Hinges for toilet seats and covers come in two basic materials, plastic and metal. Plastic hinges are typically moulded into a one-piece design that is permanently attached to the seat or cover. This makes the plastic hinge economical, but almost impossible to repair as the entire seat and cover assembly must be replaced. Metal hinges, on the other hand, come in a multiple-part assembly. The hinges are attached to the seat and cover separately with machine screws. A long hinge pin attaches the separate hinges together. This allows for quick removal and repair of the separate hinge pieces.
Remove the toilet seat and cover from the toilet bowl. Loosen the rear main screws of the seat hinge assembly, by turning them in a counterclockwise direction. The nuts for the hinge bolts reside on the underside of the bowl. Lift the entire assembly from the toilet bowl.
Lay the toilet seat and cover on a flat and firm surface. Remove the broken hinge assembly from the seat or cover. Loosen the four screws, generally two screws per hinge, from the appropriate cover or seat. Lift the hinge assembly from the seat.
Identify the main hinge pin that attaches the four sets of hinges. The hinge pin is round and approximately 1/4 inch in diameter.
Set the thin end of the nail punch to the centre of the long hinge pin. Strike the end of the punch with the small hammer. The stem will move out of the hinge assembly.
Adjust the jaws of the pliers around the end of the exposed hinge pin. Carefully pull the hinge pin from the sets of hinges. There may be no need to remove the hinge pin completely if only one hinge requires repair. Pull the pin until the broken or problem hinge is loose and accessible.
Apply some wax to the hinge pin for stiff-acting hinges. Run a single round of cellophane tape around the end of the hinge pin for loose fits.
Place a single drop of instant glue on broken parts of the hinge. Hold the parts together and let the glue set-up. Follow label directions for drying times and application rates of the instant glue.
Replace the hinge with an identical mate if repair is not possible. Insert the hinge pin. Install the seat and cover back onto the toilet bowl.
Due to the many styles of metal toilet seat hinges, you may want to take the broken hinge with you for correct identification. Most home centre stores carry a large variety of hinge replacements.