Ihc 9400 1995 cummins n14

Good, too many times I hear people getting a truck and then find out no one can use it because of the reliability issue.

 

9 spd with 3.73 on 22.5 tall rubber was a common regional fleet spec up here for 350-400 hp Cummins engines bitd. 355 were more common on long haul CAT powered highway trucks.

 

Alright, I'm late to this party but we had a truck with 4.56 rears and a double overdrive 18 speed. Top gear was .73. At 75 mph it was running 2100 rpm. At 70 mph it was running 1800 rpm. You would be better to change the rear end gears. Unless the trans you have now is a direct drive and the trans you want is something lower than a .73 then you won't have changed much. You can get the model number off of your transmission and look it up online here
Ratio
Compare it to the model that you want and see if the final drive ratio is any different. If it is not then change the rears. Chances are it isn't different.

The size of the tires on the back play into this. The taller the rubber the less aggressive on the down speeding that you need to be with the gear ratio. An example is that you wouldn't want to go to a 3.23 gear ratio in the rear end if you have the tall 24.5 tires. If you had the 22.5 lo pros then a 3.23 wouldn't be out of the question.

 

I would say that's the safe bet. If the 355's are half the price than you could go that route wuth lo pro 22.5s. But then you would probably be putting the 13 in it sooner rather than later. Good luck on it.

 

So youre saying if I put 24.5 talls on my truck to get a little better gear ratio and run 70 in direct and not overdrive I might get a little better fuel mileage?

 

i won't get into the tire thing but direct drive always returned better mileage for me in my fleet.