Shocks fail, simple fact, either the seals go bad from age, from lack of regular service, from overheating, debris etc…
If the shock seals fail you are riding a pogo stick at best, at worst a low rider…and it needs to be fixed ASAP.
This is a quick tip to add to your memory banks if this ever happens to you, and only to be used in an emergency when there is no other option available.
What you will need is a sharp knife, a doormat (or similar heavy dense rubber), a piece of inner tube, this is optional but can make it easier and lots of duct tape.
You need to cut the rubber into sections to fit inside the gaps in your spring. The purpose of this is to create the resistance that the oil or nitrogen in your shock did before the seals failed and to reduce the pogo effect and create a little rigidity in the shock.
The inner tube may be of assistance to hold the rubber in place, then wrap the whole thing in duct tape or similar as tightly and as much as you can.
I helped this Czech guy in Eastern Russia a few years back when he had been stranded for a week and no one could help. The ‘fix’ completed!
We then remounted in his bike to get him to the nearest place that could help. Unbeknownst to me he left Eastern Russia and decided the shock felt better than stock and rode it all the way back home…his choice
He did a very good test, a crazy distance of 7500km