Recently, Align announced a new main gear hub for the earlier 600 electric and nitro models. They also released a new auto-rotation gear and a new auto sleeve. This new hub is a much better design and results in a significantly smoother auto-gear. However, the old auto-rotation gear isn’t compatible with the new hub, nor is the new auto-rotation gear compatible with the old hub. The old auto-rotation gear and the old hub have been discontinued, so…
If you need a new auto-rotation gear you will need to purchase a new hub.
If you need a new hub, you will need to purchase a new auto-rotation gear.
Another thing to be aware of is that the front tail drive gears for the older models are not compatible with the new “Pro” gears. The new “Pro” models, like the 600EFL Pro, use a different auto-rotation gear and front tail drive gear. It looks like you might be able to use the new gears in the older models, but you would need to buy both gears since the auto-rotation gear is a slightly smaller diameter and the front tail drive gear is a slightly larger diameter and both have a different gear pitch. Changing to the new gears will slow your tail down. The gear ratio of the new gears is 3.85:1. The old gears were 4.25:1. That knocks a thousand rpm off your t/r speed.