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.
Step 3: Take Shocks Off and Apart
Take apart your shock and drain the oil out and clean the parts. I will only show the piston for mine so I dont have to take my shocks apart again after I just rebuilt them. I will later add more detailed photos.
Step 4: Smooth the Piston
Take your piston off. Take your sand paper and smooth each face of the piston to get any extra plastic off so the valve will seal well.
Step 5: Cut Out the Valve
Place your piston on you plastic bag and mark the center of the piston with the shock shaft and cut around the piston and the hole in the middle with your exacto to get a circle of plastic with a hole in the middle. This is the valve.
Step 6: Adjusting the Valve
Put your piston back on your shock shaft then your valve on top. This way the valve closes and makes the shock stiffer when you hit a bump, land from a jump so you dont bottom out or when you take a corner so the car has less “body roll“ but still allows your suspension to extend quickly to keep you tires on the ground. Now you need to make a decision. How many holes do you want to open when the shock compresses? The more you have open the softer it will be. I would try blocking off half the holes first then go from there. When you decide cut a part of the valve off so the holes you want in action during compression are exposed. Be sure to leave some plastic around the shaft so the valve stays in place.
Step 7: Reassymble Your Shocks
Put your shock back together and fill with your choice of oil and put back on your car and try it out.
Step 8: Tips and Notes
You can drill a few more holes to adjust the amount of fluid you would like to have move through the piston up or down. I would only do this after you see how this affects you car. More holes means the piston will move faster through the shock oil.
You can try to put the valve below the piston. This will make the shock softer on compression and stiffer on extension so your car will come back to ride height slower.
You can also change your springs to a softer or stiffer spring to tune how the shock dampens. This also affects the ride height.
I just found out a few days after I wrote this Instructable, RPM Products does sell a 2 stage piston that does do this same thing. I do not know if the pistons will fit on all shocks. They recommend that you be well versed in tuning suspension before you start to play with the 2 stage or valved pistons but you can always try this and see if it is worth investing the $14 in the full set.
I went to another track a few days after this Instructable was written and tried this trick. I was bottoming out on the bigger features of the track and was also a little loose in the tight corners but liked the handeling on the rest of the track. I made some valves for the rear shocks and put the same oil that I had in the shocks and fixed my problem with out affecting what I liked. My pistons have 3 holes in them and I made the valve to close off 2 in compression.