The 2.64 and 2.79 ratois are matched to direct drive(1:1 final ratio) transmissions. The 2.64 with direct drive is equivalent to a 3.55 with overdrive, and a 2.79 is equivalent to a 3.70 with overdrive. Some of the big companies spec these direct drive transmissions because they supposedly get a little better fuel mileage than an overdrive. This is due to having less moving parts in the tranny and thus less mechanical drag. That is the theory anyhow...I don't really know how much of a difference it would make, but any little bit helps I guess.
will a truck with 2.64 gears pull?
Discussion in 'Ask An Owner Operator' started by Evilcapitalist, Nov 3, 2008.
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Another Canadian driver Thanks this.
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Evil I PM'd you the info you will need to figure RPM's for a given set-up.Another Canadian driver Thanks this. -
Well I have a 435hp 3406E CAT with a super 10 trans and a 3.55 rear end in a '99 Freightshaker Classic XL and is currently averaging 6.72 MPG. Worst mileage so far was 6.2 MPG with 44,000lbs in the van from El Paso TX to Claycomo MO...(oh and its 1.3 million miles and counting)
just my 2 centsAnother Canadian driver Thanks this. -
And there is an operator, Randall Corlee, that pulls fuel in Oklahoma, with a Pete 389, running a C-15 Cat, tied to an 18 spd (running in direct 16th gear), hooked up to 2.64 rears, running 65-70 mph, that gets 7.5 - 8.2 avg mpg.
Another Canadian driver Thanks this. -
Another Canadian driver Thanks this.
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Another Canadian driver Thanks this.
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I put 2.74's in my Pete, went from 3.55's I have a 15 sp low reduction which has a tallish od (.79) compared to most have a .72 when I am in direct it is geared the same as it was in overdrive with the 3.55's or a little better actually at 70 I am right around 1500 rpm's in direct, the old 3.55's and overdrive at 70 I was about 1625 for rpm's. It pulls hills way better in direct then it ever did in overdrive. The only reason 2.74's work with this transmission is because of my low reduction gear to start off in when loaded. Hopefully by the end of the year I will have an 18spd in the truck, its on order right now. with an 18sp in first overdrive (17th gear is .86) I will be at around 1300-1350 at 70 which imho is perfect for fuel mileage. Right now with my current setup I am right around 6.5 mpg those are all miles loaded and empty, I still struggle and always will with vans in the wind and am around 4-5 in those situations. But even the most aero truck with proper gearing and setup struggle in North Dakota winds in the winter. I personally love the new gearing, it pulls the highway better, took awhile to get used to but once I have if you are all highway I say lower is better, my truck is now a highway princess and I don't do offroad crap with it anymore so it works for me
Another Canadian driver Thanks this. -
Drive ratio is drive ratio, it doesn't matter what the actual combination of gears are used to get there. if a 1:1 and a 2.64 is used vs a and 0.74 and 3.55, you end up with a difference of only 0.03, or 30 rpm for every 1,000. Negligible, and delivering the same torque multiplication through to the hubs (well 1800 * 2.64 vs 1800 * 2.637, so 4,752 lb-ft vs 4,728.6 lb-ft to the hubs). They will pull exactly the same, just a different means of achieving the same effect. Then add in the lower parasitic drain in a direct drive vs. overdrive, and now the trucks with 2.64 and direct drive have a fleet average of exactly 8.5 mpg (I just pulled the cumulative mpg YTD reading off the spreadsheet for all 2021-2023 models in the fleet and looked at the mean) pulling heavy reefers.
Those extra 2 mpg are huge when multiplied by 50 trucks. We're talking the difference between 17,647 gallons/year and 23,077 per truck. Those 5400 gallons of fuel savings can be used for much better things, like more driver comforts, higher paychecks, and better benefits. That's 270,000 gallons/year at 50 trucks, or a savings of over $1.2 million... or around $25,000 for the independent.
I'm sure you all could use an additional $25,000 in profit every year, right? That's why the manufacturers have come up with this formula.Another Canadian driver and Crude Truckin' Thank this. -
I pull a flatbed with a used Melton truck, isx15, 425hp, 10 speed automated with 2.64s and I can tell you for certain I don't pull mountains for ####. I don't care though let the traffic pile up behind me and I'll laugh all the way to the top at 25mph.
Another Canadian driver Thanks this.
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