Drivetrain 07 Mustang GT TR3650 3rd Gear


New Member
Nov 17, 2020
Clarksville, TN
TR-3650 in a 2007 Mustang GT. 179K miles. Fluid already changed fresh couple weeks back with Royal Purple. Shifter was changed out with the Hurst Billet Competition Plus Shifter. Goes in to 3rd with ease (still very notchy though) when transmission is cold, does not go in when transmission is hot. Cannot double clutch it, I've tried (and yes I am able to flawlessly double clutch every other gear). If I go into neutral and try to go straight up to 3rd I hit a wall. If I try to quick shift, it grinds but goes in. The only way to get it in when hot, without grinding, is to shift very slowly or rev to 6k RPMS (don't ask me, I really don't know, but a third gear downshift, blipping the throttle to match the perfect RPM for 3rd gear, it STILL refuses to go in gear).

I know the likely answer is 3rd gear synchro is absolutely toast. I know the best option is to take it to a shop to get rebuilt. That's a $1500-$2000 job and that money has to go to a LOT of other places before fixing 3rd gear. But my question remains: is there anything I can do, right now, to supplement the transmission to make it where I can shift into 3rd again after driving for a single hour? Change out shifter for Steeda Tri-Ax, MGW or Barton? Change fluid back to Motorcraft or go Mobil 1? CHE K-Member Brace?

Btw, this happens at any RPM variation in 3rd. No, I am not always attempting to power shift or slam it into gear. This occurs the worst when I have driven down to the city after an hour, and shift between 2nd - 3rd or downshift from 4th - 3rd. Only 3rd gear.

If it was the synchro, wouldn't it be all the time at any temp? Or am I just stupid?
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