C5x7 rear suspension drops to the stops - known issue?

[aerodynamica]

The car drives fine and the rear height is right until after leaving parked up for hours. It sinks down to the stops rear only and raises to normal height when started up. Seems the LDS level is OK and no oil patches underneath so I think it's an internal leak.

I'm sure I heard of a known issue for hydractive 3 that had this symptom- possibly something to do with the electrovalve having a bit of corrosion internally?

Anyone know about this?

[Kees]

A user here in the Netherlands had this problem, he replaced the BHI and the problem was over.
But, for me if I had the Choice, I leave it, because the engine like it to run stationair before start riding.
Remember, the older Citroën was this normal.
Greeting,
Kees.

[aerodynamica]

Thanks, well I'm still keen to find the old thread about it. It was possibly on the C6 forum in the past.

The problem seems to have gone away for now but I will be watching it.

[MGmike]

If it's H3+ it probably the rear firmness regulator valve sticking. It can be stripped, cleaned and rebuilt.

There's a member tutorial in the tech section of C6Owners site https://c6owners.org/download.php?view.311

[aerodynamica]

If it's H3+ it probably the rear firmness regulator valve sticking. It can be stripped, cleaned and rebuilt.

There's a member tutorial in the tech section of C6Owners site https://c6owners.org/download.php?view.311

Thank you. This is what I was looking for.

[aerodynamica]

I finally tackled the job. I attempted to unscrew the rear firmness regulator electrovalve as outlined in the C6 forum but to no avail. It would not budge and it's in horrendous condition visually.

Fortunately I had a spare firmness regulator albeit a front one. I have already removed its electrovalve to check internally so i know how tight they can be. The only visible differences on the front one I can see are the lack of bleed nipple, instead there's a metal plug that unscrewed easily. The 2x damper valves L& R have a larger centre hole and would be unsuitable for the rear suspension. I feel the C5x7 rear suspension is at times underdamped in soft mode, especially noticeable on motorways. So any reduction in damping here just wouldn't work. Plan was to swap the damper valves over and everything should be the same.

So I removed the rear regulator pictured, and after quite an effort, removed one of the damper valves. This is when the fun began... the other damper valve retained by the 30mm hex Union nut would not undo. Using the longest breaker bar - the type for crankshaft pulley, driveshaft nuts, spheres etc... it wouldn't go and eventually the 30mm hex deformed. There was no getting it out. Stumped then. But no! I have in my collection some Hydractive Xantia and XM parts including damper valves. So all was not lost. The Hydractive 2 dampers have a 1,1mm middle hole. I measure the Hydractive 3+ rear damper hole as around 1,8mm. My thoughts were to drill the 1,1 damper out to suit the C5 but I only had 1.5mm and 2.0. Obviously i went for 1,5 so the 1,1 became 1,5 and that was the solution. All reassembled and pressurised and first impressions are good. Not only does it stay up as its supposed to but the ride is better with the firmer dampers. It's still very floating in soft mode but doesn't display that underdamped tendancy now.

One unexpected thing that did cause a problem refitting the front unit to the rear was the L & R strut pipes with their 16mm Union nut wouldn't seat in the 30mm damper retaining union nut and it took me a minute to realise these are actually different internally to rear ones. The fronts are designed to take a banjo union and so have a far deeper sealing edge. I repurposed one of the rears. But of course, the other rear was the wrecked one! So what to do! The answer came in the form of a Hydractive 2 part once more. The final few years Xantia had the same pipe fitting at C5s and so the 30mm union nut is actually the same... to think I was going to scrap those parts as well.. been in my 'hydraulic bits' box for years..

Anyway, a job that should've given a day I had to squeeze into 4h so I'm glad it's gone well.

Karma though: today the steering pinion seal has begun leaking again, for the 3rd time. 2 years it lasted. Also FYI the repeated application of copper grease on the outside doesn't prevent it I have learned.

[aerodynamica]

Pictured here is the damper valves and the 30mm union nut that saved the day

[wurlycorner]

Well done getting round that problem!

[aerodynamica]

Well done getting round that problem!

Thanks Iain, it was blind luck that I had one single 30mm union nut rattling around in a bits box.

Still working well now. Only negative is that I'm not sure if the original problem was caused by a leak in the pilot valve that's operated by the solenoid or if the issue is with the slide valve that isolates the suspension sphere because both get replaced with the swapped firmness regulator. I believe it's the solenoid valve but cannot fully confirm.

[aerodynamica]

After a couple of weeks this is still working well. The suspension stays up and the ride is as good as ever.

Regarding the inconclusive cause of the internal pressure leak: I'm fairly certain the leak occurs in the electrovalve that pilots the main slide valve and not the main slide valve itself.

I've come to this conclusion because the slide valve (that moves to isolate the L&R struts from the soft suspension spheres) was found to be quite easy to move manually when I took the firmness regulator apart. Something else was likely holding it in the stiff mode position and that position can only be caused by differential fluid pressure on either end of the slide valve. The default position is SOFT suspension.

If the electrovalve activated to push the pilot valve that lets pressure out of one end of the slide valve and then causes that valve to slide and block off the L & R struts, then that's normal but the slide valve only slides back to soft when pressure is restored to the other side. A loss of sealing in the pilot valve - even after the solenoid deactivated- could see pressure leak back to the LDS tank but nothing would make the slide valve move back to soft suspension because no pressure is returned to the opposite end of the slide valve. It stays in stiff suspension. It gets stuck because in hydractive 3+ stiff (isolated) state also disconnects the raise and lower ability. The BHI unit could actually even try to lower a slightly high suspension by opening the BHI lower valve but that would only connect it to the centre soft spheres because the stuck slide valve still isolates the L & R struts. This action of the BHI to lower the height then deflates the pressure in the centre spheres without lowering the suspension that's still locked out via the slide valve in stiff mode. That's why my rear suspension seemed to be stuck in stiff mode before it dropped suddenly in traffic. This also explains the sinking of the height after the car is parked. It is physically stuck in stiff mode by the stuck slide valve and all other pressure to the centre spheres is depleted. The car is parked up, left and the various ecus turn off, including the BHI. The pressure on one side of the slide valve is minimal due to the leaking pilot valve and the pressure on the other side is the residual soft spheres pressure. The thing is locked out in stiff mode but slow pressure loss on the soft spheres side of the valve allows the spring in the slide valve to slowly push back and cause the L & R struts to slowly become reconnected to the soft spheres. This causes the suspension to drop because the pressure left in the soft spheres is less than that in the struts and so it drops. The BHI has long since turned off and no attempt is made to raise the suspension. Except next time when the car is awakened.. and it always does raise it because the internal leak is intermittent and caused by the pilot valve switching but not resealing afterwards as the solenoid activates for stiff mode.

In a nutshell: only one of the two possible moving parts could cause this because one can only move due to the other but not vice versa.

Kind of like the failure mode of one has an inevitable effect on the other. Failure of the electrovalve solenoid would leave the unit in soft mode. The BHI wouldn't care and the height could be raised & lowered regardless. Failure of the main slide valve could only be A. Seizure physically or B. Leakage. B. can't affect the height because the pressure on both ends of the valve is equal anyway. If it was A. Then it's also unlikely because the default position is in soft (fully connected) position anyway - held by a spring. And if it even was to actually seize the pressure on either end would still be equal because it was still previously all connected in its default soft state, then it would still have pressure to move back to soft mode. Unless it was REALLY seized but that was checked by inspection and the thing moved with smooth movement against the spring (that's quite stiff I found). So basically there's almost no chance the cause is the slide valve itself. There's a certain chance it's the pilot valve that vents the pressure to the lds tank and lets the like valve move. Its just the only component that can have this effect.

I'm fairly sure this is the cause.

Too bad there are so few C5s and C6s now to care