Shifting problem HELP!!!!!!
 

I have a 2006 Mazda 3s. It has 45k miles on it. The problem I'm running into is with shifting gears. I bought the car in August of '07, with 12k miles on it. After about a month of driving I was realizing that it wasn't shifting into 3rd well...it would actually grind a little when I shifted, but only in 3rd. I took it to the Mazda dealers and they noticed that the 3rd gear "teeth" were worn down. No other gear was worn down, just 3rd. Since I'd only had the car 3 months, they assumed that I wasn't the culprit for the messed up 3rd gear sprocket. PLus with 12k miles on it, it shouldn't have worn down that quickly. I just assumed the person that owned the car before me drove a bit more aggresively and maybe he/she ground 3rd gear too much. Well about 3-4 months ago I noticed that it was starting to, again, shift into 3rd gear about harder than usual. The odd thing is is that the car would shift perfectly in the first 10-15 minutes of driving it, but after it got warmed up, then would it start "catching/grinding" in 3rd. I took it again to a Mazda dealer, and they did agree that 3rd gear wasn't shifting properly, but that it wasn't a big enough deal to fix. I only have 5k miles left on my warranty. I guess my questions are:

1. is it just my clutch?
2. is there a defect in my transmission?
3. does Mazda not just want to fix it?
4. if it's the clutch, is that even under my warranty?

Well, I am just taking some guesses here, but:
Mazda should fix that under warranty.
Sounds like maybe the sychros are going out in third gear.

I would push them to fix it while it is still under warranty.
If they won't, maybe look at an extended warranty, but make sure it covers clutch/transmission issues.
Finally, as a temporary fix, if Mazda won't fix it, you could try putting synthetic gear oil in the tranny to see if that will help alleviate the problem. It won't fix it, but as a last resort it might help make it more driveable.
just my .02

I'd agree that it sounds like synchos. Speaking from experience with my wife's Mazda 6, the warranty period is not the same as the bumper to bumper for a clutch. But your problem doesn't sound like a clutch issue since it is limited to one gear.