DS Queer Behaviour

[pottsy]

Now some of you may recall me mentioning in a thread several months ago that my car was behaving oddly in the front suspension department.

I've just fitted newly reco-d spheres to both ends, and am somewhat bemused at a recurrence of its old habit.

It's like this. When accelerating briskly, or even gently uphill, the nose tends to rise. As it rises, the height corrector senses this and releases pressure, so the nose falls, usually fairly rapidly as one has normally backed off by now. It almost bottoms out, then realises the error of its ways and pumps up to normal height again.

It even happens at walking pace up my steepish driveway.

In the past I've replaced the return pipe (the siamesed one that takes the return from the rear height corrector as well) with one from a donor car. This return pipe definitely has the "bit of wire" inside it to slow the return process.

The height corrector seems to be acting according to Hoyle. The car rides like a DS should. I have a spare HC, that I may try on the car.

The car last exhibited this behaviour when I was running a pair of 800 psi CX spheres in the front. I replaced these with a pair of 400 psi ones and she's behaved fine until now. I put the aberrant behaviour down to the CX spheres having 2mm free-flow orifices.

Having put the correct spheres back in (presumably gassed to 860psi or thereabouts according to the book) I would have expected the beast to behave.

But not so.

Any ideas from the Brains Trust?

Pottsy

 

[DoubleChevron]

It sounds like someone has removed the fast reaction valve from the front height corrector allowing very rapid changes in height ..... Does it tend to 'overshoot' height corrections too

seeya,
Shane L.

 

[pottsy]

Shane

Didn't know it had such a thing. The only cunning bit I've found is the bit of wire stuffed into the return pipe to delay the response.

Standing on the bumper elicits the normal response after maybe 10 sec delay, same when you take the weight off, same sort of delay. No sign of overshoot as such, just that it seems to me that it shouldn't respond quite so much under acceleration.

I thought the height correctors were the same front & rear?

Is this valve of which you speak a separate bit of kit or integral with the HC?

Pottsy.

 

[DoubleChevron]

Early height correctors have a bigger port that allow the height to change rapidly, they tend to overshoot there height adjustments.

Later height correctors have a small spring and washer that blocks of a much larger sized orfice in the height corrector. This allows the car to rapidly vent pressure when required (eg: when lifting from flat or when adjusting the height). This only comes into operation where the height corrector is set to it's maximum setting.

seeya,
Shane L.

 

[Mandrake]

Are you SURE it's the front ?

It is almost certainly the REAR which is changing with the accleration, not the front.

On a front wheel drive car which has good geometry, as the DS does, the torque from the driving wheels will compress the rear suspension when you accelerate, but it will NOT alter the height of the front suspension one iota, as the front suspension is the pivot point of the torque.

The rear suspension compressing down will cause the nose of the car to rise due to pivoting about the front wheels, especially since the DS nose sticks out a long way ahead of the wheels.

Get someone else to drive the car so you can be a passenger and look out the sides and the back while they accelerate and ease off the acceleration and I'm sure you'll find its the back going up and down pivoting about the front wheel axis.

The rear height corrector attempting to correct for height changes caused by acceleration is a standard "problem" with most Hydropneumatic Citroen's, and if the suspension is soft at the rear, as it certainly would be on a DS, and you accelerate hard for 5-10 seconds at a time you will see this effect.

This includes driving up steep hills where a constant torque is being applied to climb the hill.

In a manual you don't notice it as much because when you stop accelerating during the gear change the height returns to normal momentarily and "resets" the 5 second delay of the height corrector for another 5 seconds, so the height corrector doesn't respond.

On an automatic, like my Xantia the problem is all too obvious, because the auto maintains continous acceleration long enough for the height corrector to "correct" the height.

If I accelerate quickly to 50-100Km/hr by the time I reach the desired speed and ease of the accelerator the rear suspension is bouncing off the top limit stops for a few seconds until it adjusts back down again... very annoying.

About the only thing you can do is increase the stiffness of the damping valve in the rear spheres a bit, make sure you don't gas the spheres any higher than they're supposed to be, modify your driving style a bit, or put up with it....

Regards,
Simon

 

[pottsy]

Mandrake

What you say makes perfect sense. Certainly the rears (freshly reco'd by Pleiades) seem softer that those I had in there. Fortuitously they are also early ones with the adjustable damper, so maybe that's my solution.

However.

The only fly in that ointment is that the front is definitely dropping down onto its bump stops when it happens. You can feel it!

Say Hi to Lothar for me.

Pottsy

 

[Mandrake]

Early height correctors have a bigger port that allow the height to change rapidly, they tend to overshoot there height adjustments.

Later height correctors have a small spring and washer that blocks of a much larger sized orfice in the height corrector. This allows the car to rapidly vent pressure when required (eg: when lifting from flat or when adjusting the height). This only comes into operation where the height corrector is set to it's maximum setting.

seeya,
Shane L.

Hi Shane,

What you say doesn't entirely make sense to me ? I've only overhauld "later" height correctors from GS's onwards, but what they have is a large washer on each end of the shaft in a recess with a spring under it, and between the two sides is a port with several tiny discs with tiny holes in them spaced apart from each other with brass standoffs.

In the middle of these the overflow port is connected. The delay for the height corrector moving from middle (closed) towards either end is caused by the compressing washer trying to force the oil pocket underneath it though one half of this damper valve, to the overflow pipe. From memory there are 2 - 3 discs on each side.

On the other side a vacuum pocket develops under the washer. When the height correction is made and the height corrector is moved back to centre it is able to move quickly and freely due to this vacuum pocket and when it reaches the centre it suddenly stops when the vacuum is taken up and the oil hits the washer again.

This means there is a 5 second delay for a height corrector to open, but no delay for it to close and centre itself which prevents overshooting.

Are you saying earlier height correctors don't have this ? (Interested to know as I didnt think they made any major changes to the design of them)

Regards,
Simon

 

[DoubleChevron]

Yeah,

you have described the later height correctors, the early one has no washer and spring and is what my early ID19 has on the rear.

The front however is the later type:

seeya,
Shane L.

 

[Mandrake]

Mandrake

What you say makes perfect sense. Certainly the rears (freshly reco'd by Pleiades) seem softer that those I had in there. Fortuitously they are also early ones with the adjustable damper, so maybe that's my solution.

However.

The only fly in that ointment is that the front is definitely dropping down onto its bump stops when it happens. You can feel it!

Strange.... I can't really think of anything that could be causing that.

Say Hi to Lothar for me.

Is that directed at me ? If so I don't know what you mean ?

Regards,
Simon

 

[George 1/8th]

Hey Pottsy, I'd start with the basics....make sure the LHM filters are clean, and the LHM is not too ancient.
I had no such problem when I had the DS21...but I had a similar one with the CX...which was totally fixed by replacing the safety valve....but I don't know if a DS has such a part...
Good luck....Cheers...George.

 

[pottsy]

Way back in the dim dark ages there was a comic strip entitled "Mandrake the Magician." He spent his life dressed in a dinner suit and a long flowing black cape, constantly "gesturing hynotically" and performing amazing feats.

He was accompanied by the mandatory sidekick, one Lothar. A well muscled negroid chappie always depicted in a leopard skin costume. He also performed amazing feats, but of the brute strength variety.

When I hear the name Mandrake, I automatically associate it with the old comic strip.

Mandrake was a contemporary of the Phantom (The Ghost Who Walks) and Ginger Meggs, a red-headed Sydney based Australian Larrikin always getting into trouble but saving the day as well. (How we knew he was a red-head is odd, since the comic was always drawn in B&W!)

The mind is an amazing thing, and when it's programmed in childhood, it's unlikely to be easily changed!

I guess such sophisticated culture never made it to NZ? (Believe me, you didn't miss much!)

Pottsy.

 

[pottsy]

George

I've recently flushed part of the system through. The LHM was all new about 7 months ago, but I've done a lot of work since then. I'm planning a full flush as soon as I obtain the requisite quantity of green gold!

Strangely, the rear tends to drop fairly quickly after stopping so I've been contemplating replacing the security valve anyway. This symptom, combined with the pump cycling more often than I'd like, was my rationale for replacing the brake controller. Sadly, while the cycle rate is slightly reduced, the dropping at the back time is the same so I'm looking elsewhere for causes now.

The security valve is the gadget that holds off delivering pressure to the front and rear suspension until there's sufficient pressure for the brakes/steering. A simple shuttle valve with a calibrated spring behind it.

You've got me wondering what the result of this shuttle being stuck or leaking might be. On first thought, I can't see how this would relate to the upsy downsy problem, but stranger things have happened. It is a Citroen after all!

I think a session with the hydraulic diagrams is in order for tomorrow!

Ah well, life (with a Citroen) wasn't meant to be easy!

Pottsy

 

[pottsy]

Late breaking news Dept.

Had a chat with Guru Nick from Cars of France this morning. He suggested a couple of possibles for the weird upsy downsy bit.

First was flat or soft bump stops, second was excessive free movement of the anti-roll bar. He mentioned a bronze bush or plate that can crack?

The second sounds like a possible to me, however I won't be able to suss it out for a couple of days.

Anyone care to amplify on these surmises?

Pottsy

 

[Mandrake]

He's probably refering to excessive freeplay (endfloat) in the rollbar mountings - normally there would be some bushes of some kind locating the horizontal position of the rollbar to stop it sliding left and right under load.

On a Xantia they're clamped rubber bushes (ick) on a GS they're ball shaped nylon shells, I have no idea what a DS uses, so I'll leave the experts to answer that....

Depending on how the height corrector is attached to the rollbar, freeplay in the horizontal location of the rollbar of only a few millimetres could potentially trigger large changes in height by falslely signalling the height corrector...

It's something I thought about when I was trying to track down ride height inconsistancies on my Xantia - and the way the plastic link attaches to the rollbar clamp on a Xantia means if the rollbar slid sideways at all it would throw out the height setting. As it turned out it wasn't the case in this instance.

Regards,
Simon

 

[Raybies]

I've had the same problem

When I had a D special. My wife drove it most of the time and told me the car was behaving funny and moving up and down suddenly. I didn't take much notice as when I drove it most things she complained about didn't occur. One day I was doing a U turn in busy Warrigal Rd and waiting in the turning lane and suddenly the front reared right up and then with an almighty thump it dropped down onto the suspension rubbers. I had to drive straight home for some clean undies. It was a long time ago but I dont remember spending money to get it fixed, I vaguely remember bleeding the system and I think that fixed the problem.
Good Luck and pack some spare undies in the boot.

 

[PSvensson]

Late breaking news Dept.

Had a chat with Guru Nick from Cars of France this morning. He suggested a couple of possibles for the weird upsy downsy bit.

First was flat or soft bump stops, second was excessive free movement of the anti-roll bar. He mentioned a bronze bush or plate that can crack?

The second sounds like a possible to me, however I won't be able to suss it out for a couple of days.

Anyone care to amplify on these surmises?

Pottsy

G day Potsy

have you checked if your plate has cracked?

Dan

 

[pottsy]

Today's task is to remove the mudguards and check the whole height reference system for movement, oh, and prepare a new set of Kimbies just in case!

 

[pottsy]

The Blubber needs Rubber!

Late breaking news dept, Part 2

Got the guards and covers off. Would you believe Moby is completely MISSING the lower bump stops!

I reckon this explains a hell of a lot, I just don't understand how I missed spotting their absence before! (Perhaps a Senior's Moment?)

Lacking a pair of replacements I'm going to cobble up some temporary ones from a couple of old CX rubbers I just happen to have lying around. This should at least prove the point.

More news as it comes to hand!

I'm Pottsy, and this is Whale News.

 

[JohnW]

Late breaking news dept, Part 2

Got the guards and covers off. Would you believe Moby is completely MISSING the lower bump stops!

I reckon this explains a hell of a lot, I just don't understand how I missed spotting their absence before! (Perhaps a Senior's Moment?)

Lacking a pair of replacements I'm going to cobble up some temporary ones from a couple of old CX rubbers I just happen to have lying around. This should at least prove the point.

More news as it comes to hand!

I'm Pottsy, and this is Whale News.

Following this with interest Pottsy. It's fair to assume the bump stops were missing before this errant behaviour started I presume? So they should be installed, but does this answer anything about the curious movements?

Best of luck and thanks for sharing the news.....

 

[pottsy]

The (temporary) Solution Works!

I've modified a pair of old stops from (I think) the CX I wrecked many years ago. I KNEW those bits would come in handy!

I trimmed the back of the mounts flat, drilled a hole through and temporarily attached tham to the suspension mounting bracket with a dob of Silastic and an E-Clip, or should that be an R-Clip? (See photos)

Put enough of it back together to enable a test drive and Lo & Behold, She no longer does the humpy bumpy!

WooHoo!

As far as when they went AWOL, your guess is as good as mine. Curious that I didn't even notice it gone when I was replacing the brake controller, right next to the bloody thing!

Ah well, I guess I was focussed on the job in hand.

Monday I'll place an order for a new set of rubbers both front and back.

That's the news. Now for the weather.

It's bloody hot out there! Time for a ginger beer and a metaphorical pat on the back.

Thanks all for the input. Pottsy.