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Mike, Consultant
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I have a Pearl Grandfather Clock, have had it for over 30 years,

Resolved Question:

I have a Pearl Grandfather Clock, have had it for over 30 years, the moon dial never worked. Any suggestions?
Submitted: 5 years ago.
Category: Clock Repair
Expert:  Mike replied 5 years ago.

Hi! My name is XXXXX XXXXX it is my pleasure to assist you.


The moon dial is adjusted by turning it. There would be two reasons it does not move. If it is in the midst of an advance motion by the clock, a pin is engaged in a tooth of the moon dial and if you wait a couple of hours it should move easily. The second reason is that a part such as the detent spring can be jammed and the dial would have to be removed to correct the problem.


Sometimes, the moon dial on a grandfather clock refuses to turn. To fix this problem, open the door, or panel, by the clock face. Find the click spring. The click spring is located just behind the moon dial itself. Pull the click spring back about a half inch from the teeth of the moon dial, and then allow it to fall back into place. The click spring should snap into its correct position, and the moon dial begin turning. Do not force the moon dial if it does not turn. Try setting the hands of the clock back three hours and moving the moon dial forward. If it still does not move, professional assistance may be required.



The moon dial is designed to show the shape of the moon as it appears in the sky, the number alongside it being the lunar date. The numbers on the dial are of the Lunar Calendar and NOT the calendar date. A lunar month has consistently twenty nine and a half days in every month and these are usually lettered in Arabic (English) numerals. The Full Moon always occurs on the 15th day of the Lunar Calendar. If it were a full moon today, the image of the moon on the dial would be centered below the 15 on the dial. There are two moons on the dial and it makes no difference which one is under the 15. Grandfather clock moon dials consist of a round disk displaying two pictures of the moon. A one half rotation of the disk occures every 29.5 days which is one lunar cycle.

If your Grandfather Clock has a moving moon dial feature, follow these instructions. To set moon dial, apply slight pressure with your fingers to the front of the moon dial. Rotate the moon dial Clockwise until the moon is directly below the number 15 on the dial. (See figure 5).


Traditional Moon Dial on a Grandfather Clock

If the moon dial will not rotate, wait 6 hours and try again. Never force the moon dial as it should move easily.
1) Using an almanac, lunar calendar or the chart below to determine the date of the last full moon.
2) Position the moon dial so the moon is under the 15 on the dial.
3) Count the number of days past the last full moon on a calendar.
4) Turn the moon dial Clockwise one click for each of the number of days past the last full moon.


The moon dial is now set and will indicate the proper moon phases as long as the Grandfather Clock operates continuously.

Let's pretend today is the 20th of any month.
Your almanac or lunar calendar says the full moon occurs on the 25 of this month.
(this means the full moon is 5 days away..right?)
Set your moon dial on your Grandfather Clock so the moon is under the 10 on the dial which is 5 days before the 15th day the the dial which is the full moon.

If the Grandfather Clock stops for more than 24 hours, the moon dial will also stop, and must be reset when the Grandfather Clock is started again.

Full Moon Calendar

Full Moon Calendar


One of the most frequently asked questions by new clock owners is, "What is the purpose of the moon dial and what do the pictures
or symbols stand for"? The question itself tells us just how much the world has changed.
Today it is difficult for us to realize just how important the ever-changing phases of the moon were in times gone by. In the late 17th
century, the moon dial was added to most long case clocks so that people could plan ahead for when the moon was full and travel at
night was not so hazardous. Clockmasters endeavored to simulate and approximate the appearance of the moon, in each of its
phases, on the face of clocks.
The arched dial was first used in clocks at the beginning of the 18th century, and presented a real challenge to the makers of fine
clocks. By approximately 1720, moving figures began to appear in this space, figures which moved back and forth with the swing of
the pendulum. Among them were prancing deer, rocking ships, and Father Time with his scythe. At the time, there was no practical
value to this feature on the clock, it was done simply for the delight of those viewing the clock.
After motion had been added in the arch above the dial, the next step was to reproduce the progress of the moon from phase to
phase. The proverbial "Man in the Moon" was used on most dials with a landscape and/or seascape on the other half of the circle. A
rocking ship was a frequent symbol of the sea, with a deer often representing the land.
In our very modern world today, the moving moon section of the dial is more decorative than useful, but it is still a very sought after
feature. Many beliefs concerning the moon and its effects have been recorded. Among them:

  • Sweep the house in the dark of the moon and you will have neither moths nor spiders.

  • Trees planted at full moon will bear fruit.
  • Plant peas and potatoes in the increase of the moon.
  • The number of snows during winter is indicated by the number of days from the first snow in fall to the following full moon.
  • Shingle the roof in the decrease of the moon (between full moon and the next new moon) so the shingles are put on when the

horns of the moon are turned down and will not warp and rise up. The same holds true for boardwalks.


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