Citroen DS sphere regassing

The Citroen DS is known for the quality of its ride.   The books use epithets such as ‘Magic carpet ride’.    There is a bit of puffery in that statement, but the sentiment is right – the ride is normally very good.   Recently my DS has become the worst riding car that I own.  Something was clearly wrong.

The biggest impact on ride quality is the state of the suspension spheres.   There are four suspension spheres, one for each wheel.   In addition to the suspension spheres, a D will have at least one accumulator sphere.  These store pressure for various reasons, and my car has two, a main accumulator sphere for system pressure, and a brake accumulator sphere to provide additional pressure for the brakes should there be a leak in the system or the engine cuts out.

The spheres work by having a diaphragm with nitrogen gas under pressure in the top part of the sphere, and hydraulic oil (LHM) on the other side of the diaphragm.   The compressed gas acts as the spring.    This fails to work properly if the gas pressure is not correct.   Over a period of years, the spheres gradually loose pressure.   As long as the diaphragm is still intact, the sphere can be tested and re-gassed to the correct pressure.   Eventually the diaphragm will fail and then the sphere will no longer provide any damping.    The suspension spheres on a DS can be rebuilt with a new diaphragm if needed.

This is quite a contrast to the spheres used in the Mercedes-Benz self-leveling rear suspension, which is uses the same principal.   Those spheres are disposable, and cannot even be regassed let alone totally rebuilt.   Even worse, some people simply assume that a non-punctured diaphragm means the sphere can be re-used.   Just as in a Citroen, over time they lose pressure too.

The Citroen club have regular tech days where they offer Citroen DS sphere regassing and testing.   In the roughly ten years I’ve owned the car, I’ve removed the spheres and taken them for testing to a couple of these tech days.   Last time, they were just borderline on pressure, but the Citroen DS sphere regassing system wasn’t available, so I wasn’t able to do it.

It’s not always easy for me to make the club tech days, so I enlisted the help of my mechanic for Citroen DS sphere regassing.   He first checked the rear spheres and the news was not good.  One was totally dead, with no pressure at all.  The other had a little pressure, but negligible.  These will be sent away to be rebuilt in Queensland.

The fronts were a lot better.   They had a pressure reading of around 28, when it should have been around 60.   He was able to regas these for me without issue.   He was also able to lend me two dead spheres so at least I can move the car around the garage.     I took the car on a short drive, as I wanted to do a quick oil change before putting the car away.   I did one a few months ago, but obviously didn’t seat the oil filter gasket properly, as I had a decent oil leak from the car.  Its not possible to change the filter without draining the oil.  The driving feel was quite odd.   The front being bang on spec and the rear without any give at all.

The rear spheres should be back in a few weeks.  I anticipate them transforming the ride back to what it was when I first drove the car.   It’s one of the things that makes the DS special.