Pros/Cons of Converting 9-speed to 13-speed?

I have a 2014 Freightliner Cascadia with a DD15. I’ve heard people say that a 13-speed will be more fuel efficient. I suppose this could be true as higher gears consume less fuel (but have less power). In a 9-speed, the highest gear is 11.1%, while on a 13-speed, the highest gear is at 7.7%. Assuming this were to be true, it could give my MPGs a good boost.

My trainer had a 13-speed, and I remember him driving it like a 9-speed. Was he driving it wrong? One would think you would have to hit all 13 gears. By the way, when I say 9-speed, I am referring to the 8-speed most truckers appear to call based on the numbers on the gear stick.

 

13s would be a bit better for climbing faster, and finding the most efficient RPM for a given speed, but not much more. If your transmission already keeps you at good RPMs and you're fine with it's climbing speed, then it shouldn't be a big issue.

 

Converting a 9 to a 13 is not going to change your final ratio.

 

One way to help decide is to first know max torque range of engine. Probably 1100-1500 rpm or so. Goal is to stay in range.I don’t like to Lug too much on a hill. Despite Detroit’s claims of better mpg. Too hard on Trans. Depending on your Operations Weight, Hills etc. determine if dropping only half as many RPMs (1750 vs 3500 roughly) will help You top most Hills or not. In other words if you can just split it down once. Otherwise if still needing to drop whole gear mpgs may not improve. Overall drivability is enough reason to Me for the upgrade. Back When I ran all flatlands 9 spd was just fine. Long legged 8 th gear was a fun drive with 390s and bullet proof. There’s a reason most New Truck warranties for 13 spd are less than 9 and 10 spds 350 k vs 500 k .

 

If your truck has one of the 9 speeds that just has the 13 blocked out, conversion is cheap and easy to do. No reason not to and it will help on hills.

If you have a 9 speed that can’t be converted, that will either require a complete transmission swap, or at least swap out the back of the transmission. Lot more involved in this. If this is the case, and the truck does fine as it is, you may want to leave it alone.

Yes, you can shift a 13 just like a 9, and most do when the gear split isn’t needed. There is no con in swapping a 9 for a 13, other than cost (depending on what 9 speed you currently have).

 

With a 9 speed convertible, is 9th gear going to run in the same rpms at the same speed as 13th would with the conversion done? Looking to do this also, but would like to see a gain in fuel economy for it. Running from Michigan to Alabama, Texas, Missouri and back mostly

 

7% would be a 13 double overdrive, no?

 

I have never heard of a nine spd with the 13 spd blocked out. At the very least you have to add the back box to convert one, which the 9 does not have. All 9 spd's are not created equal either, and you can not convert all of them at all.

 

The three Eaton convertibles are RTOC-16909A, RTOCM-16909A and RTOC-18909A. Top hole In the converted 13 is .73 same as the 9 speed.

 

My 9 speed has the C in the serial for conversion. The box is already there, just needs the shifter head changed and air lines ran. It’s actually very common with the trainer schools. Easy to learn, and once they sell the trucks, it’s a $500 conversion to a 13

So basically short of changing to a big 13 or swapping rear end, I won’t get any less rpms at 65 on the 13 vs 9?