300zx experts HELP! Weird 4th gear issue

[turbosiavr]

Hi, i'm having an issue with my 93 tt 5speed. When ever I drive on the freeway for 30 mins or longer with minimal shifting (like cruising in 5th gear for 30 mins) it will grind when i down shift to 4th gear. I does not grind on any other gear. It almost feels like i did not press the clutch in all the way but I know I did. The 4th gear grind goes away after I park the car for an hour or so. Then it will be fine when I drive around town with no grinding on any gears.I can only replicate the problem after a prolonged freeway drive with minimal shifting. Any ideas? thank you in advance...

[DCaff300ZX]

Welcome!
That's a really odd one and first time I've heard of this problem.
I do know that on occasions the Z32 trans has synchro issues and usually it's 2nd gear or 4th, so maybe the gears are on the same shaft in the trans plus of course we are talking about a 25 year old car...anyway, I can't think of any other reason for what you describe other than an odd synchro issue. Obviously it's not bad enough to warrant trans removal/repair, but does give cause for concern and watching things carefully from here on...best I can say is to use the car often and try to shift as often as possible in and out of 4th gear for awhile and see if that helps free things up.
Sorry for no more help, maybe someone else has had this issue?

[z.Leinbach]

I have a similar problem when I down shift to fast. But changed the gear oil and its stopped (gotten colder here in Washington state as well)