I have a 96 2500 Cummins diesel with ABS brakes. Lately when I start it up the brake pedal will be very hard and right at the top. After a minute or so it fades down to where it is supposed to be and the brakes seem to work fine. Any idea what the problem is. could this possible be a vacuum leak? I am also gettin a little black smoke when I first start up. This usually happens first thing in the morning but sometimes after I have been driving and shut it off for several minutes or more.
Byron