Big D Z

Ok,

I've done this before but now the truck doesn't seem to allow me to adjust the shift point. Following the guide in the book, it says to turn the spur gear until you can see the shift hub. Ok, no problem.

Now, it says to hold the spur gear and roll the truck until the set screw comes into view.

Well, the problem is that no matter which direction I try to roll the truck, it is forcing the spur gear to turn. I'm not able to hold the spur gear because the force is too strong.

Is there something I'm doing wrong or something I missed??

I remember doing this before and it worked just fine, but now it doesn't seem to work.