Hello guys my car unfortunately is sliding badly I changed the shocks with green billsten and new dount bushing slight improvement but still sliding at high speed I could feel the air moving the rear end of the car It was dangerous moment .
also I noticed the shocks are very soft ! The old one were stiffer I heard the green is stiffer but this one very soft if I push the car trunk down and it bounces easily
could it be the shocks? But I bought it new now what cause this ? Rear wheel bearing? Rear bushings?
Alignment is okay . Also if I reduced the tire pressure does it help?
I will take it to shop next week but I need to have idea what can cause this . 150k miles xj8 2001

 

How much psi are you running in the tires, rear specifically? Have you checked the springs, any cracks? Definitely should not be able to push the car up and down that easy. Possible defective new shocks? Unlikely but somethings definitely off here.

 

Rear subframe bushings, diff output bearings, outer pivot bearing, uj bearings, inner lca bushings, truss bushings, etc

Is there play in the wheels when it's up in the air?

 

40psi 245/45r18
I honestly can't believe both shocks are defective but the bouncing is abnormal
No cracks in springs

 

Long list
The wheel doesn't play

 

40psi seems high, at least relative to factory recommendations (34psi). Don't know if others run that high a pressure, and it probably doesn't have much to do with your weird feeling of bouncing.

"No play" eliminates about half the list. I'd personally inspect the subframe bushings (the two big ones towards the front of the rear subframe, that mount in the A-frame). Maybe try prying on them sideways with a prybar and see if the frame moves. Or you can just unbolt one of the supports to visually inspect it, if it's that trashed that it feels like your car is being blown around you'll probably be able to see it from below.
Truss bushings will be able to be easily visually/prybar inspected while under the car as well.

 

40psi is high, but probably won't cause your issues. Definitely check everything under there with a pry bar and make sure the springs are not broken. Haven't seen or heard of that on an XJ, but I've had more than one Mustang with a broken coil spring.

The bounce is certainly odd. Are the top bushings on the shocks, everything installed properly? As @nilanium said, get under there and check everything. With such an issue you're bound to find the problem rather easily.

 

Yup the shocks and the donut installed properly springs were fine .I highly believe it's the subframe bushings this or that way I'm going to order 4 bushes for the upper and another 4 bushings lower I know this car once something go wrong the other follow better change everything while there I hope there's no more parts that causes this issue
Oh the transmission also is saying goodbye 👋 it's a jaaaaaag . Funny I just changed the tensioners

Thanks for the help