Broken guitar tuning pegs usually require replacement rather than fixing. Tuning pegs, also called machine heads, tuners, or tuning keys, can become damaged from accidental impact, or use of tools rather than fingers to turn. Plastic knob pieces on older instruments can dry out and crack from age and environmental factors, or screws can become loose and fall out. Numerous companies manufacture replacement tuners for every instrument, and most local music stores carry a wide selection. With a few basic tools and careful measuring, fixing guitar tuning keys by replacing them is a fairly simple operation.
Remove all guitar strings by turning the tuner with a peg winder or fingers.
Remove the retaining screws from the tuners on the underside of the headstock, with a small flathead or Phillips screwdriver, and put aside.
Identify the bushing type by viewing it from the top side of the headstock. Concentric bushing are pressure mounted, and threaded bushings are hexagonal.
Remove hexagonal threaded bushings by turning counterclockwise with an adjustable wrench and put them aside. The tuners will now push out from the top easily.
Remove pressure bushings by pushing the tuners out through the top of the headstock, and inserting a small flathead screwdriver through the underside of the headstock, pushing up against the bushing side with moderate pressure.
Measure the centre of each hole to the next if the guitar is equipped with three or six inline tuners. If equipped with individual units, measurement will not be necessary.
Contact your music retailer with all measurements and descriptive information. Bringing the old tuners to a local music store will ensure an exact replacement fit.
Slide the new tuners through the underside of the headstock in position, lining up the screw holes.
Install the screws with a Phillips or flathead screwdriver. Screw holes that have become stripped, or are too loose for the new screws, may be filled with a piece of toothpick coated in carpenter's wood glue prior to installation of screws.
Replace bushings by pressing in pressure bushings with fingers, or tightening threaded bushings clockwise with an adjustable wrench.
Tighten underside retaining screws once again, but avoid over-tightening.
Restring guitar and bring up to pitch.
Drilling new holes, or widening old ones to accommodate non-standard tuners, should be done by a professional guitar repair person.