i see the zero rebound and follow the instructions to get that. My question is at that point i extend the shaft and let go and the pulls 3/4 of the way back in. So zero rebound , and at full extension the shaft pull in 3/4. Is that normal?
What you want is no force needed to push the shaft inside the cartridge fully compressed with as little air as possible doing so. Set up that way if you reach full extension the shaft will move back up, that's normal.
Once you have some (too much) rebound the car will bounce at landings and weight transfer from the rear to front will be les efficient at power. But bouncing is the main issue for me.