Ride is a bit bumpy but how do I know if I need shocks or if new shocks will help? Are the distances from fender to wheel center I can measure or just a bouncy test?

 

Bouncing will tell about shock condition, ride height is about spring sag and upper shock mount condition.

 

Thanks. Where do I get the ride height numbers? didn't get anything from a search.

 

from the middle of the center cap to the fender bottom - normal ride height is about 15 3/4 inches

 

A few things to go over:

1) You showed a photo of a busted nut from a new mount. If the mount was recently changed, chances are whoever did that either changed the shock, or the shock was OK
2) We all know you have low rider tires with a decent amount of tread wear. That itself would give you a harder than normal ride. Not much rubber between you and the road.
3) Tire pressure? A little bit too much could make a huge difference.

Finally, describe "Bumpy".
When you go over a series of bumps, does the car "drift", or does it recover and stay straight?

 

Shocks are NOT load bearing suspension members. Their job is to damp out spring oscillations, that's all. If your your suspension is low check for sagging springs and collapsed spring upper mounts.
Regards,

 

The lower portion of the XK8 front shock is load bearing. Therefore, lower shock bushing wear can reduce ride height slightly, but you are totally correct about shock mounts and springs.

 

HERE ARE MY NUMBERS. Now I have got new tires I can give good measurements. The fonts left and right and rear left are each 15 3/4 as I was told is norm, but the rear right is 16 1/4? A weak spring making it low I might expect but why should it be high?

 

The backs on American XK8's are typically high.


I put lowering springs on mine because it looked too jacked up for my tastes.


These is a foam spring isolator donut in back that may be more compressed on one side. Maybe a previous owner was on the heavy side.

 

You may not need new shocks but given the age of these cars now, they all need their original shock mounts replaced (front and back)....