I got to the Chapter of Limbo where there are the two big gears and the lever that reverses which direction they turn in. I am having a lot of trouble figuring it out from there.
Ah! Figured it out! It is a timing thing. The lever reverses the rotation direction of the gears, but there is a slight pause while the gears are switching directions where you can jump up on the one and then get to the other as it switches direction.