Air bubbles in the LHM gives harsh ride?

jeremy · Unread post by **jeremy** » 23 Dec 2006, 23:24

Try the sit in the boot test with the engine running first - that should really confuse you.

bernie · Unread post by **bernie** » 24 Dec 2006, 10:12

There has GOT to be something we are missing????????????

steelcityuk · Unread post by **steelcityuk** » 24 Dec 2006, 11:03

Bernie, what's the cycle time on your regulator? With my Xantia the ride was good when the cycle time was long.

Steve.

steelcityuk · Unread post by **steelcityuk** » 24 Dec 2006, 15:55

If I sit in boot with engine running it rises fine as does the front.

Bled the brakes then loads of the up down stuff and release pressure from regulator bleed screw. Nice long cycles from regulator. Went for a spin around the block, very nice and smooth but by the time I'd returned home (about a mile) it was getting harsh again. Does make me wonder if doing the aerobics unsticks a valve (maybe the main HA block) which promptly sticks again under normal driving conditions. I nearly took the block to pieces too but the big brass coloured fitting was hellishly tight and I didn't want to snap it. Has anyone replaced one of these with a new one? I'm just thinking along the lines that it isn't air that's the problem but a sticky valve. This could explain why as Hydractives get older they start playing up.

Guess what I'll be stripping next.

Steve.

bernie · Unread post by **bernie** » 24 Dec 2006, 16:33

steelcityuk wrote:Bernie, what's the cycle time on your regulator? With my Xantia the ride was good when the cycle time was long.

Steve.

I'll check soon.

As to stripping the HA block, I tried on an old one but the TORX splines were starting to give on the block. Bloody tight comes to mind. So I gave up.
I'll have another go with some heat later

citronut · Unread post by **citronut** » 24 Dec 2006, 17:03

are you sure its not something like sticky hight corector linkage,so after you have been working on the car no doubt hight up and down a few times,then once back on normal hight and you have driven it it sticks back where it was before,and maybe you are getting over complicated the with you thoughts and or possabilatys to what might be the fault,try keeping it simple before getting all technical,i know this dose not acount for the H,C cycleing????
regards malcolm

bernie · Unread post by **bernie** » 24 Dec 2006, 17:12

citronut wrote:are you sure its not something like sticky hight corector linkage,so after you have been working on the car no doubt hight up and down a few times,then once back on normal hight and you have driven it it sticks back where it was before,and maybe you are getting over complicated the with you thoughts and or possabilatys to what might be the fault,try keeping it simple before getting all technical,i know this dose not acount for the H,C cycleing????
regards malcolm

Hi Malcolm, while others may be different faults, I have fitted new front and rear HC's, new f+r HA valves, new 8 spheres, new pump and new LHM and still the fault persists

steelcityuk · Unread post by **steelcityuk** » 24 Dec 2006, 17:38

I suppose that the brass coloured plug could be got out using heat and maybe even a vice. Even after stripping and cleaning it still may not work right if it's worn. I did think that it could be down to the height correctors but I must admit the front and back move up and down very smoothly. I did also think it could be the front ride height because there seems to be a large gap between the tyre and the wing but after after measuring it does sit at very near half way between min and max heights.

Bernie, have you changed the regulator on yours?

I assume that front and rear HA blocks are the same so I could just swap one for the other over the Christmas break. Maybe even throw in a strip and clean too.

Happy Christmas all!

Steve.

Mandrake · Unread post by **Mandrake** » 24 Dec 2006, 19:52

Hi Steve,

Half way between the minimum and maximum heights is not the correct ride height. (A common wrong assumption people make....)

This is because the upper and lower limit stops are different (at the front anyway) and in maximum height you have full system pressure compressing the limit stop rubber beyond where it will ever compress to with normal suspension movement.

Usually if you set the ride height by just measuring the minimum and maximum height and taking the half way point you are as much as 20-30mm too high compared to the recommended height.

See if you can find the recent thread where I posted a picture showing the ride heights and where to measure them, as this is the only way to determine the ride height correctly. (And it is fairly fussy - you want it to be within +/- 10mm from the correct height for best ride)

Edit: found the picture:

http://homepages.igrin.co.nz/simon/imag ... height.jpg

Regards,
Simon

Mandrake · Unread post by **Mandrake** » 24 Dec 2006, 20:00

bernie wrote:
citronut wrote:are you sure its not something like sticky hight corector linkage,so after you have been working on the car no doubt hight up and down a few times,then once back on normal hight and you have driven it it sticks back where it was before,and maybe you are getting over complicated the with you thoughts and or possabilatys to what might be the fault,try keeping it simple before getting all technical,i know this dose not acount for the H,C cycleing????
regards malcolm
Hi Malcolm, while others may be different faults, I have fitted new front and rear HC's, new f+r HA valves, new 8 spheres, new pump and new LHM and still the fault persists

And over the last year I've done all the spheres, stripped the pump and fitted new seals, replaced the hose from the tank to the pump, changed the LHM, stripped and cleaned both height correctors and reset the height and verified they work accurately and reliably, (no salt corrosion problems down here anyway) replaced one electrovalve and stripped/checked the other one, checked the functioning of the HA computer with an LED (no problems) replaced a worn front droplink, replaced the front struts (which were badly worn due to water entry) and although the problem is MUCH better than it originally was and occurs less often, the same basic problem is STILL there.... and the ride quality varies from excellent to p**s poor on a day to day basis seemingly at random.

Invariably any time I depressurize the suspension and change a sphere (even if its putting the same one back on) or do any other kind of work involving depressurizing the suspension, when I go for a test drive the ride is fantastic, but then deteriorates, sometimes it takes a few days, sometimes before I've even completed the test drive.

Sometimes Citrerobics restores a good ride (for a while) sometimes it doesn't. Theres no real logic behind it. Yesterday the ride was extremely good, who knows what it will be like today!

There is something pretty fundamental going wrong here, if only we could figure it out. And I'd like to point out that I've never experienced anything remotely like this problem on any other Citroen's I've owned or driven including GS's and CX's...their ride was always completely consistent - no day to day variations.

There must be something peculiar about the Xantia design (HA2 in particular) that causes it...

Regards,
Simon

bernie · Unread post by **bernie** » 24 Dec 2006, 20:21

Mandrake wrote:
The loss in damping is easy to explain - especially on a Hydractive 2 model which has long large diameter feed pipes from the struts to the centre hydractive sphere - any air mixed in with this oil is slightly compressible, which means the suspension is able to move a slight amount without oil needing to flow through the damper valves (it just compresses the air bubbles a bit) therefore small movements are not properly damped.

When there is no air the fluid is completely incompressible between the suspension ram and the damper valves, and you get very good damping of small movements, preventing oscillations.

In this case the extra compressible medium (the air/nitrogen bubbles) is on the WRONG side of the damper valve....(the nitrogen in the spheres is always on the far side of a damper valve from the struts)

The other factor to consider is that just because air is compressible doesn't mean that it being in the fluid paths between the suspension rams and the dampers/spheres is equivalent to having that much extra nitrogen in the sphere - it's not.

What you have to analyze is the pressure vs displacement curve seen by the hydraulic ram in response to suspension movement - when there is only ONE compressible medium in the circuit - the nitrogen in the sphere, you get a smooth continuous curve.

If you now introduce a second seperate compressible medium - the air bubbles, which have a VASTLY smaller volume, the situation changes.

The practical effect of this is that it feels like suspension that has badly knackered balljoints or rear arm bearings.

The dead giveaway for me is that unlike poor Bernie, whos car is like this all the time, mine only does it occassionally, just enough to remind me that there is something still wrong... and when the ride is good (most of the time now, after doing various work, including replacing the seals in the pump) its outstanding, quiet, smooth, free from harshness, brilliant.

Then every now and then the ride goes completely to hell and it starts hammering and crashing over the potholes like you wouldn't believe - sometimes in the same day that it was previously riding brilliantly!

I can't think of ANY straight mechanical problem that could cause the ride to go from brilliant to awful and back to brilliant again in the space of a day...

Regards,
Simon

PS, it seems to me that a Hydractive 2 model would be MUCH more prone to air in the oil affecting the ride than a standard model - as you have long large diameter pipes in the operating circuit to the centre sphere for air to become trapped in - pipes which are harder to flush out, compared to a standard model.

On a standard model the air would have to be in the small distance between the ram and the sphere - only a few cm's.... and air in the small feed pipe back to the height corrector probably wouldn't have much effect on abrupt bumps as the small diameter pipe would limit the flow in that direction anyway.

Has anyone noticed whether this "harsh ride" symptom is occuring more commonly with Hydractive 2 models ?

I am still of the opinion that Simon's theory is the one to track

Father Christmas will be here soon, I'll see what he reckons

bernie · Unread post by **bernie** » 24 Dec 2006, 20:25

I take it your writing this on Christmas day Simon???????

It's 8.26 pm here

Mandrake · Unread post by **Mandrake** » 24 Dec 2006, 20:39

bernie wrote: I am still of the opinion that Simon's theory is the one to track

Father Christmas will be here soon, I'll see what he reckons

Unfortunately it hasn't helped me find the problem

Oh by the way I recently checked my clear return line - and guess what, intermitant, obvious bubbling....

I came to the conclusion that maybe the piece of hose I fitted to the tank at the top wasn't sealing well after all, (the wall thickness of the hose is quite thick compared to the original and the the hose clamp may not have been making it seal) so I found my original hose and cut off the tank end of it (with the formed right angle) and refitted that with a brass joiner to the new hose about 4 inches down the side of the tank:

http://homepages.igrin.co.nz/simon/imag ... t-hose.jpg

Well that was a couple of weeks and there has been a definate improvement - still not fixed (of course) but the frequency and severity of the problem is a lot less. So this still tends to reinforce my gut feeling that air being drawn in is the root cause of the problem - but that there may not be one individual source of leakage but rather a number of small leaks that all add up.

Regards,
Simon

Mandrake · Unread post by **Mandrake** » 24 Dec 2006, 20:41

bernie wrote:I take it your writing this on Christmas day Simon???????

It's 8.26 pm here

Yes, I guess that just goes to show how obsessed we are with this problem!

It's 9:40am on Christmas Day and I'm eating breakfast, and then I'll be going to visit relatives and not thinking about cars.....(for a while)

Have a good Christmas

Regards,
Simon

steelcityuk · Unread post by **steelcityuk** » 25 Dec 2006, 00:19

Thanks for the tip Simon, I got the idea from another posting on here that half way was right. I'll check it in a few days. Makes me think that the HA blocks are the cause of all this trouble. Do HA XMs suffer too?

Steve.