There is major thread coverage on this issue over on the "other" forum. Align has come out with an upgrade that incorporates a one diameter 6mm shaft and a new tail hub that fits it.
There are still some issues with the new upgrade. The new black umbrella gears material swells as it cools, and it has to be sanded down before you can get it into the rear bearings without destroying them. Also there is a machining tolerance discrepancy in the shoulder that locates the new shaft in the tail box. It is too short by about .1 to .2mm and allows the shaft to move side to side. Kyosho makes a shim set that is sold by A Main that has .1, .2, and .3mm 6 x 8mm shims for around 5 bucks. That will fix the end play issue.
Another thing that everyone is finding is that the chordwise cg on the stock tail blades is off and they are heavier than other aftermarket blades. In some cases as much as 1.5g. Due to the speed of the tail, this is causing a harmonic vibration in the tail that weakens the old step down tail shaft right at the point where yours broke.
I have been running the new tail on three different helis, and it looks like the fix is working for me.
Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
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