odd tire wear all of a sudden

The last set of tires wore fine. I get a new set. It's wearing fine. The shocks are very old, so I buy the gas filled Monroes for it [truck/suv (black color)]. The old shocks were dead. The ride improves and it holds the road now.

15,000 miles later, the tires start to bounce (front). I get them balanced twice. They are wearing a lot faster on the inside half, and it's starting to cup (from the bouncing). They hold the road well, and it just feels like they are going out of round. Well, they are from the cupping! On the inside!

So I check the alignment. 0" toe in. Perfect to spec. One tire has just the tiniest bit of indication of toe in in the tread wear, but probably from cornering (left tire). Inside wear indicates negative camber, so I check that. 0 degrees - perfect. I check the ball joints - tight as can be.

It rides fine, except for the increasing bounce. I rotated front to back and it started riding smooth then has bounce, cupping, and inside wear on the inside too after a couple of months.

It's an 89 4wd and I do a lot of highway driving so this is really annoying. I'm hoping this matches someone's experience and they fixed it. I've checked and done the standard checks and all seems dead on. Is the XJ sensitive to shock type and would it cause inside wear too? I don't offroad often and it's all stock and sits level. It has a firm ride, which I like, but I could change if that's the cause. The highways here are bumpy, so a fast reacting shock is good.

Thanks in advance. As I said, it all aligned fine, so I'm at a loss...

-Skip

I would check the track bar. Good luck man
Peace

What size of tires?
What pressure are you running?

235/75R15, which is the same as a '92 2wd that does fine. I try to run 32psi cold. That's what I always have run.

The old front tires, now on the back, I'm running at 36psi to run more on the center of tread rather than evenly, to avoid the cupping it got while up front. It runs a little smoother that way and one can tell it's a little over inflated at 36 by the recent wear pattern.

I have always heard that cupping was a result of bad shocksm bad alignment, or low pressure in the tire. Sounds like you have checked the alignment and the shocks. Have you tried a chalk test on the tires to see what tire pressure gives you even wear? I guess it could also be bad tires.

I really can't remember seeing cupping on the inside of the tire, to any noticeable degree on any of my XJ's. Outside edge wear and cupping are fairly common.
Check the rebound on your shocks, they should compresses then rebound very little then stop after the second (half bounce). Check your tires for out of round and take them someplace else for a balance. Preferably someplace with a bubble balancer instead of a dynamic balancer. Have them split the weights to inner and outer instead of just one side of the tire. Hint at a good tip, if the guy spends the time to do it right.
Is it possible your springs have settled? The camber isn't constant, but more of an average. The average changes as the springs settle.
I'd say loose ball joints as a guess. The only way to really test them is to get a pry bar under the tire with the front on jack stands and pry up.
In the Renix and up until around 93 or so the ball joint (bottom) seat is adjustable. It's easy to screw the bottom seat out of adjustment, tightening the bottom ball joint nut and twisting the shaft at the same time.
After making that mistake a couple of times, I super glue the bottom seat in there (just a drop or two). Heat it some with a torch to break the super glue seal if necessary next service.

Do a tire inspection: Do you off road? i.e. junk stuck around the bead., Are there any broken belts aross the ire? (had that happen before, I could only run that tire in the back and still felt a bit of shake.) Check wheels, has a woman drove it (and curbed it )

The shocks are nice and stiff on the bumper test. I did check for out of round and wobble on the front ones (current front ones) and there is none.

No off-roading on these so far (been too busy) and no women drivers. It's also affected the past front two which are now on the back, and the current two.

I did jack it up and use a bar to test the joints. I even went underneath at the same time and felt while someone lifted with a bar to feel for the slightest click or motion - none.

Is a softer shock recommended? More car-like and not lt truck/suv?