Automatic Transmission Accumulators

Accumulators are shift modifiers that affect transmission shift timing and quality. They absorb the initial shock of high pressure in the apply circuit. When a clutch or band's piston or servo first strokes, the circuit has little pressure. As soon as the piston or servo bottoms and the device starts to apply, pressure increases rapidly. Without a shift modifying device like an accumulator, the device applies suddenly, and harsh shifting occurs.

Increasing throttle pressure increases the pressure on the piston's bottom, assisting the spring and providing a firmer shift. The piston strokes easily during light acceleration for a smoother, softer shift feel. During hard acceleration or wide-open throttle, throttle pressure increases, preventing the piston from stoking so easily providing a firmer shift.