doesnt grind and it only does it in second is taht the clutch or transmission if it is trany could i get that fixed without replacing the whole trany if so how much

Sounds like the sancrinizer gear but let a shop drive it first , get more than one estimate .

tranny syncro is out of place take it to a shop

Nissan (Datsun) makes a good trans, as far as normal driving goes. Now some of the problem is you and some from the clutch and box (trans). The trans you have is not a racing trans. You may be trying to shift to soon or to hard. You can try to double clutch or ease off a little when you make the throw....On the mechanical side, bad clutch or hydraulics. You clutch may be still spinning and not free from the engine. The second gear sinks maybe locking to the gear. You can rebuilt 2nd gear if thats the true problem. If your racing, find yourself a good mechanic and some money.

Synchronizers are going out and probably because you have been taking it out of gear without the clutch (per your question a few hours ago ). Good luck !