Originally Posted by S&W Rover

The picture at Smith & Wesson Barrel Stop Spring S&W SW40C SW40E SW40F SW40G SW40GP doesn't look like the right part for the SD9VE.

That picture shows a round wire spring, whereas my SD9VE (and my older SD9) have a flat spring to hold the takedown lever (or "plate") in the "up" position. The flatness may be important, because one end of the spring has to fit into the frame. Does the OP remember what the spring in your particular SD9VE looked like?

You can find a part for the Glock 19 that fits the same role. There are a number of them shown on the interweb, for sale by various vendors. Glock uses at least two variations -- one, flat; the other, round wire. You could TRY the Glock spring if you want to give that a whirl. Or, just call S&W and ask for the part...