I have just dealt with the exact same problem - one of the rear shock absorbers snapped at the very top as e.g. in the photos in this post:
Renault Scenic - Rear Suspension Knock,Shock Absorbers Commonly Snapping
It must have happened while on holiday with a full load, because I didn't notice the banging noise until the first drive after I got home and unloaded the car.
I jacked up the car on the side with the banging and it was obvious the shock absorber had snapped without having to see inside the plastic protective "cup" at the top, because of the way the lower half of the shock was hanging down. I assume this plastic cup was designed as a safety fallback for when the thing snaps (it looks like they all go eventually).
Ordered a pair of KYB Gas-A-Just shock absorbers for 50 EUR including delivery plus the missing tools I needed, which of course paid for themself during this repair.
The steps I took were similar to what has been described previously in this thread.
1. Loosen wheel nuts.
2. Jack up car, remove wheel nuts and wheel.
3. Lower car onto jack stand.
4. Place jack under suspension arm and raise it up a bit. This compresses the shock absorber and makes it easier to undo the bolts. I tried it on one side without doing this and the top bolt wouldn't unscrew all the way.
5. Now comes the fun part - undo the lower bolt. This is the part that took a long time for me. At first I thought I wouldn't be able to get the nut moving at all. Eventually, after first trying to tighten the nut in order to break the bond, then trying to get it moving by hammering down on a long ratchet, I got it moving.
6. Undo top bolt using ratchet with extensions (see below) - this shouldn't be difficult.
7. Remove shock absorber (may require a bit of force to push it out at the lower end)
8. Install new shock absorber. Do the top bolt first, then cut the plastic that is compressing the shock and it will slowly expand. When the bottom part of the shock has moved down then put it in the bottom hole that it screws into. Make sure the bolts are all the way in but not tight. You want to make sure the shock absorber can still rotate, so that when you lower the car, the shock can re-angle itself to its normal operating angle.
9. Remove jack from under suspension arm. jack up car, put wheel back on, lower car, tighten wheel nuts.
10. Do the same on the other side with the other shock.
11. Bounce the car a few times.
12. Tighten the nuts to the torque specified in Haynes.
- 2x new shocks
- 1x jack
- 1x jack stand
- 1x long ratchet
- extensions for the long ratchet and torque wrench, I had to combine 25cm and 12cm extensions to undo/tighten the upper bolt (remember that it needs to be tightened with the wheel on and the car on the ground, so you need the extensions to be able to reach the upper nut from outside the wheel arch)
- 1x torque wrench
- 1x 21mm hex socket (for lower bolt)
- 1x 21mm 12-point socket (for upper bolt)
- scissors or knife
The hardest parts were:
- Removing the lower bolts, particularly on the side with the exhaust.
- Torquing the lower bolts - the problem is that the car is lowered and you've got to get under the car and tighten the bolts with not much space to work with, but I managed it.
- The shock on the "good" side i.e. the side that hadn't snapped, was only about 1cm longer uncompressed than one of the new shocks that was compressed by the plastic that needs to be cut when you unpack it. Presumably this means it was not really working effectively?
- The rear of the car is a good few cm higher than it was before, and there is visibly a few cm better clearance above the rear wheels to the top of the wheel arch.
I hope this helps some of you