character not jumping

 #pragma strict
 
     var jumps:AudioClip;
     var stopfoot :AudioSource;
     var speed =40;
     var jumpSpeed : float = 10.0f;
     var controller : CharacterController ;
     var turnSpeed: float = 90; // degrees per second
     private var moveDirection : Vector3;
 
     function Start()
     {
     
      controller= GetComponent(CharacterController);
     
     }
     
     
     function Update() {
     if(Input.GetKeyDown(KeyCode.RightArrow))
       transform.Rotate(0, turnSpeed, 0);
       if(Input.GetKeyDown(KeyCode.LeftArrow))
       transform.Rotate(0, -turnSpeed, 0);
       moveDirection = Vector3(Input.GetAxis("Horizontal")*10, 1,
     speed);
     if (controller.isGrounded)
 {
     if(Input.GetKeyDown(KeyCode.Space))
     {
     moveDirection.y=jumpSpeed;
         Debug.Log("jump");    
     }
     }
     moveDirection *= speed;
     if(!controller.isGrounded)
     {
         moveDirection.y -= 5*Time.deltaTime;
      Debug.Log("gravity");
        }
       controller.SimpleMove(moveDirection * Time.deltaTime);
 }
  
 function jump()  {  
       
          audio.Stop();
          audio.PlayOneShot(jumps);
          animation.Play("jump_pose");
          yield WaitForSeconds(1f);
          animation.Play("run");
         }
         if(transform.position.y<=490)
                 {
             Destroy(this.gameObject);
                 }

tried adding velocity and not using gravity,non of them works. this is an infinite runner,with player moving constantly with rigid body attach to it.