Crouch + Jump Problem

Hi i have script for jump and crouch

crouch function is changing collider's y scale here is the code

     function Update()
     {  
        var ultScale = tr.localScale.y;
         tr.localScale.y = Mathf.Lerp(tr.localScale.y, vScale, 5*Time.deltaTime);
         tr.position.y += dist * (tr.localScale.y-ultScale); 
     }
     function Crouch()
     {
         vScale = 0.5;
     }

Here is my jump code:

 function Start()
 {
     distToGround = GetComponent.<Collider>().bounds.extents.z;
 }
 function IsGrounded () : booleanTrue/False
 {
     return Physics.Raycast(transform.position, Vector3.down, distToGround + 0.1); 
 }
 public function Jump()
 {    
     if (IsGrounded() && canJump == true)
         {
         GetComponent.<Rigidbody>().velocity.y = jumpHeight;
         playerAnim.SetTrigger("Jump");    
     }
 }

So when i crouch i call this Crouch() and jump call Jump()

The problem is here: After crouching the collider is getting back at it's normal scale (1) and sometimes when i try to jump, the jump function is not working i think the problem is somewhere in the raycast coz when i crouch its shorter idk.. can some1 tell me what is the problem and how to fix it?