Gantry Lifting

Hello, I am having trouble with the gantry lifting. This allows the belt to become vertical between the gantry rollers at the y axis. When this happens the gantry lowers on to the vertical belt trapping it enough to cause belt grinding. How do I eliminate gantry lifting?

Hmmm. Mine is heavy enough that it does not lift.

Thank you for your response. Turns out the gantry was not neccessary lifting it saw shifting. I realize the gantry had to much play between the Y axis. I cut new gantry tubes using the 1/8" guidelines and all seem well at this point.