There are four pulleys on a garage door extension spring set-up, two bolted in a stationary position above either side of the track's curve, and two pulleys with yokes attached to the springs on either side of the horizontal track. To detect wear, you should take the spring tension off the pulleys. You do this by opening the door fully until the spring begins to droop down. Put a clamp on the track to hold the door up.
If you have a garage door opener, unplug it to prevent accidental activation while the door is in the open position!
There should be very little movement in the pulleys except their rotation. If they do not turn smoothly or wobble, replace them.
