I recently bought an 86 xls 2wd. The rear hard line had rusted out and the shuttle had tripped. I was also having trouble resetting it so I could bleed properly after I repaired the lines. I found it was best to actually start the motor and push the pedal with the front bleeder open, then turn the truck off. Worked great, shuttle moved easily as designed and I had no further frustration bleeding the rear correctly. It may not help if the piston is actually seized due to corrosion, but sticky shuttle seems to be a common problem. The extra boost from the engine vacuum seems to be just the thing to coax it into place. Hope this helps someone.
