could it be the brake light switch? its very probable the switch could be holding the pedal enough to prevent fluid getting in and letting the pedal top off.
second thing is check the parking brake to make sure its not holding the rears open just slightly, it could have the brakes out to the drums and the fluid is just pushing out the pistons in the rear enough to finish the applie.
by the way does this vehicle have rear disc or drums?
Originally Posted by Gradowski
" Treat 'em like a dog and they'll love you like a puppy!"