If a shower faucet squeals when it's turned on or is hard to turn, the solution may be as simple as applying plumber's grease. The main part of the faucet that must be greased is the valve stem in a dual-handle model or the cartridge in a single-handle model. These devices connect to the handle and control the flow of water to the spout. You can grease the valve stem or cartridge with plumber's grease by disassembling the faucet handle and removing it from the faucet cavity.
Locate the shut-off valves that supply the shower with water. The shutoffs may be located behind the shower wall or possibly in another room behind an access panel. Remove the access panel with a screwdriver and turn the valves completely clockwise to close. If you can't find the shutoffs, turn off the main water shutoff for the house, often located near the water heater or street.
Remove the handle that is experiencing the problem by prying off the beauty cap on top of the handle with a flat-head screwdriver and removing the screw in the center of the handle, using the Phillips screwdriver. If the shower is a single-handle model, locate the set screw at the handle base and loosen it with an Allen wrench. Pull off the handle.
Pull off the collar directly under the handle by hand, if there is one. Lift out the washer from around the valve stem or cartridge, using needle-nose pliers. Some models of shower faucets may be washer-less, in which case this step can be skipped.
Fit a valve stem wrench completely over the valve stem or cartridge and turn it counterclockwise to remove.
Grease the valve stem or cartridge thoroughly with plumber's grease and use a cotton swab to smear grease into the crevices. Add grease to the faucet handle cavity to thoroughly lube it.
Thread the valve stem or cartridge into the seat by hand and tighten with the valve stem wrench. Replace the washer and collar if the faucet had one and reinstall the handle. Restore the water supply to the shower.