pre facelift vsx suspension question

deian · Post by **deian** » 31 Jan 2007, 23:19

hi all,

ok, the car in question is an M reg 1.9td VSX.

a guy at work has just bought a xantia with duff suspension, no give at all, obviously i said change the spheres and it will be a new car, naturally i check the lhm level and all was good, what i did notice though was how amazingly quick and smooth his hydractive 2 went up and down compared to mine, i was shocked.... lever was nice and loose to move, so firstly i lifted the car to check the lhm level, it went up in seconds, front and back went up at the same time, and no jerking at all. Mine is slower to move up, and usually the back goes up first. Why is this....??

Is it because most of his lhm is dumped in the sphere's so the lhm isn't working against the nitrogen.... ie nothing to push up against but the car?

or is it because he may have a different pump? (i have a 2.1 phase 2 model with hydractive 2)

or is it because of dirty fluid in my car maybe?

anyway i volunteered to change all 6 spheres on his car, there is NO give in it all, it's just passed the MOT too, not sure how it passed being so hard. he says he bangs his head on the roof often,

thanks guys

Post by **Peter.N.** » 01 Feb 2007, 00:22

No two cars seem to be the same when it comes to hydraulic pressure rise. Certainly if all the spheres were flat, as you say, the fluid doesn't have anywhere else to go so it will lift the car, but the general condition of the hydraulics has most effect, cleanness of the system, fluid and filters, leakage in height correctors, cylinders, regulator, distribution valve, brake valve, steering rack and pump, all have a role to play.

Post by **RichardW** » 01 Feb 2007, 07:42

An M reg with a single output pump will rise much faster than a later car with twin output pump - the pump output is 3 or 4 times as much. As you say flat spheres will make it rise faster as you do not have to compress the big gas pockets which takes a while with good spheres.

Mandrake · Post by **Mandrake** » 01 Feb 2007, 08:34

Yep, agree with the other posters - two things, if its a 1993 or early 1994 model with the single output pump and flow divider valve (which you can tell because there will be only ONE thick steel pipe coming out of the pump instead of the two in yours) then the effective pumping capacity for the suspension is THREE TIMES as much as the later models.

(It's about 3.3cc per revolution of the pump compared to 1cc)

So they go up in response to the lever impressively fast. (But of course they sink over night so the increased pumping capacity is offset by the fact that they lose all pressure overnight, so it still takes about the same total time to lift in the morning as an anti-sink model)

Personally I wish they'd kept the single output pump in the anti-sink models... (theres no technical reason why the anti-sink valves couldn't have been used in conjunction with a single output pump and FDV, giving a car that was ready to drive extremely quickly)

The other reason it might be fast at lifting is the gas pressure in the spheres....

Dead flat (punctured) spheres result in a fast lift from right down, because there is no gas pressure to expel the oil from the spheres when the suspension is lowered - they stay full of oil, so the only oil required is the displacement of the hydraulic ram to lift the car to the ride height.

When the spheres are gassed it takes additional oil displacement from the pump to partially fill the spheres. However when there IS gas in the spheres, the lower the gas pressure the longer it takes to lift.

(So as the spheres age it gradually takes longer and longer, and then suddenly gets quick after they puncture)

Regards,
Simon

deian · Post by **deian** » 01 Feb 2007, 14:38

i thought my theories were correct, thanks guys, interesting to know this, i think anti-sink is quite boring myself, i'd love a car that falls down overnight and lifts up in the morning!!

So any ideas on the height lever movement? his one was easy to move up and down, but mine is stiffer, and the think u pull up is quite tight to pull on the ends, i guess a dirty h/c and corrosion on the linkage?

AndersDK · Post by **AndersDK** » 01 Feb 2007, 20:41

deian wrote:... i guess a dirty h/c and corrosion on the linkage?

A really good starter I'd say 8)