Transmissions

I am going take a wild stab here and say no. In a way, you may be able to go from a 13/18 down to an 8. I’m guessing disconnect the splitter, and you are basically there.

 

There were a bunch of convertible 9 speeds put in fleet trucks. They were a 13 speed without the the splitter knob and lines. back then it ran under $100 in parts, usually a shop would do the upgrade for under $200 out the door. Fleets did it is a way to increase resale value that would keep the trainees from messing up the trans.

Beyond that "upgradeable" trans I think you are looking at a swap.

 

You can't claim to be a dirty old trucker until you've blown a tranny or two... or so I've heard.

 

Its sat night, I'm grilling and mowing. Yes they had the 9 convertibles. But most all standard rt,rto 9 speeds can be made into a 13, 18 for more money. You change the rear box. Which then you must shorten the driveshaft. FRO is not convertible that I know of. Or I never had a reason to check if it was. Still have to verify ratios and torque rating.

 

Go to Eaton's website, and you can find the repair manuals w/ part# breakdowns. IIRC, the only structural change from an 13 to 18 is there's a bushing in a 13 that's a bearing in an 18, between the splitter and range sections. It's there for the unique power path of low range/ high split which introduces higher speed differentials than within the 13. The gearsets are different, of course, and there's the splitter interlock in the air system of a 13.

I don't know much about the 8LL other than the splitter is where the deep underdrive comes from.

And don't forget that the Super 10 is of that same family. It only has a 3 speed main with a wide ratio splitter. The range shift is controlled by the shifter when it's moved between the 2nd & 3rd gates, and those two gates used the same 2 gears in the main. That feature was why it got stuck with a bad rep. Guys coming down ramps would kick the stick to neutral at too high of speed and the synchronizer would come apart, leaving you stuck in high range.

 

Awesome, i qualify...

Not my fault, warned the owner it was on its way out for 6 months...