Hi, does anyone have experience with rear suspension? Any advise would be very very helpful.
Just today (with no issues/symptoms before) the car behaves very strange when going over bumps. I was driving and after going over a bump, I stopped because it felt like the tire is flat on the rear left (it felt like the wheel was made of wood).
There is no metallic sound. The left rear just does not compress almost at all when the trunk is pressed down (it lifts up when lifted by the bumper). The other wheels are fine.
I briefly looked but did not see any obvious havoc.
The shock were replaced probably less than 15K miles ago.

What exact model is this? A 760 with nivomat self-leveling shocks? A 740?

Sounds like you're going to need to hoist up the car, remove that rear wheel, and see what's going on.

It is 740gl 1990 sedan with regular sachs/boge touring and solid rear axle 1041-type diffential, I think.

In that case, my best guess is that one of the shock mounting bolts worked itself loose. The best thing to do - if that's the case - is remove the lower bolt, remove the shock, go get a replacement bolt, install the top bolt (to torque spec!), then jack up the body of the car so that the bolt-holes on the axle line up with the bottom of the shock.

May not have to remove the shock. I had the top bolt work out of its thread. Luckily, I was on a quiet city street when I heard something drop on to the pavement. Looked in the rearview mirror and saw an object lying on the pavement. Turned out to be that top bolt. When I got home, I supported that side on a jackstand and removed the rear wheel. With the jack I raised the hub and thus the shock until the shock's top bolt hole lined up with the body's threaded hole and reinstalled and torqued the bolt. This was on a '90 760 nivomat. There is a rubber cap that plugs into the body hole that conceals the head of the bolt. You might still have the bolt still in the shock's top bolt hole but not threaded to the bold.

For the love of Volvos,
Mike
--
'92 245DL, '90 760 GLT

Thank you good people!
I will get under the car tomorrow/on the weekend, and look for the shock asorber and bolt.

Went under the car today. There is a peep hole in the wheel well and a bolt can be seen there. Without taking the wheel off I laid under the car, grabbed the door handle with on hand and the shock absorber with the other and rocked the car up and down.
The shock absorber does seem to work - it compresses and decompresses but compresses to a point and a bump can be felt at some point as it is compressed.
The shock absorber looks different than the one on the other side of the car. On the other side, there is a metal tube coming from above going halfway over the shock. I am assuming that is part of the shock absorber, not the car.
One the problematic side the shock absorber looks just like a black cylinder. I think they are both sachs advantage.
There isn't such a tube on the problematic side. What does that mean?
I will try to draw it:

[ ] - shock problematic
[ ]
[ ]
[ ]
[ ]
[]
[ [ ] - wheel
[ [ ]
[ [ ]
[ [ ]


[[ ]] - shock working
[[ ]]
[[ ]]
[ ]
[ ]
[]
[ [ ] - wheel
[ [ ]
[ [ ]
[ [ ]

Does the 'working' side look like this?
http://www.fcpeuro.com/products/volvo-shock-absorber-rear-940-960-740-745-760-advantage

That's the way it should look. The other side.... well maybe it's time to go back to who put them on.

Yes, the working side looks like this.

Some interesting findings. The weather warmed up today. There was a water puddle under the tire. I did not think much of it as I started to take off the wheel. Once the car was up, the shock absorber was more clearly visible and looked bolted both on top and bottom.
I put the wheel back on and rocked the car. It worked fine as it did before.
It took me a few minutes to piece things together - why the shock absorber looks different, why there was a water puddle, and why it worked fine now.
The shock is put on upside down. Water is accumulated in the cylinder like thing and freezes, blocking the shock. I think so.
Unless you good people object, I will leave it as is, and wait for better weather to turn it upside down.
The shock absorber on the other side is a different brand. Buying the same brand shock and installing it on the other side would probably not make much difference as having a new and an older shock of the same brand is not that much better than two different, but probably by now balanced shocks?
Thank you for the advise!

Normally shocks are designed to be mounted with the body at the bottom and piston rod at the top. That way it takes longer for thw fluid to leak out once the rod and seal are worn. I have mounted them upside down on dirt bikes to reduce unsprung weight, but that's only good until they leak.

Clearly someone did a redneck repair with a different brand of shock mounted upside down on one side. They really should be replaced in pairs for predictable handling.
--
1992 745, >500k km

Thank you for the advice!!
I'll have the shock fliped.

I suspect on one side I have this:
https://www.eeuroparts.com/Parts/4159/Shock-Absorber-Rear-HD-1329507B/
And on the other this:
http://www.fcpeuro.com/products/volvo-shock-absorber-rear-940-960-740-745-760-advantage

There should be the same model shock on both sides, of the same age pretty much. In an emergency it's better to have working ones than not, but differences can make the car behave poorly, especially in panic situations.

I don't see much difference in the two shocks you linked to; I definitely would turn the one rightside up.
The 'cylinder like thing' is a protective cap to prevent things getting into the top of the shock body.

I wonder if the shock absorber has frozen. It got quite cold today.