Jaeger-LeCoultre Caliber 840 – Technical Overview from Document 1146_JLC

The Jaeger-LeCoultre Caliber 840 is a manual-winding mechanical movement introduced in the 1970s, developed as part of JLC’s ultra-thin, high-frequency watch movement lineup. According to technical document 1146_JLC, this caliber was designed for use in elegant, minimalistic timepieces, combining a sleek profile with a precise 28,800 vph escapement.

Technical Specifications

• Type: Manual-winding

• Functions: Hours, minutes (no seconds hand)

• Jewels: 17

• Frequency: 28,800 vibrations per hour (4 Hz)

• Power Reserve: Approximately 42 hours

• Diameter: ~23.3 mm

• Height: ~2.95 mm

The slimness of the movement and absence of a seconds display make Caliber 840 ideal for high-end dress watches and ultra-thin cases, especially in the brand’s formal collections of the 1970s.

Movement Architecture and Design

As shown in document 1146_JLC, Caliber 840 features:

• A high-beat balance wheel supported by a fine regulator for accurate timing

• Two-hand layout for hours and minutes, simplifying the motion works

• Compact gear train and barrel bridge, ensuring a thin, serviceable footprint

• Shock protection system on the balance assembly

The absence of a seconds hand helps reduce friction and parts wear, while also enhancing the dial’s elegance and symmetry.

Servicing Notes from 1146_JLC

• High-frequency servicing requires the use of light lubricants on escape wheel, pallet fork, and balance pivots (e.g., Moebius 9010)

• Minimal lubrication is recommended throughout due to the thin design and tight tolerances

• Target amplitude: ~270° (dial up), with beat error below 0.5 ms

• Winding gear inspection: The barrel and keyless works must be kept clean and well-oiled to ensure smooth manual winding

Assembly requires extra caution due to the low height and compact layout of the setting components.

Applications

Caliber 840 was used in:

• Ultra-thin Jaeger-LeCoultre dress watches, often in 18k gold or platinum cases

• Two-hand models, emphasizing simplicity and classic design

• LeCoultre-branded watches for the U.S. market

• Watches with flat dials, slim bezels, and minimal complications—ideal for tuxedo or formal use

Typical case sizes ranged from 32–35 mm with very low case thicknesses, often under 7 mm including the case.

Conclusion

The Jaeger-LeCoultre Caliber 840, as outlined in document 1146_JLC, exemplifies the brand’s expertise in high-precision, ultra-thin manual-winding movements. With its two-hand layout, high-frequency balance, and minimal thickness, it was perfectly suited for refined dress watches of the 1970s. Today, it remains a sought-after movement among collectors and vintage watch specialists for its blend of technical finesse and aesthetic purity.