Rewind two years ago to when we were trying to figure out a fix for poor shifting on the FRS/BRZ AZ6 transmission. We contacted Synchrotech Transmissions for their carbon synchro technology but sadly, at that time, the market was not large enough to invest the time and money into a solution yet.
Fast forward to today, we've been driving with these synchros (currently on sale!) for a few weeks now. With multiple drives, both long and short, easy and hard, under their belt, I can begin to comment on their behavior and
I'll go over cold and hot results separately. If your transmission is anything like mine, the two conditions shift entirely different. All tests were done with 75w-90 Neo Synthetic gear oil to date. When I say "grind", I don't mean fully locked out of gear but more of a crunch to get into gear. It results in a not smooth shift as the dogs of the gear do not fully match the shift ring selector when trying to go into gear. This crunch/grind is a result of the synchronizer not matching the gear's speed to the shaft's speed when you go to shift into gear.
Before: With the OE synchros, it was basically a sure thing I was going to crunch/grind going into 2nd. If I shifted quick enough when cold, it would crunch or grind, if I tried to shift slow, it would almost act as if I were locked out of gear. I would have to put a lot of muscle into it. Maybe 10% of the time I could get into 2nd without a grind when the transmission was cold. If I tried to go into 2nd without rev matching, it would again feel like I was locked out of gear. 3rd gear was much like 2nd, but probably closer to a 50/50 split of grind/no grind when cold. 5th gear was also very blah when the transmission was cold. 50/50 split of grind/no grind when the transmission was cold.
After: 2nd grind/crunch is almost gone. I'd say I can avoid any audible crunch/grind 80% of the time which is substantially better than the OE synchro! It's night and day difference in my opinion and well worth the upgrade for this alone. I *hated* 2nd gear when the trans was cold before. 3rd grind is completely gone. Shifts are smooth.-5th crunch is almost completely gone. I think I've hit the crunch zone 1-2 times.
TLDR Cold Behavior: Significant improvement throughout. The gears that used to grind have almost been completely resolved. The other gears shift smoother and easier when cold as well.
Before: 2nd, 3rd, and 5th were still the problem children for me; however, when warm it was significantly better than cold. I could avoid grinding/crunching most of the time.
After: Shifts like you'd want any car to shift. Smooth, clean, goes into gear every time without any fuss. I'm thrilled. Downshifts are amazingly smooth even at 5-6k RPM. Upshifts are great at redline, even better than slower RPM shifting.
Dave from Synchrotech also got me a few bottles of their specific fluid that I will be testing out as well! Hoping that may resolve ALL of the shifting issues even though I am very happy with how the car shifts right now. I'll continue to update as I put more miles on the car.
Thanks and as always, let us know if you have any questions!