Workaround for bubbles in LHM return flow

[myglaren]

I found with my GS, BX, Xantia and even the C5s that the front always rose first, followed by the rear.

[ksanturion10]

...that's why you are driving Honda now

[myglaren]

...that's why you are driving Honda now

Not at all. Citroen parts were becoming too hard to source. The repairs to the C5 would have cost more than I paid for the Civic.
The Citroens were far superior in very many ways but of course the Citroen suspension is far, far better.
Much more room and better visibility, very comfortable seats etc.
Civic has some interesting toys but they are just a distraction mainly.

[ksanturion10]

Eh, I'm joking, really

[myglaren]

Eh, I'm joking, really

That's OK. It was clear that you were but I couldn't let go the fact that the Citroens are better by far.

[ksanturion10]

If the LHM oil has microbubbles in the hydraulic hoses and in the actuator, to do the work, it must first compress the air in the LHM and then press the diaphragm or perform work, etc. I think that on short bumps the oil moves too slowly in the tubes to compress the diaphragm which results in a rough lagged suspension response despite soft driving on a straight road. The principle of operation is the same as with air brakes. They work late and poorly!
I can't find another explanation because I tried all the advice I got and the air is still in front of the LHM pump.

The air into a closed hydraulic circuit always tends to go up, opposite to earth's gravitational force, so I don't really believe, that the pump can push it into the conjecteur tube and into the main HP circuits. It will rather escape trough the pump before reaching the conjecteur. But you are right, about the down sides of air present in hydraulic circuits, when it comes to compression.
I suggest you to take second good look at your first video -> something is not quite right over there. At first you start to push it down and it responds well by leveling at some constant distance from the tyre. After some time, while you are standing next to it (I guess you are not pushing it down at that time?), the car starts to rise its front, but the rear stays the same -> this is not correct. Generally if you are not on level ground, and if it has to rise the front, to make the body leveled, the back should fall . But I presume you are parked at leveled ground - nevertheless in both occasions for me there must be wrong height setting at the front, as James suggested earlier.

BR
Martin

Okay, maybe I should look closer , you are sitting over it and as it goes up, you jump out and it goes higher, then backs a little bit down. OK.
Can't say for sure, but still the front seems higher than usual. At that perspective, I think, while you were sitting into the engine bay, the height seemed perfect...

[ksanturion10]

Eh, I'm joking, really

That's OK. It was clear that you were but I couldn't let go the fact that the Citroens are better by far.

Hope my next and yours to be again a Citroen

[ksanturion10]

Looking at those two videos, Mat, of you pressing down on the FF and RR of the car, I would say that the suspension looks much too soft - especially for a high-BHP XM - with the body going down far too easily, and by too great an amount.

Also made me the same impression, especially at the rear. Don't know how much force you exerted there, but it looks soft.
If that is the case, other spheres + recalibration of the heights will probably solve the ride

[MatPL]

Can't say for sure, but still the front seems higher than usual. At that perspective, I think, while you were sitting into the engine bay, the height seemed perfect...

About 1 cm is higher than it should be. After exchanging the spheres, it went up and I didn't feel like regulating anymore. As soon as I pump up the multilayer, I will put them back on, then I will carry out the correction as needed. You have a good eye

[MatPL]

Looking at those two videos, Mat, of you pressing down on the FF and RR of the car, I would say that the suspension looks much too soft - especially for a high-BHP XM - with the body going down far too easily, and by too great an amount.

Also made me the same impression, especially at the rear. Don't know how much force you exerted there, but it looks soft.
If that is the case, other spheres + recalibration of the heights will probably solve the ride

I weigh about 90 kg and did not pull with all my strength. I have dedicated V6 spheres. Watch the video on page 9 May 14, 2020, 11:12. There I have IFHS 30RN corner spheres and the EV block is 375cm3 / 44 / - from the Citroen C5. For the summer I gave a smaller capacity, because I drive faster and it is more stable outside the city.

[ksanturion10]

Yeah, around 100 kg I thought you must be, but still, the speed it goes down at the rear seems fast.

Can't say for sure, but still the front seems higher than usual. At that perspective, I think, while you were sitting into the engine bay, the height seemed perfect...

About 1 cm is higher than it should be. After exchanging the spheres, it went up and I didn't feel like regulating anymore. As soon as I pump up the multilayer, I will put them back on, then I will carry out the correction as needed. You have a good eye

Generally, if I have to be honest , I have some suspicions against the adjustment procedures and the data, that circulates around the web, but that's it what it is.
But it really depends onto the diameter of the tyres at a given pressure and probably laden weight... you've said you've done it 100 times, so it won't be a mystery for you.

[white exec]

Mat,

In those last videos, which I've now watched from start to finish, the ride height is definitely wrong - too high, and by somewhat more than 1cm. The motion of the bounce test is also too easy, and too much movement for an XM.

Where long-travel strut cars like BX offer acceptable suspension behaviour (softness) with the suspension set, using the lever, to Intermediate High, the XM does not, and for a comfortable (non-nobbly) ride on XM the lever must be set to Normal height, so the suspension operates in its optimum range of movement. Moving it to Int.High hardens the ride, although I find moving it slightly in the Low direction will lower the car a little, but still retain decent softness.

It is very difficult to diagnose possible suspension faults when the car's system contains items not at standard spec, and the first step in sorting a problem is to return the car to normal settings and relevant parts.

You made some comments earlier about the lag effect of having air (microbubbles) in the hydraulic fluid. While I accept what you say about air in brake lines (making braking less positive and effective), there is a difference between brake lines and suspension lines on these cars... Brake lines are under near-zero pressure when the brakes are not applied, and any air bubbles there will significantly compress when the brakes are used, causing the familiar 'sponginess'. If the quanitity of air is large, it could allow the pedal to 'go to the floor' before any useful braking happens. We've all been there on old cars with standard braking systems.

However, on our hydraulically suspended Citroens, the suspension hydraulic lines do not operate at near-zero pressure, but are pumped up to a system pressure of around 140bar, which in turn acts on the sphere diaphragms (and rams/pistons) to raise the car to correct height, at which point the pressure feed to the spheres is switched off (height corrector) but remains high. At the correct height, the gas pressure in the spheres in considerably higher than their unloaded (refill) pressure.

The result, in a car with air in its fluid, is that when the car goes over bumps, there can be two lots of gas-compression - sphere gas and the trapped air. Both will be at the same gas pressure (they are fluid linked), but the trapped air will effectively act as "extra sphere gas volume", and will provide additional springing movement - in the same way that a larger sphere volume would.

The other, and likely main, problem is that the sphere dampers (pinhole orifice and by-pass washers) are designed to operate with fluid, and not air! If air is passing through these - and they are nowhere near gas-tight - damping will be drastically reduced, and ride quality badly compromised.

[MatPL]

In the video, the car was standing on an inclined road and maybe that's why it seems so. I set the front at about 155mm. The lower suspension selects unevenness well, but it can bounce off the stops. I set the rear at about 450mm for the same reason.
What can I do with this excessive suspension movement if the corner spheres are with the correct bore and pressure? The HA block also has the original dampers inserted. The spheres at 500cc HA blocks currently make the rocking thing worse, but not as much compared to the 450cc I had before.
Photo after firing and leveling the suspension.

[white exec]

Not sure what size tyres you have on the car, but the Citroen manual states running heights (in Normal position) as follows: (all figures are +10 -7 mm)

Front
195/70 144mm
205/60 149mm
Your setting - 155mm

Rear
195/70 431mm
205/60 436mm
Your setting - 450mm

Do you have workshop manual pages starting 430-00/1, which lists the measurement checks, and how to set them? If not, I can post these as jpg's.

The unwanted softness (car presses down too easily) is either
- sphere capacity too large
- gas pressure too high
- damping insufficient (wrong spheres, or spheres that have been drilled out, or so-called "comfort" spheres)
- centre (HA) dampers (in the regulators) fitted incorrectly, maybe

With correct spheres, dampers and height, the car (at Normal driving height) should under no driving conditions hit the bump stops. Sphere gas pressure and damping will prevent this.

What was the ride and softness like before the Xantia regulators were fitted?

[MatPL]

The unwanted softness (car presses down too easily) is either
- sphere capacity too large
- gas pressure too high
- damping insufficient (wrong spheres, or spheres that have been drilled out, or so-called "comfort" spheres)
- centre (HA) dampers (in the regulators) fitted incorrectly, maybe

The tires are 205/65/15. The tire height will be close to 195/70 and this is my starting point. The front axle is in the upper limit of the dimension, the rear axle, as I said, a little higher, because sometimes I felt that the suspension was missing when accelerating due to the low level. Soon as it should be and I will accelerate slower
You can send page 430/1. Maybe I don't have such a description yet. I am using the manual from the Polish Citroen service center on the repair and inspection of the Citroen hydraulic system.

On too soft a suspension: the larger HA ball capacity is only temporary from Saturday. I had to mount something in order to drive the car until it would fill the normal ones
- previously I used 400/64 / - on the front of the HA and on the rear axle of the HA I had 375/44 / -
- the pressure on the front multilayers is below 40
- the pressure on the rear corners of the IFHS 30RN was about 25 and I also turned it on Saturday to check / fill it up.
Before changing these spheres, it tended to over-move, and the spherical parameters were good.
- spheres do not have drilled holes
- HA dampers are mounted correctly and with the correct holes for the XM. They are even smaller than the book says (we talked about it earlier), because after measuring it was about 1.2mm.