Introduction
The suspension spring is one of the most important parts of a mechanical clock’s timekeeping system. It controls the pendulum’s motion, regulates beat stability, and determines how efficiently the escapement transfers power. Choosing the wrong suspension spring leads to poor timekeeping, wobble, or a clock that won’t run at all. This guide explains how to choose the correct suspension spring for your clock.
Understanding What a Suspension Spring Does
Controls the pendulum’s swing
The suspension spring determines how freely the pendulum moves and how much impulse it receives from the escapement.
Sets the beat stability
A twisted or incorrect spring causes beat errors and uneven tick‑tock rhythm.
Determines pendulum alignment
The spring keeps the pendulum centered. Wrong length or thickness causes wobble or scraping.
How to Identify the Correct Suspension Spring
Match the movement manufacturer
Hermle, Kieninger, Urgos, Seth Thomas, and Ansonia all use different suspension styles. Matching the maker is the fastest way to get the right part.
Check the movement number
Modern movements (Hermle, Urgos, Kieninger) have stamped numbers that correspond to specific suspension units.
Measure the old suspension spring
If the original spring is intact, measure its total length, block size, and spring thickness.
Common Suspension Spring Types
Hermle suspension units
Hermle uses standardized suspension assemblies with specific lengths and block shapes. These are easy to match using the movement number.
American clock suspension springs
Many American clocks use simple flat springs with pinned blocks. Length and thickness vary widely.
Anniversary (400‑day) suspension springs
These are extremely thin and must match the exact thickness and length for proper operation.
How to Measure a Suspension Spring
Measure total length
Measure from the top block to the bottom block. Even small differences affect pendulum amplitude.
Measure spring thickness
Use calipers. Thicker springs increase stiffness and shorten the effective pendulum length.
Check block style and pin spacing
Blocks must match the movement’s mounting points exactly.
Common Mistakes When Choosing a Suspension Spring
Choosing by appearance instead of measurement
Two springs may look identical but differ in thickness or block spacing.
Using a spring that is too thick
This causes poor amplitude, wobble, and fast running.
Using a spring that is too long
The pendulum will run slow and may scrape the case.
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FAQs
How do I know which suspension spring my clock needs?
Match the movement number or measure the original spring’s length, thickness, and block style.
Can I use a spring that is “close enough”?
No. Small differences in thickness or length significantly affect timekeeping.
Why does my pendulum wobble?
Wobble usually indicates a twisted or incorrect suspension spring.
Do all Hermle clocks use the same suspension unit?
No. Hermle uses multiple lengths and block configurations depending on the movement.
What happens if the suspension spring is too thick?
The clock will run fast, lose amplitude, and may stop intermittently.
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