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I have a Grandfather Clock...according to the cast iron chimes mount...its over 100 years old...I remember it as a child ...anyway it's been in storage for a long time.

Recently got it working ...keeps excellent time and remembers the last hour chimed,

However...to get it on time correctly I had to shorten the pendulum rod an inch.

I guess this was caused by the change in the earths magnetic field.

Possible Cause	Explanation	Likelihood / Typical Fix
Pendulum bob slipped down	Most common after long storage/moving. Bob slides on rod → effective length increases → clock runs slow.	Very high – fixed by raising bob or shortening rod
Old oil gummed up	Dried lubricant adds friction → escapement loses power → behaves like longer pendulum.	High – needs cleaning & oiling
Wrong pendulum reinstalled	Someone in the past replaced with a longer pendulum (common when parts get mixed up).	Moderate – permanent rod shortening fixes it
Change in Earth's magnetic field	Not the cause. Magnetic field changes are far too weak and slow to affect a brass/steel pendulum in any measurable way.	not likely – no effect on mechanical clocks

spokes,

We have an accomplished professional family member who is gone now; he was always a master carpenter, and when in a long retirement, proved his competency by gifting all manner of wonderful carpentry gift items to even extended family.

A few received incredible grandfather clocks.

Apparently, your overall calculus to effect a correction is evident!

Grandfather Clock Diagnosis Table
Why the Pendulum Had to Be Shortened 1 Inch
Possible Cause Explanation Likelihood / Typical Fix
Pendulum bob slipped down Most common after long storage/moving. Bob slides on rod → effective length increases → clock runs slow. Very high – fixed by raising bob or shortening rod
Old oil gummed up Dried lubricant adds friction → escapement loses power → behaves like longer pendulum. High – needs cleaning & oiling
Wrong pendulum reinstalled Someone in the past replaced with a longer pendulum (common when parts get mixed up). Moderate – permanent rod shortening fixes it
Change in Earth's magnetic field Not the cause. Magnetic field changes are far too weak and slow to affect a brass/steel pendulum in any measurable way. not likely – no effect on mechanical clocks

Re: Grandfather Clock...

~~~~~~~~~~~~~~~~

Reminds me of the old Allan Sherman song...

“...My grandfather’s clock was the best ever made
By the Timex company
Just like the clock John Cameron Swayze displayed
Last night on the old TV

Oh, it works underwater so perfectly
And still makes a ticking sound
Which my grandfather tried only this afternoon
And that’s how the old man drowned...” 🕰️

🐷

I have a grandfather clock too but mine isn’t as old as yours. It was my very first major purchase as an adult. I occasionally have to adjust the weight on the pendulum to slow or speed it up when it gains or loses a minute or two. The reason that happens is mysterious to me. I’ve been assuming it’s a mechanical problem with the clock, or people coming and going in my main entrance hallway throw it off with vibrations on the floor or wind/breeze currents. My long-time clock servicer died and I called the next one nearest to me back in May. He said he could service my clock … in February 2026! And he said he’d only be coming to take the clock back to his shop for a complete workover and oiling/service. I already know how much I’m going to miss the quarter-hour chiming while the clock is gone. If anyone is looking for a new career, may I suggest clock repair? There seems to be a shortage of people who know how to do this.