This small spring helps center your shifter gates and resides under your transmissions shift tower. It especially helps when adjusting the side to side motion of the shifter inside the car.
We have noticed that over time these springs get weakened and have observed them being significantly shorter than new ones. This is a Genuine OEM Mitsubishi part and a good idea to replace if you are rebuilding your transmission. We measure this spring in each 3/S transmission we rebuild and if it is shorter than new it is replaced, but we have purchased an extra supply in case you need them for your car.