Even though a pop-up drain features only the drain plug and the lever that are viewable from the inside of the tub, the drain uses several other parts to open and close the pop-up plug. When pushing the drain's lever no longer opens the stopper, you must remove the other parts of the drain mechanism from the tub's overflow drain in order to make repairs and adjustments. Pulling the mechanisms out of the tub involves some patience, but making adjustments requires few tools.
Remove the screws that hold the tub's overflow drain cover in place, being careful to not drop them down the drain. Pull on the drain's cover to remove the linkage attached to the cover.
Inspect the linkage and tighten any connections that are loose using a wrench. Replace any broken parts of the linkage, attaching the new part to the linkage assembly.
Turn the nut on the lever's linkage counterclockwise to make the linkage longer. Lower the linkage back into the overflow drain and drive the screws back through the cover to secure it in place.
Push down on the drain lever to raise the pop-up stopper, then grab the edges of the stopper and pull it out of the drain along with the linkage attached to it. Examine the stopper and linkage for loose connections and replace any broken parts.
Twist the nut that connects the bottom of the pop-up drain to the linkage counterclockwise, lengthening the connection piece between the stopper and the linkage. Feed the linkage and stopper back into the drain