Synthetic transmission fluid for a manual transmission?

[Old Tele man]

...correct, it's common to wear/chip synchro "teeth" but not the actual mechanically-engaged gear teeth...to break one of them usually means a piece of hard metal (brass might do it, but usually not) has broken loose from something and physically gotten between the engaging gear teeth, which if you notice in the illustrations, are always engaged with their mating gear...all engagement is via the synchro.

[Christ]

If someone told me that the teeth broke off the gear, I'd assume they meant the helical splines that engage from gear to gear, which transfer power between gears.

Probably the furthest thing from my mind would be the dog-teeth, or those things that engage the gear to the input/output shaft (whichever one free spins when gears aren't engaged, usually output, I think) so that it can begin transferring power from the input shaft, to the drive gear, which sends power to the driven gear (via the "teeth" or Helix Splines), which sends power to the output shaft, eventually going to the differential and driving the wheels.

The fact that you're getting an easily reproducible grinding noise suggests that you've destroyed a synchronizer, though.

[Old Tele man]

Originally Posted by Christ

The fact that you're getting an easily reproducible grinding noise suggests that you've destroyed a synchronizer, though.

...my diagnosis too. But, if there REALLY are pieces of "iron teeth" in there, that's BAD news.

[Christ]

Originally Posted by Old Tele man

...my diagnosis too. But, if there REALLY are pieces of "iron teeth" in there, that's BAD news.

Most definitely. In fact, I'd be inclined to say that if there are pieces of anything in there, trouble is afoot.

[Old Tele man]

...both require tearing down the tranny, but IMHO swapping in new synchros is much easier and less costly than changing out a mating gear-set (because, then you really should refresh all the synchro too...ultimately too much money).

[Daox]

I used Redline in my 03 Matrix (came with it when I purchased the car), and I have Royal Purple in the Paseo. When I put the Royal Purple in the Paseo, it made a noticeable difference when the car was cold in the winter. It wasn't noticeable in the summer. I'd still highly recommend synthetic, whatever brand you go with.