Clutch Free Play
Clutch free play & more importantly, "free travel". is crucial for ensuring the proper operation of the clutch disk, fly wheel, and transmission.
Pressing down on the clutch pedal must fully disengage the clutch disk from flywheel. If there is too much free play, the clutch disk and flywheel remain in contact.
Proper set up of clutch pedal and free play/travel will result in smoother, less "clunky", "grinding" shifts. Of course this also has the benefit of less clutch and transmission wear.
In a nut shell, to set the free play, you simply adjust bumper so that the pedal is 8-3/4" ('73 240z, '77 280z) 7.9" (83 280zx) from the floor then release the lock nut and turn the clutch rod to take up slack in the system. (Warning, small hands help!)
When properly adjusted, pressing on the clutch pedal should cause the clutch rod to start moving after the pedal travels within the first 0.5" ('73 240z, '77 280z) 0.2" (83 280zx) towards the floor.
Note: it is wise to use a flashlight and some liquid wrench/pb blaster to help loosen stuck nuts and rods. .
Also laying upside down with your body outside the driver door and head on the floor mat looking up helps!
Foam on the door sill is a nice comfort too!
(Click to enlarge)
Here is a shot looking up from the floor mat (click to enlarge)