Converted 9 sp to 13 sp into an 18sp?

The low side of the splitter is under driveing the main gear that the tranns is in. The high side of the splitter is direct drive. The only thing that is "over drive" is the main trans gear in the high gear possision. In 8th gear high split (13th) the splitter is in direct and the trans has an over drive of .73. In 8th low split (12th) the main gear is sitll .73 over but the splitter is in under drive giving only a .86 over drive. Hope this helps ya.

 

Yes they did this when they went to the "new style" 13-Speed. They essentially combined the RTX Version (Standard H-Pattern) 9-OD with the 13 Direct Splitter. This allowed them to only drive one overdrive set (Main Box) when in High reducing friction and increasing fuel mileage while getting a taller overdrive and wider range.

The new RTLO is sometimes called a Double Overdrive but they are not really like the old RTOO that had a 0.73 OD in the box and a 0.85 in the splitter . I used to have a 444 Cummins with one of the old RTOO with 4.33 and it still only turned 1350 rpm at 65 rpm.

RTLO 13-Speed Gear Ratios
7-Hi (11th) - 1.000 (Direct in Both)
8-Lo (12th) - 0.855 (Overdrive Main / Underdrive Splitter)
8-Lo (13th) - 0.731 (Overdrive Main / Direct Splitter.

The RTLOC T2 (9-Speed Convertible) used by Werner actually used the Splitter controlled by the PCM when in the Top Hole. I have a buddy who bought one of their trucks and drove it for a while before converting it.

 

Sorry I a noob and trying to get my post count to 2 so I can reply with pics. Here's #1.

 

Sorry I a noob and trying to get my post count to 2 so I can reply with pics. Here's #2.

 

Very, very interesting Hammer. Thanks, you've gotten me in sponge mode.

I think I'm following. If I understand correctly, this is the gearset you're talking about:



I copied the image from the 18 speed power-flow diagram for stick 1, low range, high split. This is where the center gear is driving the outer gears, which in turn drive the range gears on the right, which in this case are in LOW (small outer gears turning larger inner gear). This is the flow that you can't get with a 13 speed with stock knob.

Then when you're in high range, low split, you have this:



Like you said, the power is flowing through that gear set in the opposite direction from before, with outer gears driving the inner gear, and then on to the range gears via the center "clutch", in HIGH mode (I think they forgot the flow line through the range section -- I've added it in green).

So, our gear set in question is the direct, or high, side of the split, right? I see the other splitter gear set to the left to be the underdrive, which I would expect to have a slightly smaller center gear and slightly larger outer gears.

The question is, can we make our 13s into 18s by simply changing those three gears to the stronger ones, and changing the shift knob? Those outer shafts would already have to be equivalent since they're handling the low-split/low-range, right?

Edit: I re-read your post and saw you said the 18's aux section housing was different. So it's a no-go unless you change more stuff?

Cheers,
-GL

 

You've got the right gearset GL. Back up there ^^^ Rockhauler said they put a 18918 aux shaft in his 18913, so you might be able to just change the guts. That shaft has a different part number but identical dimensions, so there is most likely some alloy/treatment/finish variation. So high torque in high-split/low-range (think about the flow, that gearset carries no load in high/high,) could be an issue if you didn't change both the shafts and gears. More than likely a durability issue came up in testing, and would likely be a minimal issue for OTR use, as it's unlikely the tranny would spend much time there.

Without having both cases to look at, hard to tell why they're different. If I remember correctly, they show different bearings, so I'd guess the outer race might be different, or it could just be a stronger case with identical dimensions. Also, the center gear in that set rides on a bearing in the 18 vs. on the shaft in the 13.

 

hi i have a question i see plenty of trucks with 9 speed ,what is better for o good mpg 9 speed or 10 speed

 

Man, maybe my head is on backwards but since the range is AFTER the splitter, wouldn't the aux shafts and splitter HIGH gears be loaded more in HIGH range LOW split than LOW range HIGH split?

Here are the pics again.
High range low split. I see this as the heavier load on the aux shafts and high-split gears since they drive the output shaft directly. The range section being like the rear gears on a bicycle in high gear, and the splitter being like the pedals -- hard to pedal:



Low range high split. I see this as the lighter load on the high-split gears and aux shafts. They're driving the low (easier) side of the range gears. The range section here being like the rear gears on a bicycle in low gear, so the splitter is much easier to "pedal":

Gerardo, I'm sure someone else can answer better, but I think it would depend on the entire truck setup, engine/tranny/rears, and also the driver of course. All other things equal, I personally like more gears so I can keep the rpms optimal more of the time.

Cheers,
-Glenn

 

I guess I made the mistake of reverse engineering. My thinking was that gear must be more heavily loaded and that's why there is a bearing there on the 18's. Never stopped to look at the actual loading, but you're right, I think. The multiplication of the underdrive low split and the higher resistance of the direct high range would indeed increase the load that gearset carries. So why the bearing? Drive/driven shouldn't really matter that I can see. Yet that is the structural difference between the two.

Time for more pondering...

 

Yes, looking at it from a loading perspective, the 13 speed's aux shafts and high split gears already DO handle the heavier loading (high range low split) with stock knob. It looks like changing the knob would simply also let you use them in the configuration where they're under less stress (low range high split). I can't see anything wrong with it at this point. But yes, more pondering...