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.
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.
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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