What exactly does reversing the spring/piston on the 3-4 accumulator do?

[PaulRV6]

How and what does this affect shifting? Which is the prefered method?
thanks

 

[GNeric]

Spring against separator plate provides cushion during shift. Piston against plate and no accumulator action=harder shift. I always provide some cushion as at times, if you have aggressive enough pressure, and your converter is locked and it shifts to 4th, you can blow the back window out of the car.