jetmech
Topic Author
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Joined: Wed Mar 29, 2006 2:14 am

### Shifting 18 Speed Truck Gearboxes

G'day A,netters,

I was recently watching some videos on U-tube about shifting 18 speed truck gearboxes, as in this video;

I was curious as to how such gearboxes function. Exactly how is the shifting pattern arranged? The driver in the video says he is clutch-less shifting. Exactly how does one successfully pull this off for up-shifting and down-shifting?

http://www.youtube.com/watch?v=sM-kcFxsyCk

This video explains it somewhat, but I'm not exactly clear on the difference between the split function and the high-low range function.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair .

sv2008
Posts: 591
Joined: Tue Aug 29, 2006 11:05 pm

### RE: Shifting 18 Speed Truck Gearboxes

 Quoting JetMech (Thread starter): This video explains it somewhat, but I'm not exactly clear on the difference between the split function and the high-low range function.

I think there is just another gear between the gearbox and final drive - so it doesn't change the gear ratios at all, but effectivly makes them all lower by altering the final drive ratio (lowering it for low range).

So an '18 speed' gearbox would only have 9 gears really, plus the hi/low drive gear (which cars don't have), plus the final drive. 18 gears would be far too heavy.

Not sure about split function.

[Edited 2007-10-14 03:52:20]

JAGflyer
Posts: 3486
Joined: Tue Aug 10, 2004 5:31 am

### RE: Shifting 18 Speed Truck Gearboxes

If I understand correctly there is a pattern with 8 places to shift. To get into the higher gears you flip the switch on the side of the shifter and move it into the corresponding position. The layout for a 16 spd is something like this:

9 10 11 12
R 1 3 5 7
| | | | |
R 2 4 6 8
13 14 15 16

To access (9-16) you flip the switch on the side of the shifter and then push it into the correct position. Each position is used for 2 gears depending on what position the switch is in.

This pic maybe can help illustrate what I mean

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checkraiser
Posts: 814
Joined: Mon Mar 14, 2005 1:35 am

### RE: Shifting 18 Speed Truck Gearboxes

An 18 speed is really just a glorified nine speed. Once you understand how a 9 speed works it's easier to understand the principle behind the 18 speed.

Here's the pattern for a nine speed:

Low range:

R 1 3

L 2 4

High range:

R 5 7

X 6 8

(yes, there are two reverse ratios. The X isn't a gear you use (you can, but its ratio doesn't "jive"))

If you look at the pic posted by JagFlyer of a 10 speed (by far the most common trans in North America) you'll see a switch for high and low range. You start in low range and run the pattern, when you're in the highest gear in low range (4th on a 9, 5th on a 10) you pull the switch up to high range. The switch is air powered; you pull it up before your next shift and when you move the lever through neutral you'll hear a chink and high range is engaged. Once in high range you repeat the same pattern (in the 10 speed 1st gear is now sixth, in the nine speed 1st gear is now 5th.)

These transmissions are basically just five speeds with an air actuated reducer which doubles the amount of ratios available.

Now, an 18 speed (and to some extent, its close cousin, the 13 spd.) allows you to "split" each gear. On these transmissions there is another switch on the shift lever operated by your left thumb. There is 1L and 1H, 2L,2H, etc... These "split" gears are like a half step between a full gear change. When you use the splitter you do NOT use the clutch (doing so will not accomplish the shift, just a lot of grinding.)

Because engines are becoming more and more powerful, especially on the low end, the practicality of an 18 speed just isn't there any more. Even the more useful 13 speed is a dying breed. Ususally only owner operators spec an 18, and it's really more of a "coolness" thing than a matter of practicality. BTW, in a 13 speed you only split the high range gears.

To address the clutch issue one must understand that truck transmissions are non-synchronized **. You cannot simply push the clutch down, move the lever in one motion (like in your car) and happily go on your way. Engine speed must match the gear you are shifting in to otherwise it won't engage, it'll just grind. It's not something you can learn from a book - it just takes practice.

To match your engine speed to the road speed of the desired gear you either have to double clutch or not use it at all. Not using the clutch is a practice called "floating" and I'd guess that about 75% of drivers "float" the gears; I'm one of them.

This page has all of the data you could ever want to know about the Roadranger 18:

http://www.roadranger.com/Roadranger...sions/low-inertiasuper18/index.htm

**I understand that many, maybe even most, of European tractors have synchronized transmissions. They were a miserably failed experiment on this side of the planet.
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seb146
Posts: 15559
Joined: Wed Dec 01, 1999 7:19 am

### RE: Shifting 18 Speed Truck Gearboxes

About using the clutch: They taught me to double clutch at truck driving school. When I got a real job, they said it was not necessary, so I quit using the clutch. I got one of those infernal paddle shifters and HAD to use the clutch sometimes. I hated that transmission! But, not using the clutch was easy. The diesel engines are geared so differently, it is easier to not use the clutch.
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JAGflyer
Posts: 3486
Joined: Tue Aug 10, 2004 5:31 am

### RE: Shifting 18 Speed Truck Gearboxes

You would need to use the clutch when starting from a stop, going from forward gears to reverse and vice versa, correct?
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AC777LR
Posts: 825
Joined: Sat Apr 29, 2006 10:07 am

### RE: Shifting 18 Speed Truck Gearboxes

 Quoting JAGflyer (Reply 5):You would need to use the clutch when starting from a stop, going from forward gears to reverse and vice versa, correct?

You are right, I only use the clutch for Starting and stopping. The Eaton Fuller transmissions have what is called a Clutch Break that stops the gears from moving when the truck is at a stop. Never press the clutch all the way to the floor when you are moving the truck.
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jetmech
Topic Author
Posts: 2323
Joined: Wed Mar 29, 2006 2:14 am

### RE: Shifting 18 Speed Truck Gearboxes

Thanks so much for the input everyone!

 Quoting JAGflyer (Reply 2):This pic maybe can help illustrate what I mean

Is there any sort of inter-lock that prevents you from accidentally shifting between Hi and Lo range when you are in a given gear? It looks as if it would be possible to shift up or down 5 gears in one go if you were not careful.

 Quoting Checkraiser (Reply 3):These "split" gears are like a half step between a full gear change.

How are gears split? I can picture Hi and Lo range as an additional two speed gearbox mounted after the output shaft of the main gearbox, but exactly what is the mechanism that splits an individual gear?

 Quoting Checkraiser (Reply 3):To address the clutch issue one must understand that truck transmissions are non-synchronized **.

With truck gearboxes, are you sliding the entire gear in and out of mesh, or just a dog clutch?

 Quoting Checkraiser (Reply 3):either have to double clutch or not use it at all

Do you need to double clutch up-shifts and down shifts? I double clutch downshifts on my car, but the gearbox would definitely have a synchronisation mechanism.

If I understand the information in the link you so kindly provided, if I was shifting from 4 Hi to 5 Lo, I would need to move the split from Hi to Lo in addition to the range shift whilst simultaneously moving the stick! How do you possibly manage to smoothly pull of the three operations at the same time? Again, is there any mechanism to prevent you accidentally range shifting in a particular gear, or is it up to the driver alone to keep track of the gear they are in? It looks like you could shift eight gears in one go if you were not careful. Very interesting link BTW   .

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair .

Go3Team
Posts: 3156
Joined: Sun Mar 14, 2004 1:19 am

### RE: Shifting 18 Speed Truck Gearboxes

 Quoting JetMech (Reply 7):Again, is there any mechanism to prevent you accidentally range shifting in a particular gear

No.

 Quoting JetMech (Reply 7):or is it up to the driver alone to keep track of the gear they are in?

Yes.

 Quoting JetMech (Reply 7):How do you possibly manage to smoothly pull of the three operations at the same time?

It does not need to be one fluid motion. Flip the range switch, then split the gear when moving the gear shift. Its all pretty easy.

 Quoting JetMech (Reply 7): It looks like you could shift eight gears in one go if you were not careful.

You can only shift into a gear as long as the RPMs are matched. No match, no gear.

 Quoting JetMech (Reply 7):Do you need to double clutch up-shifts and down shifts?

For those that use the clutch, yes.

 Quoting JetMech (Reply 7):I double clutch downshifts on my car

Not necessary.

 Quoting JAGflyer (Reply 5):You would need to use the clutch when starting from a stop, going from forward gears to reverse and vice versa, correct?

Yes.

 Quoting AC777LR (Reply 6):The Eaton Fuller transmissions have what is called a Clutch Break that stops the gears from moving when the truck is at a stop.

Not just Eaton Fullers.

 Quoting JetMech (Reply 7):but exactly what is the mechanism that splits an individual gear?

I don't know much about the mechanics involved, after all, I'm just a steering wheel holder. I imagine it's similar to the range selector.
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checkraiser
Posts: 814
Joined: Mon Mar 14, 2005 1:35 am

### RE: Shifting 18 Speed Truck Gearboxes

 Quoting JetMech (Reply 7):Is there any sort of inter-lock that prevents you from accidentally shifting between Hi and Lo range when you are in a given gear? It looks as if it would be possible to shift up or down 5 gears in one go if you were not careful.

There's no interlock per se, but it is impossible to blow thru five gears in one go for two reasons. First of all, and this is something a lot of people don't realize, as that moving the range selector while you're in gear does nothing. You'll hear a little hiss of air but the range doesn't change until the shift lever passes through neutral. Secondly, for argument's sake, if something malfunctioned and it did try to change ranges at an inappropriate speed the gears would never mesh. The trans. would likely have some sort of catastrophic failure at that point.

 Quoting JetMech (Reply 7):How are gears split? I can picture Hi and Lo range as an additional two speed gearbox mounted after the output shaft of the main gearbox, but exactly what is the mechanism that splits an individual gear?

Your vision of Hi/lo range is right on the money. That's exactly how it works. I'm not a mechanic and really couldn't explain the inner workings of the splitter, but if I had to guess it's probably similar to the range gearbox, but likely "before" it and without such a drastic ratio change.

 Quoting JetMech (Reply 7):With truck gearboxes, are you sliding the entire gear in and out of mesh, or just a dog clutch?

Beats me. On that page I linked there is a video and in the first few minutes of it they show a disassembled trans and how some of the parts move. Maybe that would answer your question?

 Quoting JetMech (Reply 7):Do you need to double clutch up-shifts and down shifts?

Yes, no shift can be accomplished without matching your RPMs to road speed.

 Quoting JetMech (Reply 7):If I understand the information in the link you so kindly provided, if I was shifting from 4 Hi to 5 Lo, I would need to move the split from Hi to Lo in addition to the range shift whilst simultaneously moving the stick! How do you possibly manage to smoothly pull of the three operations at the same time?

I didn't elaborate on splitting. To split from L to H you move the splitter switch forward and simply release the throttle. The engine will drop about 200 RPM and H is engaged. Get back on the throttle and go. To split down you move the switch back, release the throttle, it will sort of "freewheel", once you realize it's disengaged throttle up about 200 RPM above where you were before and you'll feel L engage. If you're doing a gear change with a split it just kind of goes together as long as you match your RPMs right. Say you're shifting 6H to 7L, you'll move the splitter switch back, move the lever into neutral, allow about a 200 RPM drop and move the lever into 7.

The shift you described is the most difficult to accomplish and would be performed like this: On this shift you'll take the truck up more revs than normal, say about to 1800 RPM. You would move the range selector to high range, then move the gear lever into N. While in N you'll let the engine drop 400 RPM then move the lever to 5. You'll be in 5H, then you'll immedialtely split down to 5L.

Again, I'm no fan of 18 speeds because in the vast majority of applications they're overkill. There would rarely be a reason to split any gears in lo range. Lo range is geared so low that going wide open in top gear in lo range will only net you about 15-20 MPH. The only way I can see splitting gears in lo range would be to get a fully loaded road train moving on an incline. The 13 speed was a much more common trans here because the real need to split gears only comes in the top two or three holes.

Both of these transmissions are quickly falling by the wayside, as I said before, today's engines don't require them unless you are operating in some extreme application. Inexperienced drivers will tear them up and they have a shorter warranty. The Roadranger 10 speed (found in about 80% of US trucks) has a 5 year/750k mile warranty. The 13/18 speed only carries a 350k warranty. Out of 40 tractors I have one 6 speed, one 9 speed, one 13 speed (with a for sale sign on it), four 10 speed automatics and the rest are manual 10 speeds. That's how prevelant that trans is in the industry.
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jetmech
Topic Author
Posts: 2323
Joined: Wed Mar 29, 2006 2:14 am

### RE: Shifting 18 Speed Truck Gearboxes

 Quoting Checkraiser (Reply 9):

Thanks again Checkraiser   .

 Quoting Checkraiser (Reply 9): Your vision of Hi/lo range is right on the money. That's exactly how it works. I'm not a mechanic and really couldn't explain the inner workings of the splitter, but if I had to guess it's probably similar to the range gearbox, but likely "before" it and without such a drastic ratio change.

Yep. I checked the Eaton service manual (from the link you provided) for the 18 speed transmission and that's pretty much how it is. Basically, there is the forward gearbox section with 5 distinct forward ratios plus reverse. The output of the forward gearbox goes into the aft gearbox section. The aft gearbox section has two sets of closely spaced ratios for splitting, followed by one set of gears for Hi / Lo range. Lo range goes through the gear-set, whilst Hi range is direct drive. This gives 20 forward ratios, but only 18 are available as there is no range shift for the lowest forward ratio.

What I found most interesting was that Eaton were able to arrange the gear ratios of all three gearbox sections to not only get 18 distinct ratios, but to also get the spread of the ratios how they wanted (more ratios down low and less up top). My pushbike for instance has 21 speeds, but about 40% of them are almost duplicates.

 Quoting Checkraiser (Reply 9): Beats me. On that page I linked there is a video and in the first few minutes of it they show a disassembled trans and how some of the parts move. Maybe that would answer your question?

Eaton use dog clutches to engage gears, which is the same as car gearboxes. All the gears in the gearbox are constantly in mesh (except reverse) and it is the sliding dog clutches that lock the gears onto the shafts.

 Quoting Checkraiser (Reply 9): Again, I'm no fan of 18 speeds because in the vast majority of applications they're overkill.

Fair enough, but it would sure be interesting having a go at driving a truck with such a box! Anyway I thank you for all you fascinating input. I have Googled the subject many times but never found the link you provided.

Regards, JetMech

[Edited 2007-10-16 05:07:09]
JetMech split the back of his pants. He can feel the wind in his hair .

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