It doesn’t have to be gears, but many of the Simulation joints are picky about which order they are applied in. It matters not what order you pick a spur gear, the mathematics are the same. However when you are selecting a internal ring gear, or a worm, then it matters.
Joint Selection Table
I like the graphical Joint Selection Table for most of my Joint applications. It is easy to see and well organized.
If you are still struggling with the Insert joint dialog pull down then check out the Selection table.
Animated Insert Panel
The animations are not just cutely representations for your amusement, but the order that they depict is the key to success here. Take a closer look and watch them.
They depict an order, and that is the order they should be selected in. You can’t feed Inventor a worm when it asks for a gear, and then expect good results.
You have to play by the rules, and these panels are a great method to deliver the steps to first timers as well as reminders for people like me that forget things.