I have a Canon FTb on which all of the shutter speeds are good except for 1/8 sec. With the camera in the normal postition for shooting, it sounds like about 1/4 sec or slower. But when the camera is turned any other way (lens up, lens down, upside down) it is on. It's hard to mount it on a tripod upside down!
FYI, problem solved. I found that the front plate was cracked around the base of the lens mount on one side. This put torque on the shutter mechanism and mostly affected that one speed. So now, instead of having a mystery camera I have a parts camera.
