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Crane Truck- OD trans help


Im putting a old swinging wrecker-crane boom on a old mack. A B81, powered by soon to be turbo charged 673 its got a dual overdive quad box (going to double check) and 824 rears with 11.00 R 24 tires. (as far as i know even with the tall 24 tires its still going to be a slow truck) But the 11.00 R 24 inch rubber is getting hard to get so i might have to change the hubs and go to 11.00 R 24.5 or 12.00 R 24.5 tires. They are a smaller tire and will lower my road speed further.

What im looking for is a Dual range overdrive or a auxiliary trans that starts out at 1 to 1 and ends up with a .60 to 1 (or in that ball park). So it would be a 3 speed trans a 2 speed would be better but not sure they make something for this large of a application with that big of a jump.

Any help would be greatly appreciated.

Pete Nichols

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What about using a 13 speed overdrive , switch the 2 high gears around and make it a double overdrive .

We had a truck with 13 OD that would only run 58 mph , after turning the 2 gears around it would do 75 !!!!
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Not a bad idea, I would like to keep the factory Mack trans and just add a overdrive. But email the info Mabe I'll do this instead.
Thanks Paul


I dont know if this is any help but We had a 64 ford T850 that had a 5 speed main and 3speed aux. that was underdrive,drive and O.D. I think it was a spicer but dont remember for sure. Bob