264 Rear Axle Ratio???

Now if we went with a 264 ratio with a 13 direct would the 13 direct not have a lower first gear to help with startability compared to the 13 double over? This way we can take advantage of the fuel savings from running in direct at cruising speed

 

Probably, if you can actually find a 13 speed direct nowadays. I know of no currently produced 13 speed direct drive top gear. 11th in a typical 13 is direct. If not typically running real heavy, a 13 in front of 2.64 would work just fine. The basement gears are low enough to get the job done. Might not be the best choice is doing a lot of hill starts with full gross. That is where the 18 comes in handy. Under many situations, I use my 18 similar to a 13 shift pattern. Only in the extreme situations do I need the low end of an 18 speed.

A 13 is not going to provide the deep basement gearing of a 18 speed. A 18 has low end ratios that are similar to typical 10 speed direct drive transmissions which are usually found in front of 2.64 rear ratios. Nice thing with a 18 speed though, there is only 200 RPM spread between gears all the way thru. A 10 direct has 350-400 rpm spread between gears. The 18 provides more functionality by keeping the motor more in the optimal RPM band from the bottom thru the top.

 

I do think Eaton now offers a 13 direct it has a lower first gear to get you rolling

 

It must be a new offering, and in the automated manual transmission (AMT) category. The manual 13 is not offered in a direct drive top gear. I did a quick look at RoadRanger site and did not see one, but you could be right. Please provide a link to a 13 speed direct drive offered by Eaton.

 

I tried to look it up and you may be right I thought you could get in In a new truck but maybe not. I'm looking at ordering a truck with the Dt12 auto shift and it is available in a direct or a single over drive the big advantage to to going with the direct one is it has a 14.96 to 1 first gear ratio where the single over has a 11.10 to 1 first gear. Actually the first gear ratio in the single overdrive is the same ratio as 2nd gear in the direct this low gear will allow you to get moving with a heavy load from a dead stop with 2 64 rears

 

I'll offer my experience. I converted a direct 10 with 2.64 to a 13 when we swapped in the 500 HP Detroit. Overall, our mileage went down with the increase in hp. Startability and driveability went down. In the 10, you could stay in high range in most turns, with the 13 /.264 combination you ended up shifting into low range most of the time.

Overall, not a huge difference, but liked driving the 10 better. If they offer a high torque version of the 10, that would be my choice. The 18, like Cowpie did would be my second choice. The 13 would be the last choice.

 

Do they still make a 9C direct? I know Swift’s Freightliners prior to like 2004 or 2005 ran those with 2.93s, and many dealerships selling their used trucks would do the 13 speed conversion.

 

9 speed convertible is still available. Many TMC trucks were speced with them.