(9200I) Convert 10 speed to 15 on the hi side?

There is no such creature as a 15 that splits the high side gears. All 15 are deep reduction on the low side. Also the 10 speed ratios are not spaced correctly to be split on the high side they are not even. A 15 speed has a different gear spread from a 10 so if you put a deep box on a 10 it won’t flow the same way through the gears.


The 10 speed case and the 9/13/18 case is made completely different on the back so there isn’t a way to bolt the back box up. You also have to change the gear on the back of top shaft to put a 13/18 box on a 9 speed. Again this gear is different completely from what a 10 speed will use.

 

Rockwell to my knowledge never built a 15 speed. Plus a 15 splits on the bottom, really won't change top end much. Rockwell meritor did have a 13 speed. Think I have only ever seen one.

You really want a eaton fuller 13,or 18 speed.

Now is you trans, overdrive, or direct drive? If its overdrive, a trans swap will not gain you much more than the ability to split upper gears. Less rpm jump. Great for on road. A eaton fuller 15 speed will give you gears splits on the low side. Great for off road. Still not gonna gain alot in top gear. 3.58's and overdrive 10 speed should have you in the high 80mph minimum. If it runs out at 60 mph, it very well could be a direct drive trans. Why idk. Or ecm could be limiting top gear rpm.

Now I'd almost bet the truck with 2.64's has a direct drive. Not ideal for any off road work. But probably fast.

Could be as simple as just put a 10 speed overdrive trans in truck with 3.58s.

I run a 13 speed with 3.58s on LP24.5. Mathematically it should run 100 plus.

 

@wore out dang it. Your post wasn't there when I posted. Guy my slow mind types slow.

 

You’re into a transmission change, but to get where I think you’re wanting to go you have 2 options. 15od or 8od. They both have deep-reduction so you can run high rear end ratios and still lift off heavy without destroying the truck, and their overs. Either one of those transmissions will live forever. They’re natural overs, they don’t have that box of timex parts on the back engaged all the time.

 

The 15 over has a final ratio of .79 while the 8LL and 9LL have .73. I personally love a 15 over. I thought I would hate it as you can’t split the last hole but with 9th being 1:1 with 3.36 rears it was just right on ol 2lane roads the big hole we saved for the super slab. On a big pull I could ease up at the bottom drop to 9th and gas it that was all I needed. It was the most forgiving easy shifting s o b I ever drove. Like the rest of the super truckers I hadda have that big 18 which took a #### and now I have a 13. There ok but sure not my ol 15

 

If the only difference between the trucks, is the rear end ratio, then change that.