How to work on old clocks

Updated April 17, 2017

Old clocks are mechanical clocks that were made more than 50 years ago. Weights or springs supply power to a system of internal gears. As the weight falls, or the spring uncoils, it advances a toothed wheel. The toothed wheel interlocks with other gears that ultimately move the clock hands. The time itself is regulated by the swinging of a pendulum. Working on old clocks consists of maintaining these essential parts.

Look for weights hanging down below the face of the old clock. Wall clocks, such as cuckoo clocks and banjo clocks, and tall clocks, like grandfather and grandmother clocks, possess visible weights. These weights are long cylinders that hang from chains or cables. The weights either hang free against the wall or are suspended inside a long case that is located below the clock face.

Rearrange weights on old clocks that do not keep proper time. Clocks may have as many as three weights, each weighing slightly different amounts. The heaviest weight will normally operate the clock's chimes. Hang this weight on the chime chain, or cable, and the other two weights in any order on the other chains or cables.

Wind up old clocks that do not have visible weights. These are spring-driven clocks, and include most mantel, or shelf, clocks. If the clock keeps winding and does not stop, this is a sign of a broken mainspring.

Open the back of the old clock, using a screwdriver if necessary. Look at the end of the mainspring. Mainsprings are of two types: one has a D-shaped hole at the end, while the other has a round or oval loop. The D-shaped hole attaches to a barrel-shaped piece inside the old clock. The round or oval loops attach directly to the ratchet wheel. The ratchet wheel is the toothed wheel that moves the other gears.

Tie the speaker wire around the entire circumference of the spring if the spring ends in a round or oval loop. This will prevent the mainspring from suddenly unravelling.

Power down the clock by inserting the correct size let-down key into the winding arbor. To power down the clock means to release the tension from the spring. Let-down keys are special devices that are used to turn the winding arbor. The winding arbor is the small hole in the clock face through which the old clock is wound.

Hold the let down key firmly in the arbor and then gradually release it so as to cause the old clock mainspring to gently unwind. Do not let the old clock unwind suddenly, or it will damage or destroy the movement. The movement is the collection of gears inside the old clock.

Remove the mainspring from the barrel or ratchet wheel. If it is damaged, it must be replaced with a new mainspring. Usable mainsprings can be cleaned with a kerosene-dampened cloth and lubricated with mainspring grease.

Install the mainspring in the old clock by firmly attaching the inner coil to the mainspring arbor. Use a mainspring winder to actually wind the mainspring back into position. Close up the back of the clock, using the screwdriver if necessary.


If gears are broken inside of the movement of the old clock, it is best to have the clock repaired by a professional clock maker. Old clocks do not generally use currently available standard movements.


Always wear safety glasses or goggles when working with mainsprings. If the spring is broken it can snap off and cause injury. Take the old clock to a professional clock maker if it is too difficult to work with the mainspring without damaging the workings of the clock.

Things You'll Need

  • Old clock
  • Weights
  • Screwdriver
  • Mainspring
  • Let-down key
  • Speaker wire
  • Kerosene
  • Cloth
  • Mainspring grease
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About the Author

Brian Adler has been writing articles on history, politics, religion, art, architecture and antiques since 2002. His writing has been published with Demand Studios, as well as in an online magazine. He holds a Bachelor of Arts degree in history from Columbia University.