4th gear high rev grinding
 

hello. how are you guys doing? sooo i have a question about fd transmission. i was on the freeway earlier and every time i switch to 4th gear on high rev, i hear a little bit of grinding. sorry. im kind of a new to the car scene community and dont know much about cars but im learning. anyway i tried to play with it a little bit. about 4k or below rpm, clutch all the way down, shift to fourth....smoooth transitioning. around 5-6k and up, clutch all the way down, switch to fourth...grind. any idea what's causing it??? before it happened, i kind of slipped switching to third gear and when i went to fourth on high rev, i heard a grind. thank you guys in advance for the help.

Most likely your 4th gear synchro in the transmission is on the way out causing the grind. It has been happening to me for years now. When was the last time the transmission oil was changed and what too? A decent oil can make a difference.

4th gear synchro? I know the 4-5 synchro has a bad habit of failing but I don't remember the 3-4 synchro being a problem. Mazda redesigned the 4-5 synchro in the mid 90's if I remember correctly.