How to adjust or replace a shower door
When sliding doors don’t glide smoothly, repair them. A door that drags on the lower track will eventually do permanent damage to both the door and the track. A dragging roller at the top of the door will wear and require replacement.
First, make sure the rollers on both doors are riding on the tracks inside the upper rail. Sometimes, one roller falls out of the track and the bottom edge of the door skids along the lower rail. In that case, you only have to lift the door and guide the roller back onto the track.
If an off-track roller isn’t the problem, you’ll have to remove the doors to adjust and possibly replace the rollers. Many doors have a small plastic guide at the middle of the lower rail. To remove this type of guide, just remove a single screw. Others have a guide rail screwed to the door.
With the guide removed, lift the doors out of their tracks. Then make sure the rollers turn easily. If not, apply a little WD-40 spray lubricant. Some lubricants can harm plastic, so check the label.
If the lubricant doesn’t do the trick, replace the rollers. Most hardware stores and builder's merchants carry replacements, or try and get in touch with the manufacturer or supplier for the model of shower you have. Take an old roller with you to find a match. In many cases, you can use a replacement that’s slightly larger or smaller than the original. But be sure to check the original and replacement edges match - either rounded or flat.
1. Unscrew the guide at the lower edge of the sliding door. Protect the shower or tub from scratches with a drop cloth.
2. Lift the door out of its track inside the upper rail. Tilt each door in or out to remove it. Wipe both tracks clean.
3. Raise or lower each door by repositioning the roller in its slanted slot. Loosen the screw to move the roller.
[via family handyman]