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Hi/low for mdt

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Has anyone ever thought about putting a hi low in your truck? I checked on one about 6 years ago and the way I understand is they are like a transfer case for 4x4. Say you have 4:55 gears and when you put it in high say it's 3:30 gears. I may not have my numbers exactly right. The reason I've though about it is because the mdt I'm looking at pretty much maxed out at 70 mph at 2900 rpm and I would think that would make 70 at say 1800 rpm. While empty of course. You wouldn't want it in high while pulling. But maybe while empty might jump you mpg up to 15-16 and be quieter since not as high of rpm. Not as much wear on the engine. Possibilities go up more and more.

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IMHO, you'd be better to just change the gears in the rear. If it is a "pumpkin" style rear, not that hard but heavy(!).  Go to www.roadranger.com for a chart of gear ratios, tire size, RPM's etc. You should be able to find out your engine's torque sweet spot from the mfr, aim for your most frequent top speed when you pick a ratio with that in mind.  All the 2 speed rears I've seen use an electric motor to change, many problems.

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Do your math on the torque at what rpm. If your motor don't have the torque its going to work its butt off and your mileage will be worse. My HDT (Peterbilt 359) runs 1750 rpms @ 65 mph. Sure would be nice to run around 1400 rpms. That's where my Caterpillar has the most torque (its got too much now) but it would run way quieter and maybe get better mileage. Changed a few car rear ends in my day but will pass on this one. Its got 3:90's now.

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