Introduction
A slipping mainspring is one of the most common power-loss issues in antique American clocks, including New Haven 8-day movements. When the spring fails to anchor properly or the click mechanism slips, the movement loses power instantly. This guide explains how to diagnose a slipping mainspring, identify whether the problem is with the spring, arbor, or click, and restore proper power to the movement.
How the New Haven 8‑Day Movement Stores Power
The mainspring
The mainspring stores energy and delivers it through the gear train. If the inner coil slips on the arbor, the movement loses power immediately.
The arbor hook
The inner end of the spring must catch securely on a hook or tab on the arbor. Wear or breakage causes slipping.
The click and ratchet
The click prevents the spring from unwinding backward. A worn click or weak click spring allows reverse movement.
The outer spring anchor
The outer end of the spring must be firmly attached to the barrel or plate. If loose, the spring cannot wind properly.
The pendulum system
A slipping spring reduces power to the escapement, affecting the pendulum rod and suspension spring.
Common Causes of a Slipping Spring
Worn or broken arbor hook
The most common cause. The spring cannot grip the arbor and slips under tension.
Inner coil of the spring cracked or distorted
Damage prevents the spring from catching the arbor hook securely.
Worn click or weak click spring
The click fails to hold the ratchet, allowing the spring to unwind backward.
Outer spring anchor loose
Less common, but causes incomplete winding and weak power.
Incorrect replacement spring
A spring that is too wide, too thick, or improperly formed may not seat correctly.
Diagnosing the Problem
Test the winding action
If the key turns freely with no resistance, the spring is slipping at the arbor or click.
Listen for click failure
A slipping click produces a faint snap or reverse movement during winding.
Inspect the arbor hook
Look for wear, rounding, or breakage. A worn hook cannot hold the spring.
Examine the inner coil
Check for cracks, distortion, or a stretched inner loop.
Check the click spring
A weak click spring allows the click to bounce or fail under load.
Correcting the Problem
Repair or replace the arbor hook
If worn, the hook can often be reshaped. If broken, the arbor must be replaced or re-hooked.
Replace the mainspring if damaged
A cracked or distorted inner coil cannot be repaired reliably.
Service the click and click spring
Clean, tighten, or replace the click spring to ensure positive engagement.
Secure the outer spring anchor
Ensure the outer end of the spring is firmly attached to the plate or barrel.
Verify proper spring dimensions
Use the correct width, thickness, and length for the New Haven 8-day movement.
Troubleshooting Flowcharts
If the spring slips during winding
Check arbor hook → Check inner coil → Check click → Check click spring
If the clock winds but stops quickly
Check click → Check pivot wear → Check escapement → Check pendulum clearance
If the spring feels weak
Check outer anchor → Check spring condition → Verify correct spring size
If the pendulum swing is weak
Check power → Check escapement → Check suspension spring → Check rod alignment
If the click snaps or bounces
Check click spring → Check ratchet wear → Check arbor seating
Common Mistakes to Avoid
Reusing a damaged mainspring
Cracked or distorted springs will fail again.
Ignoring click wear
A worn click is dangerous and can cause sudden unwinding.
Using the wrong spring size
Incorrect dimensions cause slipping, binding, or excessive power.
Over‑oiling the spring
Oil attracts dirt and causes sticking. Springs require proper cleaning and lubrication.
Forcing the winding key
Forcing can break the arbor hook or damage the click.
Checklist for Final Verification
• Arbor hook secure
• Inner coil intact
• Click and click spring functioning
• Outer anchor tight
• Correct spring installed
• Movement runs full 8‑day cycle
FAQs
Why does my mainspring slip when winding?
Usually due to a worn arbor hook or damaged inner coil.
Can a slipping click stop the clock?
Yes. A weak click allows reverse movement and power loss.
Should I replace the mainspring?
Replace it if the inner coil is cracked, stretched, or distorted.
Why does the pendulum swing weakly?
Power loss from the slipping spring affects the escapement and pendulum system.
Are New Haven 8‑day movements repairable?
Yes. Most slipping‑spring issues are fully repairable with proper service.
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