I've been comments the past few months about the rear height of my XJS. I replaced all shocks about 6 yrs ago with KYB Gas-Adjusts. Because the "*** in the air" comments finally bugged me enough, I have researched and find it's not an optical illusion. The shocks continue to be in good shape, i.e. no bounce when pushing on bumpers. A buddy suggested the shocks are the source because they are the wrong application. He asked if coupes are heavier than convertibles. If yes, then the KYB's might be for a coupe and KYB doesn't recognize the weight difference between the two models. Imput/comments/help?

 

Convertibles are heavier.

Gas shocks can make a slight difference but what you've got goin' on there looks pretty extreme. Have the springs been changed?

Cheers
DD

 

A couple of thoughts for you. One, I don't recall the KYB's being available for the rear, I thought they were only spec'd for the front (this is from memory so I could be wrong). So that could be an issue if they aren't the right specs for the rear.

The other thought is that since the rear is a dual shock per wheel system, that will likely exaggerate any difference between the OEM shocks and the KYB's. In a single shock system, the gas shocks might not make a noticeable difference in ride hide, but becomes noticeable in a dual setup.

 

The height is determined by the springs, not the shock absorbers.

 

Not always true with gas adjustable shocks.

 

Springs are original, front is as "stiff" as the rear. Car has 210K on the clock. I talked with KYB Tech. They confirmed there is no KYB different application for coupe or convertible.

 

Right !

It takes surprisingly little force to life the car a small amount. As a demonstration, simply put your fingers under the bumper and pull upwards . You can lift the body a bit with very little exertion. And many gas shocks have high enough pressure to do exactly that.

Cheers
DD

 

Can you take a picture of the car on level ground?

 

Mine looked like this when my the subframe bushings were shot. I also made sure to use the factory shocks up front and rear.

 

92/93 XJS,

If the rear springs really are original after 29 years, it SEEMS that it's the shocks causing the issue. And in my experience, the rear springs do sag over time, hence realistically it would be even lower than normal.

As the shocks are adjustable, why not take them out to their softest settings, drive the car to settle it and see what that has done to the ride height?

Cheers

Paul

 

Here's side shots. Rear measures from ground to wheel well 1.5" higher/

 

Since you have adjustable shocks, adjust them down.

 

Sorry, people, if there's confusion. KYB Gas-Adjust shocks are not adjustable externally. It's a marketing tag to say the shocks adjust themselves by gas, assisting the hydraulic fluid.

 

The height of the lower spring perch on the shocks above the lower fixing eye is NOT the same on all makes of shock, and it is this dimension that controls the ride height even though they may be sold as being correct for the XJS rears. Over the years I have had all sorts of makes and some were hopelessly high. If you remove a shock it might be possible to lower the perch a touch somehow, with a bit of careful cutting and welding, but if not the only reliable way is to buy different ones, or better still height adjustable ones.
Measuring the perch height above the lower fixing eye will show whether a given shock will give you a different ride height - assuming the same spring is used.

 

Greg... Great info! Your tech advice is always enlightening. Even after years of being a DIY mechanic, I did not know about "the perch" detail. I'll check it. THX!

 

Thinking about it a bit more (age is wonderful isn't it) The height above the TOP fixing of the spring is also relevant! The spring, assuming the same one is used, will find the same compressed length, whatever shock is used, as the car's weight will be the same. So the ride height any given shock will give will be:
The spring compressed length plus
The distance from the bottom eye to the bottom perch, plus
The distance from the top spring fixing to the TOP eye.

So it will be necessary to measure (a) the top eye to the top fixing plus (b) the bottom eye to the bottom perch. Then adding these two together will give you a number which enables you to compare the ride height one shock absorber will give with another.

So I was half right the first time! Apologies.

 

92/93XJS,

Minor point, but in assessing the ride height, particularly in comparison to the front, don't measure from the ground to the edge of the wheelarch lip. (Particularly as the shape / height of the front and rear wheelarch lips are quite different.)

The only specific measurements that should concern you (apart from any visual assessment of the stance) are defined by Jaguar as the distance from the centre point of the wheel to the wheelarch lip (for early cars) OR the distance from the underside of the rear cage to the floor (later facelift cars). I'm not sure where the changepoint was. As yours is a facelift car, but without big bumpers, it could be one or the other? And of course, when measuring underneath, tyre size will make a difference if the car is not on original size tyres. I'll try and dig out the specified measurements if I can find them.

Cheers

Paul

 

Get those shocks out of there. Nothing else that could be done. The springs are not the issue. And check your subframe mounts for lost rubber too.

 

KYB Gas-A-just? Here is a pair of new KYB's compared to the ones I pulled off my 1989. They measured the same from the lower mount to the bottom of the spring. Measure yours and see what the length is and I will measure mine.

 

Thanks for posting that picture. It looks like the coil over seats are separate from the shock itself. Is it possible that the lower seat could be installed upside down, and therefore raise the height? Or the top and bottom seats get switched?