Medium Duty Truck transmission gear ratios?

I've been shopping around for Medium Duty Trucks lately. Mostly looking at Early 2000 International 7300 and 7400s. Now my question is regarding the transmission gear ratios. Pretty much all the manual transmissions I've seen in these type of trucks have 1.00:1 as the longest gear, whether 6 speed, 7 speed or 10 speed. The (MD3060) 6 speed Allison Transmission manual says it has a 0.65:1 6th gear (I know they come locked out from the factory but I don't want this thread to turn into that discussion) but also says "Gear ratios do not include torque converter multiplication". My question is, taking into account the "torque converter multiplication" is "actual" the 6th gear of the MD3060 higher than 1:1?
 

billiebob

Well-known member
yes/no, it is overdrive at 0.65. Torque multiplication in an automatic only helps start up. Torque multiplication adds lift off the line but 0.65 is 0.65 once rolling on the interstate.

The reason/logic for 1:1 in medium, heavy trucks is 1:1, direct drive is the most efficient way to transmit power when fully loaded. And in trucks, it is all about putting the horsepower and torque to its most efficient use. 1:1, Direct goes straight, direct thru the transmissions top shaft, bypassing the power loss of gears and turning the lower shaft...... which is why heavy truck transmissions were never synchronized. The synchros also steal power.

ps the only reason for automatics today in heavy trucks is a shortage of drivers and a lack of time to train them..... the lack of clutches in light trucks is due to EPA and CAFE regulations. Todays computers can shift any vehicle at the perfect moment, delivering lower emissions and higher gas mileage than even the best most conscientious driver is capable of..... this might also be influencing the commercial driver market but ultimately in the medium/heavy truck market the issue is training drivers.

pps, generally in the medium/heavy truck market a truck with an OD transmission will also have a lower rear end ratio.
Five axle interstate trucks in the USA often have double overdrive transmissions and they fly when running under 100%.

We bought a deck truck from the USA, double overdrive 7 speed it also has a wheel lift. It can move 2 cars across state incredibly fast. I've chickened out driving it at 90mph..... I cannot imagine doing 100mph in a deck truck with a car on the deck and a car being towed. Overlanding I doubt we ever max out a medium truck. The smart way to buy a truck is to gear it for economical/efficient running at...... 60??? mph..... taking into account your final vision including GVWR and tire size.

Stock ambulances tend to be great choices cuz we often end up close to the factory ambulance weight and they tend to be geared for 70-80mph. Kind of an all around sweet spot..... unless you add larger tires effectively adding OD.... in which case a commercial transport truck geared for 65mph might be a smarter choice.
 
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yes/no, it is overdrive at 0.65. Torque multiplication in an automatic only helps start up. Torque multiplication adds lift off the line but 0.65 is 0.65 once rolling on the interstate.

The reason/logic for 1:1 in medium, heavy trucks is 1:1, direct drive is the most efficient way to transmit power when fully loaded. And in trucks, it is all about putting the horsepower and torque to its most efficient use. 1:1, Direct goes straight, direct thru the transmissions top shaft, bypassing the power loss of gears and turning the lower shaft...... which is why heavy truck transmissions were never synchronized. The synchros also steal power.

ps the only reason for automatics today in heavy trucks is a shortage of drivers and a lack of time to train them..... the lack of clutches in light trucks is due to EPA and CAFE regulations. Todays computers can shift any vehicle at the perfect moment, delivering lower emissions and higher gas mileage than even the best most conscientious driver is capable of..... this might also be influencing the commercial driver market but ultimately in the medium/heavy truck market the issue is training drivers.

pps, generally in the medium/heavy truck market a truck with an OD transmission will also have a lower rear end ratio.
Five axle interstate trucks in the USA often have double overdrive transmissions and they fly when running under 100%.

We bought a deck truck from the USA, double overdrive 7 speed it also has a wheel lift. It can move 2 cars across state incredibly fast. I've chickened out driving it at 90mph..... I cannot imagine doing 100mph in a deck truck with a car on the deck and a car being towed. Overlanding I doubt we ever max out a medium truck. The smart way to buy a truck is to gear it for economical/efficient running at...... 60??? mph..... taking into account your final vision including GVWR and tire size.

Stock ambulances tend to be great choices cuz we often end up close to the factory ambulance weight and they tend to be geared for 70-80mph. Kind of an all around sweet spot..... unless you add larger tires effectively adding OD.... in which case a commercial transport truck geared for 65mph might be a smarter choice.
I'm looking at 2 specific trucks right now, one is a 6 speed eaton (1:1 6th gear ratio) with 4.11 axle ratios, and the other is a 6 speed allison (.65:1 6th gear ratio) with 6.14 axle ratios. The rpm vs speed relationship is fairly similar between the two so which would you choose? It sounds like youd pick the manual transmission for the 1:1 trans performance?
 

Buddha.

Finally in expo white.
Does the torque converter lock up in that auto? I think that can make a big difference.
 
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