There are many indicators that let you know your shocks are worn out and need to be replaced. If you notice your bike bottoming out when you hit a bump, or if you notice the rear of the bike bouncing, that means your shocks are not working like they should. If you notice oil leaking from the shock, or when you collapse the shock and it does not spring back, your shocks need replaced. Any of these indicators let you know that your shocks are worn out.