Test report no. 220.769: dismantling of the rear suspension of the ELV.238 (25 April 1952)

In this document

This is test report no. 220.769 from the André Citroën Laboratory (53 rue Balard, Paris), dated 25 April 1952 p. 99, dedicated to the dismantling of the rear hydraulic suspension of the test car ELV.238 (type PVSC), following an incident that occurred during endurance testing. The mileage of the suspension examined is 19,300 km p. 99.

Incidents and consumption

No incidents were reported on the rear axle itself during these 19,300 km. However, an accumulator mounted at the end of the pump had its seals blow out several times (5,924, 18,347, 18,721 and 18,918 km), an assembly deemed "not viable" by the laboratory p. 99. Lockheed oil consumption is estimated at approximately 500 cm³ per 10,000 km, a figure presented as a simple "order of magnitude" p. 99.

Findings upon dismantling

The pressures recorded differ between the right and left sides: front accumulators 65/76 kg/cm², rear suspension spheres 31/38 kg/cm² p. 99. The right shock absorber shims are twisted and shredded, the left ones are intact. Cylinders, nylon seals and pistons are in good condition p. 99-100. A table provides the clearances measured between pistons and clamping rings:

p. 100

The connecting rods and rods on levers show traces of oxidation, with "reddened" grease p. 100. The rubber piston protectors are "worn and holed at the folds", and the distributor control fork shows wear leading to an "imprecision in the car's heights" p. 100.

The report concludes: "One of the best axles we have dismantled", while recommending that the problems with the protection of the pistons and connecting rods be resolved quickly p. 100.

Reassembly

The car was reassembled with new connecting rods with K8 ends, new rubber cylinder protectors, a cruciform axle with a cloverleaf section, and shims removed in favour of a shoulder on the shock absorber valve p. 101.

Context

In the early 1950s, Citroën was intensively developing and testing the hydropneumatic suspension designed under the direction of Paul Magès — who joined Citroën in 1925, and had drafted the plans for hydropneumatic suspension with differential interaction as early as 17 February 1944, followed by the first tests on a 2 CV in 1946 — a suspension that would notably equip the future DS, presented on 6 October 1955. These endurance tests on prototype vehicles (here designated by internal codes such as "ELV.238" or "PVSC") aimed to make the components—pistons, seals, connecting rods, accumulators—reliable before industrialisation. The André Citroën Laboratory site, rue Balard in Paris, was one of the manufacturer's test centres.

Archivist's perspective

This document illustrates the meticulous technical development work that preceded the launch of the DS: it shows, piece by piece, how engineers identified weak points (piston protection, oxidation of connecting rods, reliability of accumulators) to correct them immediately upon reassembly p. 100-101.

It seems to be part of a series of systematic endurance tests, probably one of many similar reports produced by the Citroën Laboratory during this period of intensive development. The file from which it originates can usefully be compared with the plans for hydropneumatic suspension with differential interaction, which document the design principles prior to these validation tests, as well as with the notebook of the first tests of the 2 CV with hydropneumatic suspension and the test of the 15-Six H, which mark out this same development campaign led by Paul Magès.