How to Adjust a Clock Pendulum. That heirloom mantel clock or stately grandfather clock ticking in the corner really adds warmth to your home. But if your treasured clock doesn't keep time, it becomes just another knicknack to gather dust. When your clock is off, follow these steps to adjust the pendulum.
Set your clock to the correct time, using an accurate timepiece or your computer. Then make sure the clock is wound correctly, set on a level surface and ticking. Swing the pendulum gently to the left to get it started.
Check your clock against an accurate timepiece 24 hours after completing Step 1. Note how many minutes slow or fast your clock is running. If it's within one or two minutes of the correct time, you can stop here; most pendulum clocks aren't designed to be more accurate than that. If your clock is running more than a few minutes fast or slow, proceed to Step 3.
Stop your clock's pendulum. Locate the rate nut, which is found just below the bob (the round weight at the lower end of the pendulum). Some pendulums have two nuts; the one at the very tip of the pendulum just serves as an additional weight, and you can ignore it.
Turn the rate nut gently to the left if your clock is running fast. You should see the bob move down the pendulum and will slow the motion. If your clock is running slow, gently turn the rate nut to the right. This will raise the bob and speed up the pendulum's motion. With most pendulum clocks, one full turn of the rate nut equals one minute, but you may need to experiment.
Repeat Steps 1 through 4 for several days, until you get a sense of how many turns of the rate nut it will take to get the pendulum adjusted correctly. Once adjusted, your pendulum clock should be accurate within one or two minutes each week. Make it a practice to reset the minute hand to the correct time when you wind the clock regularly.