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I have a couple of questions someone may know the answer to. Can I put an automatic transmission in an older R model Mack with a 237 or a 300 (with a single rear axle)? Also, is it possible to put adapters on the hubs so I could put smaller wheels and tires on so it would be lower to the ground? (Say 19.5 tires) Thanks, Steelman

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Thank you for the reply. I am not familiar with the lo pro 22.5 tires. I am thinking of using an R model (or U model) to pull my 36' PJ gooseneck hydraulic dove tail trailer to take my "toys" to the shows. I was interested in using a vehicle that qualified as an antique, and since I am getting older, I wanted something that rode a little lower to the ground. Won't put that many miles on it, but figured it would last forever in that kind of situation. Several friends use 1 ton pickups, but I wanted a little more meat around me. Any thoughts, or am I barking up the wrong tree?

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you would just have to find a ratio that would provide that right road speed with the smaller tires. I'll look for sure,but I think the tire size is 255/70R22.5 There is quite a bit of height difference between those and a 11R22.5,I think they would work and would sure be alot cheaper than getting adapters and all new wheels

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you would just have to find a ratio that would provide that right road speed with the smaller tires. I'll look for sure,but I think the tire size is 255/70R22.5 There is quite a bit of height difference between those and a 11R22.5,I think they would work and would sure be alot cheaper than getting adapters and all new wheels

If it a single axle why not go to a 2 speed rear to give a "highway gear" with the automatic, it would also compensate for the smaller diameter rubber. Paul

"OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK"  Thomas Edison

 “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’

P.T.CHESHIRE

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There are no adapters that will allow you to put 19.5 wheels on in place of 22.5, the brake drums are too big to fit 19.5 rims over. As far as the automatics, most of the R models you see with a 237 or 300 have overdrive top gears. To avoid losing a lot of speed capability, you'll need a newer overdrive Allison automatic with the overdrive top gears. An Allison with the torque capacity to handle a 237 or 300 Maxidyne can be pretty spend, even if it's 15 years old.

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