Grinding Fourth

[CdnNavybob]

I've had this problem in my Stang for a couple of years but it's just resurfaced because I haven't done much highway driving in quite a while. I have a 2000 GT (T45 trans).
Under normal conditions I can run it up to fifth and then back down again no problem. Once it's been on the highway for a while (30-45 mins) it won't let me downshift to fourth, it just grinds. If I slow down enough to shift into third, and then go back up to fourth, it still grinds. The only way I can get it back into fourth gear is by coming to a complete stop. After that, I can upshift normally, but as soon as I hit fifth, it'll grind the downshift to fourth again. Any ideas?

 

[Mike97gt]

I've had this problem in my Stang for a couple of years but it's just resurfaced because I haven't done much highway driving in quite a while. I have a 2000 GT (T45 trans).
Under normal conditions I can run it up to fifth and then back down again no problem. Once it's been on the highway for a while (30-45 mins) it won't let me downshift to fourth, it just grinds. If I slow down enough to shift into third, and then go back up to fourth, it still grinds. The only way I can get it back into fourth gear is by coming to a complete stop. After that, I can upshift normally, but as soon as I hit fifth, it'll grind the downshift to fourth again. Any ideas?

not good. sounds to me like a bad 4th gear syncro.

 

[CdnNavybob]

That was my best guess too, but why would it only do it when it's hot?

 

[dcarlson]

That was my best guess too, but why would it only do it when it's hot?

Oil is thicker when cold. Sometimes that makes the syncros grab better. What kind of fluid is in the transmission?

 

[CdnNavybob]

Oil is thicker when cold. Sometimes that makes the syncros grab better. What kind of fluid is in the transmission?

It's whatever Ford uses. The car is still on it's extended warranty so I take it to them for regular maintenance.