Not the usual clutch problem.

The clutch on my F is low. It was very low. The system has been pressure bled twice and this evening I removed the clutch damper valve which has improved the feel and raised the apparent biting point to an inch off the floor. Last week, the slave cylinder was checked and found to be fluid tight beneath the boot. At the same time, the operating arm was verified to be free by removing the clevis pin and moving it by hand without resistance.

The slave cylinder begins its travel as soon as the free play in the pedal is taken up. There is little doubt that there is no air in the system, or that the mechanical linkages are good. Comparing the free play at the pedal, about 1/4", against that of a new clevis pin in a new clevis shows a very similar amount, ruling out an excessively worn clevis. There is no noise from the clutch release bearing and the clutch frees off completely. It is just very low.

I am beginning to think that one of the master cylinder seals may be failing. There is no external leakage,and a liquid pushrod has no compressibility (assuming that the flexible pipe is sound, of course.) Having eliminated all the other possibilities I can think of, I am going to fit a full repair kit to the master cylinder. I think the upper seal is worn and not fully efficient and might be losing pressure back to the reservoir. The lower seal, being all right, seals the bottom of the cylinder so it doesn't leak. If that doesn't fix it, though, I shall be stuck!
The car has covered 70,000 miles and the clutch cannot be made to slip.
Can anybody think of anything I might have missed?

In my experience, having the clutch engage when the pedal is only an inch off the floor indicates a worn-out clutch. The clutch in my wife's F was acting the same as you are describing and I found the clutch worn down to just above the rivets.

I concur with our learn’d friend Mowog, my clutch did the same when it shat itself!

Certainly what I would have thought but the general consensus here is that the pedal gets higher when the clutch wears out, hence my confusion.

It didn't on mine.

I wonder if that is cause or effect. Worn diaphragm fingers make a clutch notchy and hard as well as low but clutch plate wear will cause the fingers to move out towards the thrust bearing and that would give a high pedal. A low pedal might accelerate wear as the clutch will not fully disengage.

I don't have a picture to reference but I do not recall any significant wear to the diaphragm fingers.

Prior to replacing the clutch in our Toyota Matrix a couple years ago, the clutch would engage when the pedal was only slightly off the floor.

The master cylinder has a wear ring in the bore. It doesn't appear to extend as far up as the upper seal, so I have fitted the repair kit for now and ordered a new cylinder, due Tuesday, so I will be cutting it a bit fine for Thursday. Update: the clutch has been bled and it feels firmer earlier in its travel. Looking forward to trying it later.

No, the clutch is not worn out. The pedal is appreciably heavier but the engagement is 2 1/2" off the floor and the engagement is smooth and progressive. Happy with that.