This is my first 1/8 buggy I've built and I can't figure out how I am getting front gearbox binding to a point that the front pair of tires are locked and cannot spin at all. Individually in the front when I rotate one the other side rotates freely in the opposite direction as normal.

When I remove all 4 chassis screws under the front gearbox this loosens it enough to a point where the front pair of tires can now roll (but with a lot of resistance).

When I roll only the rear pair of tires I can see the spur gear turning as well but the front pair of tires are not moving. You can see the center diff's front output trying to turn but it seems to be bound up by something in the front gearbox/diff.

This is very strange as I followed all the instructions clearly...it must be something in the front differential when the buggy is trying to roll forward. But if that was the case how would removing the 4 chassis screws for the front gearbox allow the buggy to somewhat roll forward??