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'56 B-61 Rear End Ratio


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After getting my B-61LT up and running on it's maiden voyage, the highest road speed I can get out of it seems to be 52 mph. The rear end numbers are CRD78-460-29. It has the original size tires 10.00 x20 with the original TRDL-67 trans. Any suggestions on what ratio to switch to to get around 65mph at 2100 rpm, or somewhere in that area? Thanks.

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Thanks for all the great info. I will try to look for the right carrier for my original rearend. Is it probably cheaper to get a newer style rear end out of a newer Mack, with a gear ratio that is close? I know a few bone yards around my neighborhood. Is it fairly easy to swap complete rear ends or is there a lot of cobling involved to get it in there? Just asking. Thanks again.

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When you say that the 4.00 ratio is available what do you mean ? can new gears be ordered and put in an old rear end. Thanks

The 4.00 ratio was very popular in the single axle R and U models from 1965 production on. I'm not sure on gear set interchange with a older carrier. But a newer carrier should go into the older axle housing OK.


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