Citroen O-Ring - Faine 385

By: Jon Faine

Presented by

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Jon Faine gets into rubber and whips his Citroen into shape

Oh for an O-ring

When the French abolished slavery in 1794 they ought to have thought a bit more carefully about the impact on the Citroen SM. Sensitive creatures it turns out, your clutch slave.

Around the same time – in the mid 1970s – when the Maserati V6 was shoehorned into a re-shaped Citroen DS envelope, creating a grand tourer to compete with the BMW CSi or the big Mercedes coupes, slavery was finally being abolished in one of the last hold-outs globally – the medieval gulf state of Oman.

Yet the engineers in Paris had no regard for human rights. Or common sense.  Or practicalities. One glance under the bonnet of an end of series 1975 semi-automatic Citroen DS kitted out with fuel injection and air conditioning demonstrates the utter abandonment of order that condemns any owner to a life of servitude. Thank goodness its big  cousin the SM only requires the mastery of the intricacies of Maserati married to the hydraulic suspension spheres of Citroen. The air conditioning is arranged at the front, the gearbox underneath and the motor under the firewall where it stays out of everyone’s way.


In almost all other cars, making the clutch engage is a simple transaction. The principle is uncomplicated. So the Citroen engineers decided to see how complex a simple clutch could be made. The adjustment of the semiautomatic – or BVH – gearbox on a DS is akin to black magic and practitioners accordingly worshipped as if members of a strange cult.

Worshipping a car is just as silly as bowing to a golden calf or any other idol. Getting an SM to run reliably though is entirely an act of faith. The manual recommends that you howl at the moon. When everything is working, it is like the Garden of Eden. When things go wrong, it is Sodom and Gomorrah.

So I find myself in gridlocked traffic, praying I get green lights all the way home. And that the starter motor does not implode.

Whipping the slave is straightforward. Sorry, whipping off the slave cylinder is straightforward enough. No legs to unshackle, just some longish bolts to undo and then some pipes to unplug. Inside, a single O-ring housed in a groove on the side of the cylinder looks serviceable but ought to be offered up as a sacrifice. The bore seems unscratched.


The piston benefits from a polish on the lathe and once I find a matching new seal we seem to be back in business. Getting the O-ring out without scratching the bore requires ceramic tipped probes manipulated dextrously along with the incantation of some choice oaths.

Making a slave bleed ought be an offence punishable by law. But after three bleeds my slave is still refusing to work. And if a slave refuses to work that un dermines the very purpose of their existence. Waiting until the stars align – and the LED torch is re-charged – allows a more intimate inspection of the pipe. A tiny tell-tale drop of green fluid dripping from the high pressure hose gives away my failing. There is apparently another O-ring required, a weeny little one, to stem the precious holy juices that make the entire machine worthy of the worship it deserves.

Such a complex, audacious innovative engineering package can all be undone for the want of a tiny rubber grommet. So once more to the altar. And with that mere rattle of a spanner 1794 becomes 1974.


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