As others have said, make sure you check ALL the bearings. We got an AndyMark supershifter (uses some of the same bearings as the kit boxes). It was dragging and hard to turn - imagine our surprise when we found a totally bound up bearing inside it. Luckily we were able to replace the bearing with one from the kit transmissions and we're driving again.
It was very curious when the bot kept wanting to turn right
