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Grandfather Clocks Running Fast Slow Over Time

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Posted May 12, 2009

Is your grandfather clock running too fast or too slow? If so, what should you do about it. This is a question we get asked many times, and we are attempting to provide here a useful guide for most owners of clocks.

Before deciding whether to raise or lower what is known as the pendulum bob - the usually brass round weight near the bottom of the pendulum - it might first worth be asking whether the grandfather clock had been running fine for many years. If so, and it has, say, after 5 or 10 plus years after purchasing it, a slow-running clock may be a symptom of a clock that needs a good cleaning and oiling. If so, find a good local grandfather clocks repair center.

But what if your grandfather clock is new, or you’ve recently moved it, and it needs adjustment? If your grandfather clock is RUNNING TOO SLOW, one should LOWER the pendulum bob to make the clock’s movement run faster. If the clock is RUNNING TOO FAST, one should raise the pendulum bob to make the clock’s movement go slower. One needs to have patience and be willing to experiment with how many turns of the screw beneath the pendulum will affect your clock. Checking against a computer clock or other reliable timepiece once a day is a good idea, as is keeping notes of how many turns of the screw were made and the impact it had on the time.

Another key question is WHAT DIRECTION does one turn the screw beneath the pendulum to raise or lower the pendulum bob. While it does not work the same for all clocks, the large majority of clocks made in the last 50 years will allow one to follow the direction of turning the screw clockwise or right to raise the pendulum bob and make the clock go faster. Conversely, for most grandfather clock movements, if one turns the screw beneath the pendulum bob counter-clockwise or left to lower the pendulum make, it will make the clock go slower.

The best advice we can give is to try moving the pendulum bob a turn for every minute, for, say, up to a 10 minute daily variation vs. the correct time. Recalibrate after seeing the results after 24 hours, and decide what to do the next day.

A final note. We recommend not seeking the perfection of an atomic clock, but rather getting your clock to be accurate within, say, a minute or so per day. After all, another way of looking at it is you can spend $25 for a very accurate quartz watch or many thousands of dollars for a Rolex, Audemars, or Vacheron Constantin. One is buying more than accurate timekeeping when investing in a grandfather clock.