Rock hard air suspension

[ianoliver57]

Car in question is XJ8 Sovereign 4.2 (X358) from 2009. 32K on the clock. It had a slight leak in the offside front air strut when I bought the car causing it to settle too low when parked. After pricing the genuine Jaguar replacement strut (£1450) I opted for two Aerosus comfort front struts. They were £420 each, so I could replace both struts for less than the cost of a single Jag strut. All work done by Prestige Jaguar in Paisley. Good guys. They have used these struts before with no problems.
However, since fitting, the suspension reminds me of driving my F Type! Not just potholes but every irregularity’s in road surface jarr through the car. Prestige have checked it and cannot find the cause. They have confirmed that the correct parts were ordered and supplied.
It’s been suggested that the new struts may be ‘a bit firm’ for a while being new, but really, this is more than a bit firm!
Anyone got any ideas here?

Regards

Ian.

[PaulGover]

Is the ride height correct? I replaced my front struts with the Bilstein units and had a battle to get out of "jacking" mode, where all the units remain pumped up to the maximum height, and therefore at high pressure, which would lead to a very firm ride. That also occurs if the ride height sensors fail or fall off, in which case the ECU keeps trying to pump the suspension up the the right height 'cos none if its inputs change.

If the ride height's OK, the next thing to suspect is the electronic damper controls. As I understand it, in the Bilsteins, the controls enable something inside the damper that firms them up - either a valve, or an electromagnet that interacts with the damper fluid. So perhaps your units either aren't getting the input (damaged or disconnected wiring), or are not responding correctly, and are stuck in "sports" mode. (I'm assuming you've checked the Sports mode switch on the console, of course.) That said, on my car the change in Sports mode isn't that drastic, just a reduced level of wallow in corners that I rather prefer on country roads.

I guess if checking the above two turns up nothing, you need to get back to the manufacturers to check that you have the right units and they have been correctly installed. As I understand it, there are two versions of the Bilstein struts - sports and comfort. Mine are comfort, and wallowy; I've not encountered the sports version. Perhaps Aerosus have an extra firm version.

[ianoliver57]

Hi Paul, thanks for the comments. Ride height seems ok and the struts are definitely the comfort ones as ordered and correctly supplied and fitted. Interesting point about sports mode. I thought that the sports button would only affect the gearbox, but if it alters the suspension as well, that could explain it. Could it be stuck in sports mode? For a while, before the struts were changed, pressing the sports button did nothing and I assumed it was not working. But now, if I press sports button a red light comes on on the button. Is sports mode on or off with the red light on? Got me thinking here.

Ian.

[PaulGover]

Red light is sports mode on.
On my car I'd describe the change in damping as "subtle" - it's not a choice between rock hard and wallowy, it's between wallowy and firmish. As mentioned, it makes reasonably rapid progress on windy/bumpy lanes more comfortable and secure-feeling; it doesn't say make potholes much worse.