As the title states my srt4 go smoothly into all other gears but it will not go into 3rd as soon as you put it in third and let the clutch out all you hear is a terrible grind noise. So I took out the gears and I still can’t really identify any issues with them I though I’d spot some serious metal shavings but I haven’t found any? While I have out the gears I’m also putting in straight cut first and second is there any downside to this.
I would check your synchro rings. My 3rd used to grind horribly unless you matched the RPMs perfect. I pulled my gear set out and everything looked perfect except the lining on the 3rd gear synchronizer was wiped out. Replaced it, threw it back together and it shifts beautiful now.