Clever LED Mod for Rear Visibility of Citroën SM

Though the Citroën SM is heralded as one of the most advanced automobiles ever manufactured, the one thing owners know all to well is that its sleek design and tapered rear end houses lights that are not all that visible to those behind.  Aside from being low the regular filament light bulbs fitted in the tail lamps are not very bright and over time dirt that collects at the rear can find it’s way behind the lenses and dull the reflectors inside the lamp assembly.  

Over the years this has resulted in a few SMs having sustained rear end collision damage.  Invariably the entire rear end and the back hatch need to be replaced.  And it’s no fun trying to get the crinkles out of the rear quarter panels and put the subtle crease back into their smooth sculpted shape. 

There is a modern LED solution from SM specialist S.A Régembeau near Lyon ( France).  Two videos showing the LEDs working are posted on YouTube.  The first one shows a a rear tail light assembly illuminating on a test bench:

And here’s a video of them actually working installed in the car:

While we can’t dissuade curious drivers from getting to close trying to wonder what the car is, this mod at least gives them a very bright indication the SM is there and what its about to do.   And it’s done without taking anything away from the original timeless design of Robert Opron.  

Régembeau, born in 1920, first got into engineering at the age of 14, when he built a tractor.  At 17 his innovative repair of a road-tarring machine (which had broken down outside his home) earned a handsome sum from a Mannheim company, which patented his modification. 

He then bought himself a Traction Avant 15/6 which modified with mechanical fuel injection, supercharging and special built six-speed gearbox.

He supercharged another four 15/6s for customers, then moved on to develop various modifications to improve the reliability of the DS.  Besides work to make the hydraulic seals more oil-tight, he devised a five-speed gearbox, greatly improving the car’s refinement and economy on the new Autoroutes.  With the DS 21 he made changes to its cylinder head and induction system, making a DS21 ie capable of attaining 138mph.

Soon Régembeau found himself infatuated with the Citroën SM and the Maserati V6 contained therein.  Originally Régembeau did diesel conversions to SM clients whose engines were giving them problems.  He had already built an 85bhp 2.0-litre four-cylinder diesel for the DS.  By the early 1970s experiments with Bosch mechanical injection and successive increases in capacity to 2.7 litres produced a reliable 180bhp – enough to push the 1450kg SM, with the four-cylinder diesel fitted, to almost 125mph.

Turning to the V6 gasoline engine in the SM, Régembeau started from the bottom end, revising the crankshaft, main bearings and piston liners, installing solid valves and redesigning the cylinder heads using better quality steel.  He also redesigned the primary timing chain with better lubrication and added automatic tensioners to this and to the secondary belt, which drives the alternator, air-con compressor and the hydraulic steering and suspension systems.

Régembeaus revisions to timing, induction and exhaust manifolds lowered peak torque from 4000rpm to a more relaxing 3000rpm, while power went up to an impressive 240bhp with triple Weber 48 carburettors. Coupled with Régembeau’s own six-speed gearbox, the Citroën SM RG could go 150 mph!  Along the way Régembeau also fitted dual superchargers in SMs taking performance to beyond even that.

Régembeau’s son Patrick gradually took over the business.  Visit:



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