I have a 2004 Ford Mustang GT 5-Speed with around 64,000 KM (40,000 Miles). Whenever I quickly shift to 3rd gear I hear grinding. This doesn't happen if I shift slowly and allow the RPMs to come down. It's only happening to 3rd gear. I'm assuming it's the synchromesh. Can this be repaired or am I better off replacing the transmission?
Depends on what you want. You can slow up shifting or even double-clutch to reduce additional wear on that synchro but if you want it to work like new the trans needs to be replaced or rebuilt.
Try checking all your clutch adjustments first. It could be as simple as the hydraulic throw out bearing or it could be synchros like Chuck said. Do not rest your hand on the shift lever as this prematurely wears out the synchros.
