15 speed explanation

Its essentially just a 10 speed with 5 "deep reduction" gears.
Most cases you'd just run it like a 10 speed.

The deep reduction gear ratios overlap low range so if shifting from lowest gear to highest, you'd only use 12 of the 15 gears.


These would be the gear positions you'd hit with the gear shift if going lowest gear to highest gear:

DR: 1-5
LR: 4-5
HR: 1-5

 

Easiest way to shift 15

 

My truck has an RTO-15615 15 speed in it. If you look at the rebuild manual it actually applies to the 10 and 15 speed transmission of that design level. Main box is the same, only difference being 2 speed aux in the 10 speed vs 3 speed aux in the 15 speed.

 

Yep you basically just drop one gear back in the main box when upshifting out of deep reduction to low range.

 

The bag of #### 15 speed is similar to an 8LL just based on a ten speed, it has a tall low low and a short OD and a bunch of dog #### ratios in the middle, which is why they were canned for the 18. Your best bet is to start in deep reduction then shift to the regular low side in neutral as you go back a gear, i usually go 1-2-3 then back to 2, if it’s flat I go to neutral and go back to the same gear.

don’t forget where the gears are if your driving different transmissions....
that video is of a direct or has a new cover on it, the over drives shifted high gear
Against the dash and 1:1 against the passenger seat

 

I drove them in the oil field. Only in snow or rain I would use the DR. The clay would stick to everything and it wouldn't turn unless you turn using the Dr. Plus the spacing between all the gears is more even. In a 10 8,9,10 have a lot seperation between them , which I don't like.