Here is a way to make a piston on any RC car hydraulic shock valved. The valve will open one way to open all the holes in the piston and close in the opposing direction to block some of the piston holes. This allows the shock to be stiffer one way and softer the other. It is very easy to do. Lets get started!
Step 1: What you need
Your set of shocks
New shock oil (what ever weight you like to run, you may want to change the weight later after you get a feel for how this affects you RC car)
A thick plastic sandwich bag
The tools you need to take your shocks apart
Fine grain sand paper
Drill about same size as the holes in the piston (optional)