[Kevin Sevcik]

The axle holes in the C-Channel aren't exactly in the center of the channel. When you assemble everything, this means the holes are closer to the top or bottom of the frame. One or two of the channels on your tight side might be upside down relative to your loose side. The easiest visual check is to look at the one hole that's out of line with the rest. Make sure it's shifted in the same direction on all your channels. The correct direction is probably down, which puts the rest of the holes closer to the top of the frame.