Introduction
A slipping mainspring or sudden loss of power is one of the most frustrating problems in mechanical clock repair. Whether the spring is in a barrel or open, the cause is usually related to hook wear, lubrication issues, or sticking coils. This guide explains the most common reasons mainsprings slip and how to diagnose each one safely.
Check the Barrel Hook
Inspect the barrel hook for wear
If the barrel hook is rounded, worn, or broken, the mainspring will slip when winding or under load.
Check for hook deformation
A hook bent outward or inward may fail to catch the inner coil properly.
Verify hook height
If the hook sits too low or too high, the spring may not seat correctly during winding.
Check the Arbor Hook
Inspect the arbor hook for rounding
A worn arbor hook will allow the spring to slip during winding, causing sudden loss of tension.
Check for cracks or fractures
Arbor hooks can crack at the base, especially in older movements.
Verify proper engagement
The arbor hook must catch the inner coil firmly and consistently.
Check for Sticking or Gummy Coils
Inspect the spring for dried oil
Old oil turns sticky and prevents the spring from unwinding smoothly, causing power loss.
Look for rust or corrosion
Rust increases friction and can cause the spring to bind or slip.
Check for coil set
A spring that has taken a permanent set will not deliver full power.
Check for Power‑Train Drag
Inspect pivots and bushings
Worn or dirty pivots reduce power and make it appear as though the mainspring is weak.
Check wheel freedom
Each wheel should spin freely with the mainspring let down. Binding indicates drag.
Look for bent pivots
A pivot that runs out of true causes intermittent power loss.
Check for Incorrect Lubrication
Verify proper mainspring lubrication
Too much grease or the wrong lubricant can cause sticking and uneven power delivery.
Check for dry coils
A completely dry mainspring will chatter and slip under load.
Inspect for contamination
Dirt or debris between coils increases friction and reduces power.
Recommended Internal Links
FAQs
Why does my mainspring slip when winding?
The arbor hook or barrel hook is likely worn or not engaging properly.
Why does my clock lose power suddenly?
A slipping hook or sticking coils can cause sudden loss of power.
Can lubrication fix a slipping mainspring?
Only if the issue is sticking coils. Hook wear requires repair or replacement.
Why does my mainspring feel weak?
It may be set, dirty, or suffering from internal friction.
Should I replace or repair a worn hook?
Replacement is usually the safest option, but some hooks can be reshaped if not severely worn.
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