Kyosho IF346-03 Big Shock Diaphragm 4pcs

A set of four diaphragms for Kyosho's Big Bore shocks.

The diaphragm is the flexible bladder that sits under the shock cap. Because oil cannot compress, something has to give as the shock shaft pushes into the body and displaces volume, and the diaphragm is that something. It flexes to absorb the displaced oil while keeping the shock sealed and, critically, keeping air out of the oil.

When a diaphragm hardens, tears or takes a permanent set, one of two things happens. Either the shock goes over-pressurised and forces the shaft back out so the suspension will not stay compressed, or it draws air in and foams the oil. Foamed oil loses damping progressively through a run without the shock ever obviously failing, so the car simply gets worse lap by lap and nothing looks broken.

That makes diaphragms one of the parts most worth replacing as routine rather than waiting for symptoms. Four are supplied, enough for a complete set of shocks. Kyosho lists them across the Inferno MP9 and MP10 families, MP9e and MP10e, MP11 and the ST-RR truggies.