Get the sin of an angle between vector3.forward and direction character is moving

I am trying to make a script that controls my animations based on the characters velocity in a direction compared to the local forward to that character. I am converting from a system that changes the animation based on button presses for two reasons:

1) When I convert to multiplayer there will be less data to synchronise if clients can determine an animation based only on an objects facing direction and velocity. 2) By getting the direction and velocity and sending them to mecanim I can smoothly blend between my animations, as I have a blend tree set up that makes the animations nice for situations like: character is moving forward and left, blend the walk forward and walk left animation.

For context this is a 3D FPS game

anyways this is how I am trying to do it, and forward/back velocity works perfectly, but I am getting -1 for my direction no matter what. (Directions set up to blend : 0 is forward, -1 is left, 1 is right)

I am pretty sure it is a problem with my math in the part where I calculate direction, any tips?

Edit: Possible problem I found, the character is walking over uneven terrain so there is a y component to the velocity sometimes. --- I figured out how to get rid of the y component so direction now only has a x and z component.

Calculate forward velocity:

 forwardVelocity = transform.InverseTransformDirection (GetComponent<CharacterController> ().velocity).z;

Calculate direction:

 direction = transform.InverseTransformDirection (GetComponent<CharacterController> ().velocity);
 animDirection = Mathf.Sin (Vector3.Angle (Vector3.forward, direction2d) * Mathf.Deg2Rad);