The one moving/one stationary pad design of many mechanical calipers doesn't automatically make them bad. For example, the Avid BB-7 is a pretty decent mech. system with one moving piston - I had them on my MTB for years and they were great. If your son's brakes are bad, look for any of the many possible reasons for this beyond simply "one piston bad". How are the pads? Worn? Maybe a better pad compound? Rotors are clean? Compressionless, properly-routed cable housing (I found the Avids very sensitive to cable friction)? Good housing will give you much better braking. Pads correctly adjusted (the Avids have very easy-to-adjust dials on both sides - I had the stationary pad very close to the rotor, so that "rotor bending" was minimal before both pads engaged. I checked adjustment every time I removed/reinstalled a wheel, and I treated the rotors with kid gloves to ensure that they never took a hit that might warp them). Brake levers appropriate for the brakes?
What bike/brakes are these? With no disrespect, but a cheap bike with cheap brakes means that the brakes may never work particularly well. It could well be that there's nothing left but to replace the brakes, in which case dual-piston would be the way to go.
Last edited by Litespud; 08-08-22 at 01:00 PM.