transmission problem, need help

[Project_S13_180]

i have a 89' 240sx coupe...when i start it up it drives fine, nothing is wrong...but after about 10-15 minutes of driving 3rd gear grinds a little bit when i shift into it, so i have to double clutch so it doesnt grind...think im low on gear oil? i have some 80w90 to put in but its been to damned cold outside to put it in and i dont have a 1/2 inch breaker bar for the drain plug...so what do you guys think? why is 3rd gear acting up after i drive for a few minutes?

[NISTECH]

could be your gear oil. once it warms up it thins a bit. have you changed it lately. Alot of guys have had some success with putting redline gear oil in their manual trans to resolve grinding issues. Give it a shot see if it helps your situation. When you drain the old fluid take a look at how much metal is built up on your drain plug magnet and how much is in the old oil. That is an indication of how worn your trans is. If you can still see the head of the screw holding the magnet to the drain plug and the metal is more like a fuzz rather then slivers you are probably ok wear wise. If there are a lot of lerge metal slivers attached to it and your fluid in your drain pan appears metallic. You are most likely in need of internal trans work.[bearings,gears ,syncros] If thats the case you may also try sourcing a used trans with a 30 day guarantee.