Triumph Repair: TR-6, synchros, tr 6

Question
After car warms up I can't downshift to 1st or 2nd gears, the gears jam.
Shifting up is no problem.

Answer
Likely your synchros are worn out; you can try double clutching (depress clutch, remove from gear, release clutch, blip the throttle, depress clutch, put into gear, release clutch.  Synchros are meant to help match the engine rotation to the drivetrain rotation; but if worn, they can't compensate as well, so you have to vary the engine RPM to get the same effect.