute , then restart, everything works normally for several days, until it happens again. Clutch appears to be working normally, but I have noticed that the gear change gets stiff just before the problem occurs.

I have seen several people reporting this issue. Has anyone solved this problem satisfactorily?

It will be either the clutch master cylinder OR the clutch slave cylinder that is starting to fail.

Much easier and cheaper to replace the master cylinder first and see if that fixes the problem.

Thanks for your helpful post, but what puzzles me is why the problem is so intermittent? If the hydraulic system is starting to fail why does it then work perfectly for a week or more?

well, you have to start somewhere = I would suggest you start with the cheapest, and easy possible fix first and do what Unofix recommends

I take your point. I was actually going to start first with the gear change linkage, because that's easy and cheap to access.

19 minutes ago, Haydron said:

I was actually going to start first with the gear change linkage,

Why would switching off the engine affect the operation of the gear change linkage ? 🤔

I can't see any direct effect other than, possibly, the stopping of the engine slightly reducing the load on the linkage. On the other hand, does stopping the engine affect the operation of the master cylinder? One other suggestion is that the clutch plate is sticking to the flywheel or the release plate is faulty?

1 hour ago, Haydron said:

On the other hand, does stopping the engine affect the operation of the master cylinder?

The likely problem is the seals in either the clutch master or slave cylinder are starting to fail. Depending upon how much the clutch pedal has been used on a particular journey, and depending on the temperature, particularly of the slave cylinder, it will effect how much of the hydraulic pressure is being lost when the pedal is depressed. This means that the clutch plate is not fully disengaged and you are effectively trying to change gear while the engine is still connected to the gearbox. Stopping  the engine means that the gears can easily be changed regardless of the operation of the clutch.

The more common failure is the clutch slave cylinder because it is mounted inside of the bell housing and it gets very hot. However to replace that means the gearbox has to come out, and when it's removed it is always good practice to fit a whole new clutch. It's a time consuming and expensive job, therefore most mechanics would change the master cylinder first.

Thanks Unofix , a very helpful explanation. I'll start with the master cylinder as you suggest.

I'd love to know how @Haydron fixed this - I have the same problem. Wife's car. Caused confusion for me for the same reason. Simply turning off the engine and restarting ( even for 1 to 2 seconds - not even a minute ) resets the issue - which is very weird... Also heard it could be due to the lower linkage in the gear selector - something else to look into...

I drove it to work this morning to see for myself and it started to get "stiffer" in changing for the last 10 minutes of a 30 minute drive, then failed completely, especially to first or second, and reverse was out of the question... Made it in, couldn't select first in car park. Found the plate sticking - that is, if it was in first or second and clutch down, and I had the brake on, the engine started to stutter like the clutch wasn't fully down. But yeah, once "reset" by the magic turn off/ turn on the clutch fully worked again. I can't understand the symptoms either.

The connection is obviously the fly wheel stops turning, so somehow the clutch plate is also sticking, but I'm unsure why this makes such a difference? Warped plate? Collapsing pressure plate ? Thrust bearing issue? I'm not sure either. Seems it's age related in old Fiesta's. Also doesn't ever happen from cold or restart... Only after driving a while.

Any good videos on fixing this without having to go to Ford? They are very poor in their service in Australia.