Mack guy Ata Posted 2 hours ago Share Posted 2 hours ago So i own a 1956 b85 mack and there is a 1961 mack b61. My truck the b85 has a mack 9 speed and the b61 has a 20 speed quadruplex. both trucks have a I6 thermodyne. Dont know exact engine model waiting on answers from the mack museum would the 20 speed fit in to my b85 or will i need a different bell housing for the 20 speed Quote Link to comment https://www.bigmacktrucks.com/topic/76375-question-about-thermodyne-transmissions/ Share on other sites More sharing options...
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