Nissan Repair: 86 nissan d21 wont shift while running, nissan d21, clutch

Question
My '86 nissan d21 won't shift in or out of gear while its running but will shift just
fine when its not running?

Answer
Hi Chaz -

Can you shift it into second or third gear while running? What about reverse? Or is it only 1st gear.

Is the clutch pedal easy to depress?

I am thinking it is either the clucth master system, or the transmission sync.
Depends on what you answer above -

Please let me know -
aloha
calvin