Xantia can't decide what to do with her back end

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Chlorate
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Xantia can't decide what to do with her back end

Post by Chlorate »

Hello all,
The Xant is going well, however the rear suspension appears to be doing something it shouldn't.

It seems not to be sure when to make corrections to the rear ride height, I sometimes feel the back end dropping down when I've stopped at some traffic lights, it's also very slow to drop back to normal after being hitched up to medium high.

Rear height corrector on the blink perhaps? I've read that over time they can get a bit bunged up and can get slow to respond.

Any insights greatly appreciated.

Alex
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Re: Xantia can't decide what to do with her back end

Post by citroenxm »

Quite possibly the control LINKAGES! They can get sticky spots, and when the rear drops through brake application, is moving the control lever past a sticky spot, which then of course holds the car down

They levers have spring acting connections, this is why it can stick easilly... I wouldn't of thought height corrector itself at all.. just the levers...
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Re: Xantia can't decide what to do with her back end

Post by Chlorate »

That sounds quite simple to fix, just roll about under the car with a can of brake cleaner and a tub of grease?
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Re: Xantia can't decide what to do with her back end

Post by Xaccers »

Chlorate wrote:That sounds quite simple to fix, just roll about under the car with a can of brake cleaner and a tub of grease?
With axle stands under the rear jacking points so you have plenty of safe room to work (drop the car on low so the back tilts up, switch engine off then set height to normal and it should stay tilted)
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Re: Xantia can't decide what to do with her back end

Post by Old-Guy »

As you say, sounds like sticking height correctors. It's the height corrector MECHANISM rather than the height corrector VALVE that gets stiff with age and corrosion. The rear one sits out in all the salty spray (the front one is fairly well protected at the back of the engine bay unless the engine under-tray has been removed) and suffers most.
Chlorate wrote:
That sounds quite simple to fix, just roll about under the car with a can of brake cleaner and a tub of grease?
NEVER WORK UNDERNEATH A HYDRO-PNEUMATIC CITROEN UNLESS IT IS SECURELY SUPPORTED ON AXLE STANDS, ON A LIFT OR OVER A PIT [-X

I've found that brake cleaner is completely ineffective in removing the stiff mix of dirt and old grease, and ordinary (HMP) grease is not very long-lasting. My perfect combination is spray-on Gunk with the help of a stiff glue brush to clean off the cr4p, then spray-on penetrating fluid (not WD40) to free-up the mechanism, then use brake-cleaner to get rid of the worst of the penetrating fluid, before a comprehensive dose of spray-on white grease to protect and lubricate. Heavy on the spray cans but you are working from underneath.

Ideally you take the mechanism off (no need to disturb the valve) to free it up, but it's a lot more work and not usually necessary. The alternative; on a dry day, clean off the mechanism thoroughly and soak with a good penetrating fluid, go for a drive down a rough road, do some Citaerobics, more penetrating fluid etc., and repeat until the back goes up and down smoothly, then let most of the penetrating fluid drip away before spraying with white grease (designed for locks etc. rather than fast moving parts, it's really waterproof and not easily displaced by salt spray etc). Prevention is better than cure - the height corrector (mechanism) need regular maintenance.

Pictures here to help identify the mechanism (referred to as Adjuster)
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Re: Xantia can't decide what to do with her back end

Post by Chlorate »

Old-Guy wrote:
NEVER WORK UNDERNEATH A HYDRO-PNEUMATIC CITROEN UNLESS IT IS SECURELY SUPPORTED ON AXLE STANDS, ON A LIFT OR OVER A PIT [-X
Quite, especially since I'm mucking around with the rear height corrector. Never fear, I have a good set of stands.
Hydropneumatic or not I wouldn't get under any car without it being supported properly. And besides, I wouldn't fit under it without it being jacked up :wink:

Thanks for the rest of the info, especially the pictures they're going to be very handy. I'm going to have a bash at it this weekend (weather permitting).

Alex
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Re: Xantia can't decide what to do with her back end

Post by Mandrake »

Nobody else has mentioned this, but before you expend too much effort chasing this problem I would point out that to a certain degree what you describe is perfectly normal (albeit annoying) behaviour due to the action of the rear trailing arms.

When the rear suspension moves the length of the wheel base varies due to the geometry of the trailing arms at the rear, if you have the brakes firmly applied and the car is stationary this will cause the rear suspension arms to be fairly firmly "locked" in place at the same height while the car is stationary with the foot brake applied.

If you come to a stop at traffic lights with fairly firm braking and keep the foot brake pressed firmly more often than not the rear suspension height (which is very dynamic during driving as it squats with acceleration and can either squat or lift with braking) will be either too high or too low, leading to the height corrector attempting to compensate after a few second delay. Because the foot brake is applied, initially it can't adjust the height (the arms are locked in place) but it will keep letting pressure out or putting pressure in a vain attempt to correct the height.

Either you'll let your foot off the brake to move on and the car will suddenly drop or spring up like a cork, or the difference in pressure will be enough to overcome the binding action of the brakes and the height will move anyway. (Usually with a creak/groan)

This all tends to happen a lot more with an Automatic since you're braking against the pull of the automatic gearbox, but it can happen with manuals as well. The softer the suspension the more readily this problem will occur - if the suspension is stiff due to worn spheres it won't happen at all, if its nice and soft as it should be it will tend to happen a lot depending on driving style, leading some people to think something has gone wrong after they've replaced the spheres, but unfortunately its normal.

The only real solution is to modify your driving style a bit - don't brake hard to a dead stop, ease off on the braking as you pull up to a stop so that you're just lightly applying the brakes, if its an automatic slip it into neutral just as you're rolling to a stop so that you can just apply the brakes lightly allowing the rear suspension to equalise as you stop. (Rather than having to hold the brakes on hard to hold back the pull of the idling automatic)

Or apply the handbrake once you stop and release the foot brake - this will let the rear suspension move freely and make any small correction in height required without any fuss.

You can demonstrate this locking effect of the rear arms quite easily - with the car stationary and the foot brake on firmly lift the suspension height, wait a while until you start to hear some creaking and release the brake, the rear will jump up suddenly. Put the brake on again, set the height to normal, wait a while until it creaks and let go, the back will drop like a stone.

All this is not to say that the height corrector linkage isn't in need of treatment, just don't expect it to cure this behaviour when its somewhat inherent in the suspension design.

If you can load the rear suspension down by about an inch with some load in the boot, wait 5-10 seconds and see the height correct back to the same height, remote the extra weight and see the height correct back down again in 5-10 seconds then the height corrector linkage is probably fine. (I'd still grease it as a preventative measure though)

PS slow downwards height correction of the rear suspension on Hydractive 2 Xantia's is also normal as far as I know. They're quick to rise but slow to fall, taking a lot longer to drop from maximum ride height to normal than the front suspension. There just isn't as much weight on the rear suspension to force the oil back out, and the return paths to the tank are a lot longer than the front suspension and thus have more flow resistance.

Non Hydractive 2 Xantia's fall quicker at the rear because the return path of the oil from the suspension through the height corrector to the reservoir tank does not have to pass through the additional damping valves of a hydractive regulator block, which introduce additional flow resistance on a Hydractive 2 model.
Simon

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