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 Shifting 18 Speed Truck Gearboxes
 JetMech From Australia, joined Mar 2006, 2726 posts, RR: 52Posted Sun Oct 14 2007 03:31:33 UTC (8 years 7 months 3 weeks 13 hours ago) and read 31393 times:

 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
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 Sv2008 From United Kingdom, joined Aug 2006, 622 posts, RR: 0 Reply 1, posted Sun Oct 14 2007 03:49:13 UTC (8 years 7 months 3 weeks 13 hours ago) and read 31387 times:

 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.

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

 JAGflyer From Canada, joined Aug 2004, 3754 posts, RR: 4 Reply 2, posted Sun Oct 14 2007 06:30:58 UTC (8 years 7 months 3 weeks 10 hours ago) and read 31344 times:

 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 From , joined Dec 1969, posts, RR: Reply 3, posted Sun Oct 14 2007 09:36:20 UTC (8 years 7 months 3 weeks 7 hours ago) and read 31281 times:

 Seb146 From United States of America, joined Nov 1999, 14159 posts, RR: 14 Reply 4, posted Sun Oct 14 2007 09:48:29 UTC (8 years 7 months 3 weeks 7 hours ago) and read 31263 times:

 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 From Canada, joined Aug 2004, 3754 posts, RR: 4 Reply 5, posted Sun Oct 14 2007 13:34:28 UTC (8 years 7 months 3 weeks 3 hours ago) and read 31197 times:

 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 From Canada, joined Apr 2006, 487 posts, RR: 35 Reply 6, posted Sun Oct 14 2007 15:30:45 UTC (8 years 7 months 3 weeks 1 hour ago) and read 31169 times:

 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.

 Member since April 2000
 JetMech From Australia, joined Mar 2006, 2726 posts, RR: 52 Reply 7, posted Sun Oct 14 2007 17:23:08 UTC (8 years 7 months 2 weeks 6 days 23 hours ago) and read 31138 times:

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 From United States of America, joined Mar 2004, 3269 posts, RR: 14 Reply 8, posted Sun Oct 14 2007 19:21:00 UTC (8 years 7 months 2 weeks 6 days 21 hours ago) and read 31104 times:

 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 From , joined Dec 1969, posts, RR: Reply 9, posted Mon Oct 15 2007 04:05:03 UTC (8 years 7 months 2 weeks 6 days 13 hours ago) and read 31052 times:

 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.

 JetMech From Australia, joined Mar 2006, 2726 posts, RR: 52 Reply 10, posted Tue Oct 16 2007 05:05:23 UTC (8 years 7 months 2 weeks 5 days 12 hours ago) and read 30935 times:

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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