why did they use too make 15 speed trannys then stop what were they made for if the use too makethem

Too many "drivers" finding the "hidden" gears and breaking them.


Just a guess,

 

If you truly bought the truck and want to get started AND if you are in Lubbock, get your dot # and some insurance, then grab a belly and get in with the dirt, gravel and asphalt crowd. easy peasy and you will not need an mc # to get started making money.

 

15s were pretty much replaced by the 8LL.

 

Hidden gears??? A driver has to work pretty hard to break a 15 compared to a 13 or 18.

 

In construction type trucks, not many 8lls on the highway.

 

I had a 1998 Century with a 15 speed. I used the deep reduction all the time for reverse, I found the regular reverse too fast when doing tight maneuvers.
They are still available, but only up to 1,650 torque. I've been playing with the numbers thinking of ordering a new truck with it. It would basically have the same gearing as a Detroit DT12 or Volvo iShift but with a slightly lower bottom gear.
As @AModelCat said you can start off in deep reduction and shift up into low range. I use to do exactly as he described. Deep Reduction 1,2,3,4,5; up to neutral, then flip the switch out of deep reduction and carry on into fourth regular.

 

They still make them. Why do people think they stopped? I drove a 2017 T800 that came as a rolling glider with a 15 from the factory. All of the trucks at my old company have 15’s. Deep reduction is great when/if you need it. And in the words of my old boss “Nobody is going to tear up the deep reduction. So when you get a dummy that can’t drive you’re basically rebuilding a 10 speed”

 

I agree. But not many 15s on the hwy anymore either.