Disc brake proportioning valve question

[70c10]

I got alot done today on my truck but ran into a snag at the end of the day I got a front end alignment done first thing in the morning and headed up to 70GMCers house to put on new rear wheel cylinders, brake shoes, and rear brake lines. We took off the rear line on the prop valve and blew compressed air thru the line to the rear and cleared out the crud!. Then when trying to bleed the rear wheel cylinder I heard a pop in the prop valve and could tell it became "uncentered" and turned the warning lamp on. We tried to clamp it with a C-clamp but it didn't work and also took it for a drive to slam on the brakes to try to recenter it but no luck. The valve has been perfect until we were bleeding the rear and it popped. Is there any other way to recenter it before I buy another valve????