I have an Eaton Fuller RTLO 20918B ..I want to replace the 10-speed one that it has right now ... I would like to know how it would work with an ISX 15 - 450Hp -1650 FT-Lb and Differentials 3.42....22.5 LP tires
So you want to take a 10 speed out and put an 18sp in?? You will have to shorten the driveline, and maybe change the flywheel or clutch depending on the input shaft of the 18sp. But the only thing that will change drive ability wise is you will be able to split gears. Top end speed wont change and it will seem to pull the hills better because of the splits but thats it.