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)
Step 2: The concept
This is what goes on in your shock. There is oil and a piston. The oil acts as something to slow down the acceleration of the shock so the car is more stable over rough terrain. The thicker the oil or the less or smaller the holes in the piston will cause the shock to be stiffer or harder to move. The thinner the oil or the bigger or more holes will be softer or easier to move. The problem I have is that to get the extension of the shock I want (I like fast) I need to sacrifice the compression (I want a little slower)and this causes me to bottom out on jumps and causes the car to have too much “body roll” in the corners. Thats where the valve comes in. I can now tune the extension and compression of the shock separate fixing the problem I have. Now when the shock compresses, the valve will close off some of the holes in the piston making the oil go through the piston slower making the shock stiffer, but when the shock extends the valve will open which opens all the holes and allows the oil to move through the piston faster making the shock softer.