That service manual page shows the 490 coupler truck for 2500 cars, not the 487 for 2400 cars like the 2434 Newark. You can get access to the lock pin and spring by springing the sideframes to pop out the axle nearest the coupler and then swinging the bottom of the truck around the other axle. Push the lock pin stamping back to clear the coupler casting and lift it out, along with the spring that is on its tail end.
It is possible that your spring was damaged by overheating, probably in a derailment. When current passes through the couplers during a short circuit it can take out any of the small springs in a coupler. In that case, even if the spring is intact it will no longer be stiff, and you'll need a new spring.