Unfortunately, even after replacing all shocks on my 99 Vanden Plas , I still don’t understand if my suspension has any kind of air assist . There were no airlines going to the shocks , yet after replacing the rear shocks ( KYB ) the rear feels a little weak !!! Is this all in my head or is there really some sort of air assist to the rear ? Please help me understand !!!

 

There is no air assist. However, the shocks are gas filled (gas under certain pressure) which works as a spring and it is combined with the action of the coil spring. If this gas leaks out, the car will sit noticeably lower.

Otherwise, KYB shocks are known to be a bit too hard. When you said "weak", did you mean the rear sits a bit lower than where it should be or the rear is bouncing when going over bumps?

 

thank you for your response . I mistakingly said that I just replaced the rear shocks with KBY shocks , however I replaced with Blistien shocks . When I press down on the front shocks they are nice and tight and they hardly travel . When I press down on the rear shocks they appear to be much looser and travel quite a bit . I replaced the shock mounts , ALL new gaskets and I’m sure they were installed correctly . If this occurred on only one side of the back shocks , I would think that I got a bad shock but both rear shocks seem too spongy . Maybe that is the way they should be on a 99 Vanden Plas . Thank you again for your input .

 

The Front suspension also has an anti-sway bar that will resist pushing down on the fender. The back of a VDP does not.

I put the stiffer Green Bilsteins in mine, instead of the blacks and I like the tightness. I have tall tires on 16" wheels, so it still rides like a pillow.

 

Like the previous poster said the black Blistien shocks are softer and that is for the soft VDP/XJ8 ride. KYBs are much stiffer and some drivers prefer to upgrade their XJs for sportiness but the tradeoff is comfort. I put KYBs all around in my XJR but switched out to green Blistiens because the KYBs were too harsh. I doubt anything is mechanically wrong with your car by the amount of work you've done, its just a matter of ride preference.