How do I move an obstacle in relation to a sloped line? (2D)

I have the following code:

using UnityEngine; using System.Collections;

public class obstacleController : MonoBehaviour {

 private float xVal;
 public float speed;
 private float yMove;
 
 // Use this for initialization
 void Start () {
     xVal = transform.position.x;
 }
 
 // Update is called once per frame
 void Update () {
     xVal = xVal - speed;
     yMove =  xVal * -0.17857687905f;
     transform.Translate(xVal - speed, yMove);
     print (yMove);
     print (xVal);
 }

}

-0.17857687905f is the slope of the line I'm trying to get the object to move parallel to

speed is set to .25

If I use transform.position (blah blah) and I put 2 objects with this script at different y values and run the script, it will teleport them to the same y value and move parallel to the line).

When I use the method shown above, the objects just ping off into the middle of nowhere.

I'm really stuck and kind of new to Unity. Please help. :)