I've got that sinking feeling

davehughes · Post by **davehughes** » 30 Dec 2005, 14:21

I've only had my Xantia a week. I thought that if you set the suspension to max height and switched the engine off, it would stay in the air. I set it up, went in for a coffee before starting work came back and the front had gone right down and the back was up in the air. Am I naive or is something wrong.

AndersDK · Post by **AndersDK** » 30 Dec 2005, 14:30

Nothing fancy like antisink or Hydractive on your '93 SX Xantia.
Must then be a simple front HC problem.

Note that you must never rely on a raised hydraulic suspension Citroen to do any service under the car. Always use safety jacks.

Post by **zxTd** » 30 Dec 2005, 17:37

full height is really only for "pot holes at very low speeds" and changing wheels, it does sink after a while that's normal and will stop at the standard setting, never go under the car using the suspension as a lift" it can be fatal

andmcit · Post by **andmcit** » 30 Dec 2005, 18:10

zxTd wrote:full height is really only for "pot holes at very low speeds" and changing wheels, it does sink after a while that's normal and will stop at the standard setting, never go under the car using the suspension as a lift" it can be fatal

I certainly wouldn't attack a pothole in the high setting!!

Full height is really only used when the car is stationary for changing wheels.

Otherwise use it for attacking a steep ramp or a deep flood at VERY slow [walking pace]. There is NO damping whatsover on max height so if you strike something abrupt into the wheel all that's left to absorb the energy is the strut top and rubber!!

The reason the car drops quickly from normal height is the pressure drops from the system due to ageing seals on the rams - the later post '94 cars will have the anti sink sphere to trap the pressure thus arbitrarily keeping the corner spheres in their up position. There's nothing necessarily wrong with the car though if it takes a long while to lift up the chances are the regulator is flat and the pump's having to work harder to provide the pressure into the system to get it all working.

Andrew

mezuk04 · Post by **mezuk04** » 30 Dec 2005, 18:30

Thought full height was also for off road type driving but negotiating it very slowly, as in 1st gear moving (no gas) and even 2nd gear clutch rolling.

Post by **zxTd** » 30 Dec 2005, 18:42

the uses are explained in the book

mezuk04 · Post by **mezuk04** » 30 Dec 2005, 18:43

Ah! but that involves movement and energy

Post by **zxTd** » 30 Dec 2005, 18:50

low hight is for working on engine for ease of entry/normal height is for driving/full height is for what I said, later models have sport mode and that what it does "off road" not designed for that get a 4x4

mezuk04 · Post by **mezuk04** » 30 Dec 2005, 18:53

fancy spoiling my fun

Post by **zxTd** » 30 Dec 2005, 19:00

that's life, Ive had a bad year

Mandrake · Post by **Mandrake** » 30 Dec 2005, 19:46

andmcit wrote:
zxTd wrote:full height is really only for "pot holes at very low speeds" and changing wheels, it does sink after a while that's normal and will stop at the standard setting, never go under the car using the suspension as a lift" it can be fatal
I certainly wouldn't attack a pothole in the heigh setting!!

Nor would I !!

Hitting any kind of bump at speed in the fully up (or fully down for that matter) position will place an incredible amount of strain on the strut top rubbers, and if they are close to failing, could push them over the edge...

Full height is really only used when the car is stationary for changing wheels.

Yes, or for any kind of jacking, where you don't want the suspension trying to let out its pressure while you're jacking the car up.

Otherwise use it for attacking a steep ramp or a deep flood at VERY slow [walking pace]. There is NO damping whatsover on max height so if you strike something abrupt into the wheel all that's left to absorb the energy is the strut top and rubber!!

The reason the car drops quickly from normal height is the pressure drops from the system due to ageing seals on the rams - the later post '94 cars will have the anti sink sphere to trap the pressure thus arbitrarily keeping the corner spheres in their up position. There's nothing necessarily wrong with the car though if it takes a long while to lift up the chances are the regulator is flat and the pump's having to work harder to provide the pressure into the system to get it all working.

Actually as proven by the anti-sink system, the main source of leakage is not the strut rams/cylinders. I too used to think this back when I had a GS but the anti-sink system proves beyond doubt that it is the brake doseur valve and the height correctors that are the source of 95% of the leakage that makes a Citroen go down. (With the brake doseur being up to 2 to 3 times more leaky than a height corrector, hence the reason the back tends to go down first on many models)

If you take apart a height corrector you'll see that there are NO seals on the control valve itself, the leakage is minimized purely by a very close tolerance metal to metal finish of the shaft, and any leakage occuring along this shaft finds its way into the low pressure overflow collection boots on each end and is piped back to the tank.

In fact the height corrector is deliberately designed to leak slightly like this for three reasons: to lubricate itself, also to provide the necessary oil to the hydraulic damping chambers at each end, without which it would have no delay, and finally to allow the shaft movement to be extremely low friction, and therefore sensitive to very small movements, which would not be possible if it had rubber seals on the moving shaft.

A very clever little piece of engineering the height corrector is, and it has gone basically unchanged for 45 years.

I don't know what the reason is for the rather high leakage of a brake doseur valve though, as I have never taken one apart or tried to study it closely...

The anti-sink valves isolate both the brake doseur and the height correctors from the suspension cylinders, leaving only the leakage of the suspension cylinders themselves and the anti-sink valves to allow the car to go down. In this state it can take days to fully go down, so the struts are a lot less leaky than they were originally given credit for.

Regards,
Simon

Post by **zxTd** » 30 Dec 2005, 20:22

so I can go off road in full height and rev the buckets out of it, or drop it to the floor and race it like a street rod, sorry chaps it wasnt designed for that (though it would be nice)

andmcit · Post by **andmcit** » 30 Dec 2005, 20:32

Mandrake wrote:
andmcit wrote:
zxTd wrote:full height is really only for "pot holes at very low speeds" and changing wheels, it does sink after a while that's normal and will stop at the standard setting, never go under the car using the suspension as a lift" it can be fatal
I certainly wouldn't attack a pothole in the hgh setting!!
Nor would I !!

Hitting any kind of bump at speed in the fully up (or fully down for that matter) position will place an incredible amount of strain on the strut top rubbers, and if they are close to failing, could push them over the edge...
Full height is really only used when the car is stationary for changing wheels.
Yes, or for any kind of jacking, where you don't want the suspension trying to let out its pressure while you're jacking the car up.
Otherwise use it for attacking a steep ramp or a deep flood at VERY slow [walking pace]. There is NO damping whatsover on max height so if you strike something abrupt into the wheel all that's left to absorb the energy is the strut top and rubber!!

The reason the car drops quickly from normal height is the pressure drops from the system due to ageing seals on the rams - the later post '94 cars will have the anti sink sphere to trap the pressure thus arbitrarily keeping the corner spheres in their up position. There's nothing necessarily wrong with the car though if it takes a long while to lift up the chances are the regulator is flat and the pump's having to work harder to provide the pressure into the system to get it all working.
Actually as proven by the anti-sink system, the main source of leakage is not the strut rams/cylinders. I too used to think this back when I had a GS but the anti-sink system proves beyond doubt that it is the brake doseur valve and the height correctors that are the source of 95% of the leakage that makes a Citroen go down. (With the brake doseur being up to 2 to 3 times more leaky than a height corrector, hence the reason the back tends to go down first on many models)

If you take apart a height corrector you'll see that there are NO seals on the control valve itself, the leakage is minimized purely by a very close tolerance metal to metal finish of the shaft, and any leakage occuring along this shaft finds its way into the low pressure overflow collection boots on each end and is piped back to the tank.

In fact the height corrector is deliberately designed to leak slightly like this for three reasons: to lubricate itself, also to provide the necessary oil to the hydraulic damping chambers at each end, without which it would have no delay, and finally to allow the shaft movement to be extremely low friction, and therefore sensitive to very small movements, which would not be possible if it had rubber seals on the moving shaft.

A very clever little piece of engineering the height corrector is, and it has gone basically unchanged for 45 years.

I don't know what the reason is for the rather high leakage of a brake doseur valve though, as I have never taken one apart or tried to study it closely...

The anti-sink valves isolate both the brake doseur and the height correctors from the suspension cylinders, leaving only the leakage of the suspension cylinders themselves and the anti-sink valves to allow the car to go down. In this state it can take days to fully go down, so the struts are a lot less leaky than they were originally given credit for.

Regards,
Simon

Can't say I've studied a schematic for a long while!!

Brake valve and height correctors...interesting thought!

Since driving my first Citroen - a 1220 GS [many years ago now] I've been constantly told by people who I'd expect to know better that it was the sealing on the rams!! Never had any concern to fix something that to me hasn't really been broken on any of my cars!

Thanks Simon!

The anti sink is a great novelty - a Citroen that doesn't drop to the floor over night!!

I know that my anti sink Xantia 2.0i SX has been parked untouched and has stayed UP on high for MONTHS, before it started to settle to what now looks like normal running height - this has been over ages & ages too...

All the best,
Andrew

davehughes · Post by **davehughes** » 31 Dec 2005, 09:33

It shouldn't sink within 10 minutes though should it, especially if the rear has stayed up?

AndersDK · Post by **AndersDK** » 31 Dec 2005, 09:53

davehughes wrote:It shouldn't sink within 10 minutes though should it, especially if the rear has stayed up?

No - that's why I suggest to service the front HC in my first posting.

The rest of the comments up thread are more or less on the anti-sink or hydractive system - which you do NOT have on your Xantia.