driving 91 elite today.when braking lost all presure on brake peddle and left rear wheel locked up.frist time it has happened.have not touched brakes.at all. please any idea,s thanks doug.

Siezed Caliper Perhaps??

Sounds like the brakes have gone into a safety mode, they are set up so if a line is cut or split, the second circuit will still be enough to stop the car safely, when you get the pedal to the floor you are then running off the second circuit but this is pretty much a stop once in a hurry mode if that makes sense

Is not a seized caliper, I would be looking for a split or cut brake line or pipe, perhaps the master cyl has started to leak and lost fluid, best check the fluid level for starters and if any missing look for the leak

checked fluid level and for leaks strait after it happened. all looks good.going to bleed and flush the line,s today. there is plenty of pads both front and back.

thanks for your responce. turned out to be bad fluid.