Hard brakes at startup

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
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Brakes in 96 Rams were unique. Some early models used a vacuum pump for boost. Most models that year used hydraulic boost. If you have the vacuum pump, it may have a bad check valve which lets air leak back into the system and it takes a while for the vacuum pump to build up vacuum again. It could be also be a vacuum leak elsewhere in the system. After you shut off the engine, listen to the vacuum pump for air leaks.
If it's hydraulic boost, then I dont know. But, by the symptoms, it sounds more like a vacuum problem.
John
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The brake peddle on my 96, with vacuum pump, behaves just as "beknighted" described for his truck I have come to consider this as a characteristic of the design. Seems to me that the hard peddle at startup has been there since the truck was new. I do recall that the truck had a recall regarding a check valve. Now I got to worry about a vacuum leak?

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