18 speed mack

The Mack 18 in high split is the exact same gear ratios as the Mack 9. The only difference between the Mack 13 and Mack 18 is the pin in the shift knob that locks out the high split in the low range for the 13.

As long as you aren't lugging, it won't hurt anything by not splitting the gears.

 

The gear ratios are different. The EF has more differences between the transmissions, too.

Still won't damage it by not splitting every shift, though.

 

She have mack rears too? My dads looking at a 1999 set toward axle ch with mack 18 and mack rears.

 

You'll feel when you need to split the gears.

My advice is to use the low low reverse when you're loaded and Low low gears when you are off the road and use a nice low gear to pull out to be easy on the clutch.

I love those kinds of Transmissions. You always have a gear for every road speed.