Hi

I have found that after driving for a while and when the engine gets up to full temperature it becomes increasingly difficult to change gears - the clutch pedal is literally floored and it’s still difficult

Once everything is left to cool down , gearchanging becomes normal again.

Any ideas?

How is your clutch pedal free play?

If it is insufficient or gone entirely, when stuff heats up, it could decrease enough to make your clutch slip and heat up, making things worse

If you are not familiar with clutch free play, do some research.

MANY people do not understand clutch free play.

How's the oil level and how old is the oil and what type of oil?
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

IRL;

I didn't think of the internal lube as Eric has...the first thing I thought of was a stretched/stretching Clutch Cable, but I don't know, nor can explain, how this might be so thermally dependent.

I suggest you have a look at the Throughout Fork under the car, and have a helper depress the Clutch Pedal, and compare the action when cold, to the action when hot...there should clearly be similar amount of movement...if less when hot, that's a big hint!

See also: https://www.sw-em.com/Clutch_-_cable_actuated_Notes.htm

Good Hunting!

Does the ‘71 have a hydraulic clutch? If so could it be partially failing when the fluid gets hot?

Chris;

No Hydr Clutch actuation on a '71...that was one of the major changes which came along with the D-Jet injection in '69...

Cheers

I see. Thank you.