2.64 Mdrive?

Discussion in 'Mack Forum' started by rogueunh, Oct 3, 2015.

  1. rogueunh

    rogueunh Road Train Member

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    This is what they are advising on a CHU613 road tractor with the mdrive transmission. Is this common? Seems low to me, especially compared to the 13 speeds I usually have. Will this have any power on hills?
     
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  3. mp4694330

    mp4694330 Road Train Member

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  4. rogueunh

    rogueunh Road Train Member

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    Only thing I'd mention, from the Volvo site, all info is assuming 22.5. I will have 24.5.
     
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  5. mp4694330

    mp4694330 Road Train Member

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    I would find sales person who knows what they talking about, they should have software to help You choose right configuration.But that quest for him/her can be loooong.....

    Maybe this guy will help @M&KMIKE
     
    Last edited: Oct 3, 2015
  6. mountaingote

    mountaingote Road Train Member

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    You will be able to run at very low rpm on the highway, but you will be able to walk up hills faster than the truck can climb
     
  7. Cowpie1

    Cowpie1 Road Train Member

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    All you have to know is the gear ratios in the transmission, what RPM is a great balance of power and economy, and select a rear ratio that gets you in that range at the speed you will be generally running. From all I have seen, the final top gear on the mDrive is identical to the iShift in the Volvo, being they are essentially the same trans with slightly different programming. That final gear ratio is .73. Now, assuming a good RPM balance of around 1350 for the motor, that would mean a 3.21 would put you at around 65 mph at that RPM with low pro 22.5. With low pro 24.5, that would mean 3.42 would get you to 65 at 1350 RPM. You would have ample power on hills at typical 80K gross. The direct drive version of the mDrive would be different. If you ran a little faster than 65, you would not greatly hurt things. Same if you ran a little slower. 1350 is a good middle ground for doing work.

    Regarding Henry Albert's thing he has going on. I had a chat with him regarding the truck he has with the DT12 direct and 2.41 rears. When he got his record breaking cross country run grossing around 71K several months ago, he was running the DD15 between 1375 and 1425 RPM and ballpark around 65 mph, give or take. Not some goofy 1100-1200 RPM stuff that OEM's and trucking rags throw out there.

    I have never bought into the cruising at 1100 RPM stuff that goes on. Any little mole while and either downshift will occur or momentum dies quickly. Either way, not fuel efficient. The OEM's figure that the only roads anyone runs is I80/90 in Indiana or I90 in NW Illinois. Now if that is all anyone runs, or that they never have anymore than a 10K load on the trailer, maybe it might be ok.

    Now the waters get muddied a little. One can generally run in direct instead of letting the trans go into OD and get some decent results with a tall rear ratio like 2.50 or taller. Then, when you are light or running empty, let it go to OD and drop the RPM's considerably for the low RPM fuel savings. That is the general philosophy I have been using regarding using an 18 speed and 2.64 rear ratio with a Detroit 60 in my FL. I have no problem running very hilly two lane curvy roads with 45K in the box. Start off from the stop is a little slower, but at normal road speeds it is a non issue. Definitely not for local P&D type work, but a good combination for an open road truck.
     
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  8. DaveLV

    DaveLV Light Load Member

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    The rear end gear ratio is directly dependant on whether the transmission spec'd I'd direct drive or overdrive. The M-Drive and I-Shift are built identical and interchangeable, difference is software and parameter programming. If I remember right, there are about 11 different shifting programs. From economy to performance. If the salesman knows trucks he should take into account your typical haul (either local or longhaul) the area you operate (regional or cross country) the desired economy along with any other pertinent info and make a suggestion as to specs. A numerically lower rear gear would mean a direct drive trans. As has been standard for a number of years now engines operate at lower RPM's due to the emissions laws currently. They are designed with lower peak torque and HP curves. There are problems with lower operating RPM's as a lot of fleets experience incomplete regens and therefore have countless after treatment issues. FedEx especially. We have reprogrammed their ECM to drop a gear while in an automatic regent and still driving. Stationary regens are unaffected.
     
  9. savage02

    savage02 Light Load Member

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    Mack M-drive 12spd transmissions are available in 2 versions. One is a direct drive and the other is an overdrive. The overdrive model has nice ratio spreads with a final ratio of .78:1 and the direct drive is obviously a 1:1. That being said I'd be willing to bet your salesman was specing the 2.64 rear ratio to match up with the direct drive version which would be a great setup. You would have plenty of power on the hills if your running 22.5lp tires.
     
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  10. rogueunh

    rogueunh Road Train Member

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    Just got the updated specs on this, and after requesting 24.5 tall tires, they advise having a 3.25 ratio.
     
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  11. savage02

    savage02 Light Load Member

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    What kind of operation will the tractor be used in as far as weight and terrain?
     
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