Hard to shift after being on freeway for a while
 

Hi everyone,

Got this weird problem with my 1981 manual transmission. I recently replaced the transmission seals and fluid (redline) and everything shifts normal when driving town with about 40-50mph and occasional stops. Whenever I drive on the freeway and I'm on 5th gear for about 30 min. straight, shifting becomes really hard on all gears. There's no grinding but it feels like all gears are very tight/sticky when changing gears. When transmission cools down for a bit it goes back to normal again. I checked the clutch when I put the transmission down and it seems ok.

Any ideas? Thanks!

What weight gear oil did you use? Have you checked the clutch master fluid level / color? Tried bleeding the system?

I used the Red Line (50304) MT-90 75W-90 GL-4 Manual Transmission for the fluid. Also, before I changed the fluid, the issue was already there.

Clutch fluid has been full but I haven't chcked the color yet. Will try and bleed the system.