Gearbox piston plan D334-26 — hydraulic fork control

In this document

The plan and its two pistons

This technical plate concerns two twin parts, referenced D334.43 ("1st and Reverse gear piston") and D334.26 ("2nd-3rd and 4th gear piston"), both designated as "Piston for hydraulic control of fork shafts" p. 18-19.

The drawing includes several views: a SECTION.A at scale 2 p. 18, a perspective view of the multi-diameter part, and an enlarged detail at scale 5 centered on a "Chamfered angle" p. 18-19.

Tolerances and specifications

A dimensioning table specifies, in relation to the reference diameter Ø1 (24), form tolerances: max run-out of 0.1 for Ø2 and Ø3, max warping of 0.2% and 0.5% for F and F1, with an explicit reference "To satisfy plans D334-45a and D334-49a" p. 18.

The dimension table at the bottom of the plate indicates, despite numerous erasures and handwritten corrections, values such as Ø1 with tolerance -0.006/-0.014 (S6), and weight and manufacturing/limit figures specific to each reference p. 18-19.

Title block and visas

The title block mentions the material "Steel C3...C4", a treatment "P...G(0.2)", the absence of coating ("none"), and refers to the "table" for the manufacturer/limit p. 18-19.

It is launched by "NOTE N° 19941" and attached to assemblies D334.08 and D334.09 p. 18-19.

The handwritten visas date the document: Guyetant (Indus.) and Cadiou (B.E.A.) on 15.3.54, Masseron (Verif) on 13.3.54, Pompon (Lab) and Caneau (M.T.) also associated with the visa p. 18-19. The filing annotation "54 to 57" appears at the top of page 18.

Context

This plan belongs to the production of the Bureau d'Études Automobiles (B.E.A.) of Citroën in the mid-1950s, a period when the engineer Paul Magès was developing the hydraulic systems that would notably equip the future DS (presented in 1955).

The "piston for hydraulic control of fork shafts" mentioned here concerns the gearbox: it is a component ensuring, by hydraulic rather than conventional mechanical means, the movement of the gear selection forks — a logic of partial automation consistent with the hydraulic control research conducted at the same time on the brand's suspensions and braking.

Archivist's perspective

This document illustrates the rigor of the industrial validation process at Citroën: five signatories (industrialization, verification, laboratory, time-methods, B.E.A.) affixed their visa a few days apart in March 1954, testifying to tight cross-checking before launch into production p. 18-19.

It seems that this plate underwent several revisions after its creation, as suggested by the numerous erasures and handwritten corrections in the dimension table — a sign of a component still being adjusted at the time of its development p. 18-19.

The handwritten mention "54 to 57" at the top of the plate suggests that this file was tracked or reclassified over several years, between 1954 and 1957. This plan probably belongs to the same documentary set as the handwritten divider "54 to 57 — Piston, clutch release cylinder", which seems to organize this same corpus of Citroën hydraulic parts from the 1950s. It can also be compared to the clutch release control piston plan D 314-12, dated the same year 1954, which follows a similar design approach within the B.E.A.