First off you never want to try shifting without using the clutch, unless your driving your ex's car... Be that as it may with a synchro mess transmission you can shift without the clutch in and out but again dont make it a habbit. My truck recently had the transmisson replaced. When you go to a stop light put the truck into neutral, sit a few seconds, and then try putting it back into gear. If there is any kick back or grinding you have issues. The Xterra 5spd is known for issues with the synchros. The whole transmission wont go but shifting becomes hard and eventually the gear will go. I had to try and try and finally went to another dealer to get my transmission replaced, under warranty. I struck a good deal with the service manager they would fight for the new transmission if I agreed to put in a new clutch. The labor for the clutch was covered under the transmission repair and I only had to pay for parts about 500.00$. They also threw in the rental for me. Talk to the service manager and see what you can do. Dont try calling Nissan they will side with the dealer. You may have to find another dealer in your area. Hope this helps let us know what the outcome is.
Tim
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"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrannts."
Thomas Jefferson