Something very strange going on and I thought I'd share it to see if anyone else has come across this problem:
We're fitting new shocks to an SL350, standard shocks not ABC, and have bought the new ones from Mercs, part number 2303230800.
The new shock's pistons are not extending fully and are 100mm shorter than the original ones.
Anyone got any experience of this?

Some new suspension units have a reversing spring in them too, the new shock absorbers for the W210 are like that, they seem shorter, but the paper that comes with them mentions that they will extend to the required length when called for.

Call the dealer and ask about it.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks.
I've spoken to the dealer as well as Mercedes technical and Sachs, the manufacturer, and they can offer no advice. Sachs did tell me that it was a "captivated market part", that is that it is only available through Mercedes.
I too was beginning to wonder if there was some kind of rebound spring inside the shock and so decided to re-assemble the spring onto the strut (with some difficulty due to the short length) to see if it then extends.
The result is inconclusive at the moment because we only have one strut off the car but the newly assembled strut is still shorter than the liberated old one. Tomorrow we'll remove the other strut and do a side by side comparison.

https://www.dropbox.com/s/wo830bwssgbev13/P1030552.JPG