Originally Posted by MrHarris
Sure this isn't because we are shifting too fast/hard?
That's what my guess was above--though I put it slightly differently.
When the dog collar disengages from first gear and begins to engage with second gear, the synchro mechanism makes first contact in order to synchronize second gear with the dog collar before the teeth engage. It takes time for this to happen, and the greater the difference in speed between the gears, the more time it takes for the synchro to work. Until things are sync'd, the balk ring keeps the teeth from engaging. But, the balk ring can be overcome with enough force, at which point the teeth will grind.
My guess is that some are shifting too hard and/or too fast, overcoming the action of the balk or blocking mechanism.