Rotating and moving a ball with a Trigger

I have a ball that is moving forward using addforce, and a disk that serves as a trigger. When the ball hits the trigger its y should rotate to match the disk's y rotation. That part works. Next it should move along its new forward. But instead it moves in a direction between the old and new direction.

I've included the code below, its really not much. As for objects is just a ball with a rigid body, and a disk(shrunken cylinder with a mesh colider) that has a rotation of (0,100,90)

 var rot = 0;
 function FixedUpdate() {
     if(rot > 0){
         transform.rotation.eulerAngles.y = rot;
         rot = 0;
     }
     rigidbody.AddForce(transform.forward);
     Debug.DrawLine(transform.position, -transform.forward * .5, Color.green, 60);
 }
 function OnTriggerEnter (col : Collider) {
     var tran = col.transform;
     rot = tran.rotation.eulerAngles.y - 90;
 }