Learning the Citromatic Transmission: C'est Excentrique!‍

May 16, 2022

On Saturday, I was lucky enough to drive a 1971 Citroën DS 21 Pallas for the first time. If you’ve had the chance, then you may be able to relate to what I experienced, which was equal parts awesome and confounding. 

The opportunity arose when a group of us were road tripping to join a car gathering two hours away that was being hosted by Vintage Underground in Eugene, Oregon. The DS 21 is from Keith Martin’s collection, and he generously offered me the driver’s seat. We were joined by Keith’s son Bradley and good friend Ed Godshalk.

The Citroën DS 21 is famously eccentric. It is a car that started production in the mid-50s, yet still feels like it is from the future. Its defining feature is a complex hydropneumatic system that operates multiple systems, including the brakes, steering, suspension, and transmission (even power windows and directional headlights in later models!). 

It’s a technological tour de force that employs advanced methods to make simple tasks complicated and unintuitive. Case in point: Why have a brake pedal when you can have a brake button? Why not start the car by pushing the gear selector to the left? The list goes on and on….

For me, the most mystifying system to acclimate to was the DS 21’s semi-automatic transmission, called the Citromatic or BVH (Boite de Vitesses Hydraulique, or “hydraulic gearbox”). First, I’ll give you an idea of how it works, followed by a glimpse into what it’s like to drive.

Symbol of French Ingenuity

The Citroën DS 21 was the brainchild of Flaminio Bertoni, André Lefèbvre, and Paul Magès, the latter being responsible for much of the hydraulic systems’ design. The car originally appeared in 1955 and is a front-engined, front-wheel-drive car with the rear wheels pushed as far back as possible to create a spacious cabin. The model was popular from the start. During its two decades in production from 1955 to 1975, Citroën manufactured nearly 1.5 million DS 21s. 

1963 Amsterdam Auto Show (AutoRAI)

Citroën bet big on an innovative hydropneumatic system that operated the systems mentioned earlier. It combines “hydraulic” (fluid) which is not compressible, and “pneumatic” (air) which is compressible, into a single system. The system has unique properties because liquid transfers the force and the air absorbs it. This is best demonstrated by the smooth, self-leveling suspension in the DS 21, which offers a unique ride compared to springs and shock absorbers.

The liquid in the system was originally a purpose-built synthetic called LHS (Liquide Hydraulique Synthétique), which was replaced by the superior LHM (Liquide Hydraulique Minéral) which is basically mineral oil. The air is pure nitrogen.

A seven-cylinder hydraulic pump keeps the system pressurized and has two accumulators -- one for the front brakes, and a second supporting the other systems. This means the front brakes are the last to go should the system lose pressure. 

By the way, it doesn’t use a little pressure, it uses a lot. The DS 21 system operates at almost 2,500 psi -- equivalent to a gas-powered pressure washer! Don’t mess around with it unless you know what you’re doing!

Citromatic LHM Gearbox, 1973.

The Citromatic/BVH tapped into this system to create a “semi-automatic” gearbox. The gearbox is a conventional four-speed, but where it defies the norm is its use of a completely automated clutch. While there is no third pedal, the driver controls the gear shifts manually. Essentially, it’s a “flappy paddle” system that, mind you, was introduced in 1955 -- and is credited with being the first of its kind. It functions well, but for reasons only Citroën can explain, it uses a perplexing user interface to get the job done. Allow me to introduce you to “the wand.”

The Magic of the Wand

With all of the complexity of the hydropneumatic-powered clutch, the wand could not be any simpler. It is a wispy, dog-legged stalk -- looking like an extra turn signal indicator. For those who remember steering column shifters -- the proverbial “three on the tree” -- this is similar. The placement is peculiarly at noon so you have to reach over the steering wheel to manipulate it. To operate the wand takes little force and was described in brochures as "fingertip control," unlike regular gear shifters which are usually mechanically connected to the shift box.

The “shift pattern” can best be described as “C” shaped. Reverse is forward and all the way to the right. First is in the same channel as reverse, but all the way to the left. (To start the car, have it in first, then push left to crank the ignition.) Second gear is pulled toward the driver, with third and fourth positioned to the right of second in the rearward channel. Intuitive it is not. 

The part that took the most getting used to was the “time-delayed” gear changes. When shifting, one takes the foot off the pedal to ensure it doesn’t over-rev. Move the wand to select the next gear, and then count to yourself “1…2….3…4,” and then press the accelerator. It will win no drag races, and it requires some advanced planning so that the power will arrive when needed, i.e. accelerating onto an Interstate highway. 

Lastly, there is no “Park” setting. We’re conditioned when using an automatic transmission that the car is effectively in gear when not running. Not so with the Citromatic! It is in Neutral. I had to say out loud every time I parked that I was putting on the parking brake, otherwise, we may have found the car wandering away -- and potentially with a big repair bill as a result! 

Appreciating the DS 21

Despite its foibles, the Citroën DS 21 was also a revelation. The car was well ahead of its time. The long wheel-based sedan was extremely comfortable to drive and ride in. The reliance on a hydropneumatic system meant that the driving experience was more “executive” than “sporty.” The steering and brakes worked wonderfully, but since there wasn’t a mechanical connection it wasn’t as positive of a feel. Also, the self-leveling suspension kept the car flat when cornering, which took some getting used to. 

The DS 21 is a car with an overabundance of ambition. The designers were pushing the envelope, and perhaps by today’s standards, it feels a bit strange. Remember, this model is coming up at 70 years old.

The DS 21 was at its best when cruising luxuriously down the highway at 75 mph carrying four adults (and a dog!). We were relaxed and having an engaging conversation while watching the world go by through ample glass, unspoiled by beefy pillars. Not every car needs to blast around twisties, and it was a privilege to have a comfortable, civil, and social road trip that rivals even the modern cars of today.


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