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, there is little pressure in the circuit. 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 will apply to suddenly and harsh shifting would occur.
Accumulators have a valve that controls pressure. The accumulator valve is located in the valve body. It varies and regulates pressure according to demand. This pressure works with the spring on the opposite end of the accumulator piston. An increase in throttle pressure will increase the pressure on this end of the piston providing a firmer shift. During light acceleration the piston strokes easily providing a smother, softer shift feel. During hard acceleration or wide open throttle pressure is increased preventing the piston from stoking so easily providing a firmer shift.