Why is my third gear behaving as a pendulum?

I have a three gear system ("small", "medium", and "large gear"), where each gear is connected to the other through a "common gear constraint". the "small gear" and "medium gear" work hand in hand, though the "large gear" even though has a common gear constraint to the "medium gear", tends to act as a pendulum. I did some reading, and I believe that it may have something to do with the reference systems, but cant put my finder on it.

Any advice?

cheers

[Steve Miller]

If you attach the model to your question we could help diagnose the problem.

--Steve