Dimensioned drawing of the clutch control piston D 314-12 (Citroën, 1954)

In this document

This technical sheet is a dimensioned drawing from the Citroën design office, designating the part "PISTON DE C^DE de débrayage" (Clutch control piston), referenced D 314-12, attached to the assembly D 314.02 p. 11.

The technical drawing

The part is shown in cross-section: a cylindrical body with an interior cavity with a rounded bottom and a chamfer. Numerous dimensions and tolerances appear on the diagram: a diameter annotated "φ = 19 -0.041" (with a handwritten correction, a crossed-out digit), a spherical radius noted "3.25", an angle of "35°", an interval of "0.35 to 0.65", an angle of "120°", as well as a handwritten note "Centre ou têton prohibé" (Centre or stud prohibited) p. 11.

Material and manufacturing

The title block specifies the material: "Acier CH" (Steel CH) (a mention "C3" is crossed out), without heat treatment or specific coating ("Sans") p. 11. A weight table is also included, with FAB./LIM. values associated with numbered marks (m1, m3, m4):

Sign-offs and validation

The stakeholders table indicates a validation chain dated late July 1954: Bobelin (Draughtsman, 26-7-54), Belloncle (Verification, 26.7.54), Guyétant (Industrialisation, 29 7 54), as well as Pompon (Lab), Caneau (M.T.) and Cadiou (B.E.A.), the latter bearing a date close but partially uncertain ("29 7 57" read with uncertainty) p. 11.

The drawing also mentions that it was "LANCÉ PAR NOTE N° 20926" (Released by note No. 20926) and lists several subsequent numbered modifications (m1 to m6), with dates and note references p. 11.

Context

The clutch control piston is a classic mechanical part in automotive hydraulic clutch systems: it transmits fluid pressure to actuate the clutch, often in connection with semi-automatic or hydropneumatic systems.

At Citroën, in the mid-1950s, this research into control hydraulics was part of the broader development of technologies that would lead to the DS, presented in 1955, and its innovative hydropneumatic systems championed in particular by Paul Magès. This general context highlights the importance of such parts, although the document itself does not mention the DS.

Archivist's perspective

This D 314-12 drawing dated July 1954 seems to be part of a series of progressive developments around the hydraulic clutch system at Citroën, shortly before the commercial launch of the DS.

The handwritten note "Centre ou têton prohibé" p. 11 suggests a precise manufacturing requirement, probably related to sealing or piston guidance constraints — a concern for quality typical of precision hydraulic parts of that era.

This document finds a direct echo in the body drawing D314-11, a complementary part of the same D314.02 assembly, as well as in subsequent versions of this same piston, such as the drawing of the piston DS 314-12 from 1957, which likely testifies to an evolution or a resumption of this part after 1954.