Is it bad to skip gears while loaded (13 speed)

Sorry, had a blown bag when i came out this morning, busy day. Will try to make some time if i get to my drop tonight.

 

Alright lets start with the mainbox



The clutch end is bottom of picture. So the power comes through the clutch and input shaft, into that center gear shown at very bottom. This is floating in constant mesh with the two countershafts on each side of it.

The gears on the countershafts are all splined to the countershafts and in constant mesh with their mate gears on the middle shaft, which id call the intermediate shaft. Each gear on the intermediate shaft can be freewheeled or locked to the shaft via a sliding clutch that dogs into the freewheeling gear's inner diameter, which is splined also. the sliding clutches are the small ones with a groove in the center for the shift fork. They release one gear, go to neutral meaning disengaged on both ends then slide across to engage the other gear. This is what you feel grinding in the shaft handle. only one at a time may engage. If two gears engage simultaneously it will lock the trans and stall engine or explode teeth, and yes it can happen with worn shift forks and shifter bushings.



Where all 3 gears across are the same tooth count is your direct because there is a 1:1 ratio between countershaft and intermediate. 3/7 is that hole on an RTOO9513. 7th is technically it's overall 1:1 "direct" ratio (meaning trans output speed matches engine output speed in this case.. The word 'direct' is overused in these things.) 3 and 7 are the same gears in the front box. Only your selection in the rear box decides if youre in "3" or "7" since range and split is in the aux section and are both air servo forks. The "front" or "main" box is a stick shift only affair. Air does nothing in your main. Similarly, "low" and "cheater gear" are the same in the front box.



Anyway at the top of pic in the center shaft is where that steel web is, your main box outputs power into the center of you auxilliary rear box's input side. A 13speed is really a 5x3 made into a single unit but we only count the primary 9 forwards plus 4 splits on the top side.


So 5 forward ratios and 1 reverse in the front. Multiplied through one of 3 gears in the aux.. Low. Direct or OD. However you can only choose one at a time, hence no "splitting" of the low side. When you choose to "split" you are choosing a slightly faster final multiplier gear than the "direct" ratio. But either low or direct or OD. Low and OD are very far apart in ratio, so you cant jump between them like you can with direct and OD. Jumping from direct to od and back to direct is "splitting" because theyre a half step apart. 17% spreads instead of 34% like a 9 speed. 250 rpm steps instead of 500 rpm.

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I had a chain drive wallet once... For about 2 days. Then the chain got caught on the seat frame as I was jumping out of the truck and I did a face plant into the gravel lot of the stock yard. The last time I saw that wallet it was on a 1 way flight to the manure pile.

 

Every truck driving school should have a transmission opened up like that for students to see and play with. The first time I saw one opened up my brain when AH HA!! I was already proficient at shiftimg and had been driving for many years. But it just made so much more sense as to how it all worked once I could see and play with it. I gave myself blisters spinning the input shaft so I could "shift it" with a couple of hand held forks.

 

This is the aux box, back box, auxilliary, whatever. it is your 3 speed multiplier. Think of a 5speed car tranny with a 3 speed Tcase behind it. The tcase normally stays in "drive" but it also says "low" and "fast" on the shifter. Now put that together in one unitized module and you have a roadranger.





So how it works is this. The main or front countershafts are independant of the aux or rear countershafts, though inline physically. The aux countershafts are fed power by a gear in the center of them that is not pictured here, (it is in pic 5) which is splined to the output side of the front box's intermediate shaft.

This gives eaton the choice to overdrive or underdrive or 1:1 drive the countershafts in either front or aux box. RTOOs are noisy and inefficient due to overdrive ratio in the countershafts themselves, not just the gear sets. There are 3 ratios above 1:1 so its truly a triple OD.



Now, on the left or passenger side that air line into the servo moves the range fork. In that fork is the low range syncronizer assembly which helps decelerate the low range bull gear and mesh it rapidly. The friction surface inside the aux bull gear's ID wears out and then the teeth grind which is shown here. Its a pricey gear.






If you flip from low to "high" you are using the direct gear by uncoupling the bull gear and letting it freewheel, then sliding over to lock the aux mainshaft (which is what the driveshaft yoke is splined to) directly to the front box's output shaft, what i call the intermediate. At this time the splitter gear and bull gear are both floating and the aux direct gear is locked in.

 

On the right or drivers side is the piloted air servo that actuates the splitter fork. Its been about 6 years since i took these so im foggy on some parts, which moves forward or back to do what, but this is a bottom view looking at the splitter fork


I remember that little spline section can be locked to the aux output or freewheeled and you can see the bearing in the above pic. I cant remember what the bull gear engages to but i know these parts are why you cant split low.



This is whats behind the bull gear and im just about certain these three gears, well two countershafts and one gear, at the very back of the case make your OD ratio.. Your "split up" gear. Could be wrong but i think thats it.


Today I glanced at an 18speed aux we have wrapped up and its obviously very different, somehow

enabling a split of both high and low range.




Anyways, this is whats in em and if you can tell me how cheater gear is weak i am all ears. I myself cannot find it but i have certainly been wrong before!

 

You've done a very good job of explaining how a non-synchro, constant mesh transmission works, except according to what I have seen from Eaton videos explaining it, that doesn't sound like how direct works. The Eaton video says there is a collar that locks the input shaft to the output shaft. The torque map then is just straight down the shaft, and not through the counter shafts.

 

well i did point that out though not terribly clear. My thoughts arent clear either, theyre clouded with excess detail. I explain that 7th is the overall direct gear in an RTOO in my first post, that its a 1:1 ratio of driveshaft to crankshaft. Its not one collar tho, its two. You have to engage the intermediate shaft to the input, 3rd hole in the front box, and lock the aux output the the intermediate shaft which is middle speed in the aux. Meaning high side, splitter back. Power will flow straight through at 1:1 ratio rather than over or underdriven via countershaft multiplier.

 

Again "direct" is an overused term that can mean a few things with trannies so it can create cloudy verbage.