Xantia: Soft rear suspention

Krede · Post by **Krede** » 06 Aug 2009, 16:14

I have recently begun taking on a couple of passengers on my way every morning.
With just one guy in the back seat (and he is not the biggest bloke in the world) I feel that the rear of the car drops enough to affect the steering,especially when turning.
I have noticed that when the passenger exits (the back seat) the car immediately rises again.
I had the impression that the rear hight adjuster had about 10-15 seconds delay?

I know that the rear is supposed to drop a bit under braking as the rear brakes use the pressure from the suspension... but how much should this be... on my car its quite pronounced...

I have not found these exact topic anywhere on the forum.
Any suggestions as to what the fault might be?

I have recently replaced all the spheres, and checked and adjusted the ride hight both front and rear.. I also went under the car today to check that the plastic connection to the hight corrector was in its place.
The car has done in excess of 400000km so I'm not ruling out anything.. could a brake valve be at fault ?

Old-Guy · Post by **Old-Guy** » 06 Aug 2009, 16:41

The suspension should take 10 - 15 seconds to respond to changes in load (to avoid responses to normal suspension movements) so the car should at first sink under the weight of a passenger but rise to normal within 20 seconds. Similarly the car will rise when he gets out but should sink again to the normal ride height.

When you changed the spheres, did you also:

1. Change the rear central ('anti-sink') sphere?

2. Bleed the brakes thoroughly (about ½L of LHM out of each side at the rear)?

3. Do a good session of 'Citarobics'?

Any air at all in the hydraulic system will make brakes and suspension behave strangely.

If the anti-sink sphere is in good order, when you fill up with fuel, you should notice the car gently rise as you get to about 25-30L.

Krede · Post by **Krede** » 06 Aug 2009, 16:50

Yes to all three

I noticed that the rear end didn't drop nearly as much under braking as it did before... so I'm confident that the sphere needed replacement

How soft should the rear be? .... And if the car is too soft, I take it, that would be due to too low oil pressure in the rear suspension cylinders?

Could a check be made measuring the amount of oil returned from the rear suspension?.. and which one of the hoses at the LHM tank would that be?

Old-Guy · Post by **Old-Guy** » 06 Aug 2009, 17:48

I assume you also changed the LHM and cleaned the reservoir and filters when you changed the spheres?

The constant circulation of LHM through the suspension circuits should make sure any dirt gets trapped in the filters.

The ride softness depends on the gas in the suspension spheres and the size of the holes that allow LHM in/out of the spheres. Hydraulic fluid (LHM) is not compressible so it plays no part in the suspension softness; it acts as an adjustable rigid strut between each wheel and and the gas spring in each sphere. The LHM pressure (produced by the pump) has no effect provided it is sufficient to raise the car under load.

The height control valves (slowly) adjust the volume of LHM in the struts to maintain a fixed ride height regardless of load. The control lever adjusts the 'reference points' for the height control valves.

I suggest you try a small experiment with the engine running:
- measure the height of the rear wheel arches from the road,
- get your passengers to sit in the rear seats,
the car will immediately sink under their weight, but in 20 seconds it should rise again to where it was before they sat down.

If this doesn't happen, the most likely cause is a sticking rear height control valve - give a good soak with PlusGas, leaving it to penetrate over-night, then apply aerosol 'White Grease' (as used to lubricate the door locks and hinges, bonnet latch etc.)

Krede · Post by **Krede** » 06 Aug 2009, 19:09

I assume you also changed the LHM and cleaned the reservoir and filters when you changed the spheres?

Absolutely!

I suggest you try a small experiment with the engine running:
- measure the height of the rear wheel arches from the road,
- get your passengers to sit in the rear seats,
the car will immediately sink under their weight, but in 20 seconds it should rise again to where it was before they sat down.

That was my plan too .. I'll tell both my mates to get in the back and see if it rises back up.

Krede · Post by **Krede** » 07 Aug 2009, 12:25

Did a test today... rear rises and lowers just as it is supposed to !!

Guess its just me who has to get used to the softer ride offered by the new spheres

....

I'm having the car tracked Monday... which might also help handling a bit .

Old-Guy · Post by **Old-Guy** » 08 Aug 2009, 10:17

Krede wrote: Guess its just me who has to get used to the softer ride offered by the new spheres ....

New spheres do make a huge difference if the old ones have got really bad. I hadn't realised how bad mine had got until one blew and I HAD to change them. I did all 6 when I discovered that they were all original (over 11 years and 70,000 miles or 100,000km).

Guy