A retired truck mechanic told me he seen instance where the Pac brake stuck in the near closed or closed position. He thought they were poor product. I agree with him as I have had mine off twice to unseize it. I oiled it up with the Pac Brake oil after 500 miles it seized up again. At least it's seized in the open position. When it was working it was not a big help braking anyhow. It makes me wonder how many of those Pacbrakes out there are really functional. The retired mechanic opinion seems correct.