I'm really liking the ride with the new lower suspension, but the rear springs would be better if they had a more firm response. If I didn't have so much horsepower due to the new engine and AVos twin screw supercharger kit, I don't think that it would be an issue.

I drive in a spirited fashion. Under WOT the rear springs need to be more rigid if I hit bumps within close range of taking off from a stop. The rear end drops really low, really quickly under WOT. The shocks are new. The car uses the CATS system.

Is it possible that I am incorrect about the spring rate and that I need to kill the CATS system for a Bilstein shock?

I drive in Sport mode with the traction turned off (traction on constantly causes the computer to pull power).

Thanks for your opinions.

 

One thing you could try if you have CATS is to unplug the controller in the rear tire well. That will put the system permenantly in "firm" mode.

Might help a little and it's free.

 

I have the Mina Rear only Springs and are happy with them. They are Progressive which provides a ride that is not as stiff (for small loadings) as other Lowering Springs. I believe that you may need a non-progressive set. They will ride a little Stiffer.

 

It has been said that Arden springs as stiffer than Mina ones. I remember this info was found from Mina website when they sold also the Arden sets.
http://shop.arden.de/jaguar/xk8/xk8-...chassis-1.html

 

Try that out, would have been my suggestion too. If you don't like it you can always plug it back in, no harm done.

 

Hopefully by next week I will know if a local supplier can set the stock CATS shocks any stiffness you preffer, stiffer ones will help here I guess.

 

Wild be interested in you findings on that. I wouldn't mind something a little firmer in sport mode, but I do like the plush option for long trips.

 

They found that the bump stops degraded after the lowering job. At low speeds, when hitting bumps, there isn't enough for the shocks to work with, so the suspension could engage the rubber bump stops. The problem didn't occur until Saturday, over a week since I had gotten the Jag back. When they put eyeballs on the workings this afternoon, they found the degraded bump stops. They ordered new ones that will be available in a few days. I remember hitting a big bump under power and that could have been what crushed the old rubber. It is quite degraded on the rear driver's side. Alan and Bill will consider the possibility of customizing the stock bump stops with extra rubber, or even make new rubber heavy duty bump stops for use in my car. It it works for my ride, they will be able to make them for others'.

 

Actually, very occasionally, over a large bump, my car also has a loud knock in the rear. Probably the Bump Stop. No sign of any contact between the tire and the wheel well.

 

did you install the rear springs for performance or to achieve a lowered look? I also want to lower the rear only, but am concerned that the ride around town will suffer.

 

They found that there was no tire contact with the inner fender, it was just the degraded rubber bump stop allowing for a clunking noise over bumps at low speed.

 

For appearance only. I chose the Mina units because they are progressive and the normal ride stiffness is not affected:

https://www.jaguarforums.com/forum/x...omplete-54377/

 

I had the new bump-stops installed by Falconworks. That solved the biggest problem. Now that the springs have settled, I am going to have the rear spring spacer added to raise the rear a small amount. That will help with WOT over bumps a bit, too.

Torn 13 year old stops:




New bump stops have an added rubber piece. We don't necessarily believe that the zip ties will actually hold for a long time, but it is fun to experiment:

 

The Mina springs have settled so much that the rear suspension is literally resting on the rear rubber bump stops.

I just now purchased a set of Adamesh springs which are reportedly the same as Arden at half the price, and, evidently, no settling like the Mina springs have exhibited. They also claim to lower the car 5 mm less. Mina and others are at a 30mm drop while the Adamesh/Arden are at 25mm of drop.

We'll see how these do.

 

One hurdle has been overcome for the re-valving of the stock CATS dampers (a refill nipple), but to reinstall the parts he needed to have an addtional tube which will be there somewhere this week. That will be that last step to be able to install new valves. So probably another week before I know more.

 

I was considering H & R lowering springs which lower the rear by 1.5" or 38mm. But according to you Jeff, even 25mm is far too much, due to springs settling over time. I was under impression that the manufacturer rated the springs with final lowering specs, but it seems that in your observation, the springs settle lower - below the manufacturer's specs. Does anyone else observe the same behavior in other aftermarket spring brands?

 

I went with the Eibach springs, they lower your car about 25mm, but I reduced it to 22mm (to accomodate my larger tires).

On the shocks: I got good news today, my shock man is confident that all can be done now, so i'll send my remaining 3 old shocks (they had about 120Kmiles on them) for refurb with stiffer setting.

Estimated price is about 170 euro per shock, but thats cheap considering you get them back in a new state (and better a little more stiffer).

It will take now at least a month or so before I have them back and can install them though.

 

My ride is really stiff which i like, as it corners really well. I asked the previous owner if it was stock because I thought the XK would be softer. He thought it was original but when I looked under earlier today I noticed it has 'KYB GAS-A-just' shocks on. Has anyone else used or heard of this make?
Greg

 

i had just order.... this: Jaguar XK8 4.0 (1998) Rear Anti-roll Bar / Rear Sway Bar / Rear Stabilizer Bar - Ultra Racing Product Catalog

 

Powerhouse in the UK is making stiffer rear bars for the X100 XK8/XKR now too 1998-2005 Jaguar XKR X100 Performance Uprated Rear Suspension Anti-Roll Sway Bar | eBay