75 Mack Posted October 20, 2018 Share Posted October 20, 2018 I have a 75 f model Mack that will not build pressure. When I started looking around I found a valve under the cab at the brake pedal that was leaking air and oil. Can I just replace it or is the oil a sign of a bigger problem? Also I keep reading about air dryers on brake systems but I have not been able to find one. Are they on the older trucks? Quote Link to comment Share on other sites More sharing options...
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