This will go down on my permanent record...

Well, think of it like this.......you've got a heavy load and you're coming out of a truckstop........engine is winding out but not enough to shift. You hit that button and all the sudden, you have a half gear and you can roll on. A 13 speed is just a 10 speed with a half of a gear. By the way, you don't have to use it all the time. But it does come in handy as hell from time to time.

 

A 13 is actually a 9 that you can split the high range gears.

 

What do you have for rear end gears? Make sure to match your transmission ratios to the rears.


13 is not that hard to learn.

Botton side, regular gears.
Top side you can split. Think of it as a half a gear taller. In 7th, the splitter down, 7th gear direct, flip the splitter up, 7th overdrive.

 

Should be on the metal tag on the differential, or on the data plate in the door.

It’s really a good idea to match transmission and rear gears.

Eaton-Roadranger used to have a calculator tool you could use to estimate road speeds at RPM.

 

Here is a few of them .

Calculators | Spicer Parts

 

I had 3.25 and 13 speed in my blue pete. Perfect specs for a highway rig. If u still do lots of westcoast running you will enjoy being able to split the top side when pulling a mountain. Instead of 500 rpm difference between gear the split will be around 250 . Makes it easier to keep the engine in the horsepower band in high rpms rather than having to lug it down to 12-1300 to be able to downshift