stock proportioning valve piston stuck?

[UGABRONCO]

I have a 76 with a stock proportioning valve and the brake warning light sensor. I know that there is a piston on the PV that slides to one side when there is an imbalance to prevent the complete lost of fluid. Is it possible for that piston to stick if it sits in that postion for a long time. Basically the bronco was driven without rear brakes and parked for about a year, and I have been trying to bleed the rear brakes and I cannot get any fluid to come out of the bleeder screw. Sorry for the long post, but I am so close to finishing the rear disk setup and driving the bronco again.

 

[ElJefe]

If you are converting to rear discs from drums you should replace the valve anyway. A disc/disc setup will require different front to rear proportioning than a disc/drum setup would. If your valve is original it is probably trashed anyway. I pulled apart the valve on my 76 and the insides had practically disolved from moisture in the brake fluid.