I thought you were big and ugly enough to let it through. 
For today, but best we donāt mention the subject again. 
We wonāt mention it but itāll come up anyway. Iāve been on this āhell is other peopleā forum for over twelve years and CF was already a fixture when I arrived. A forum without a nemesis is like a gin without angastura bitters 
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I wish Iād found this video earlier.
He confuses himself a bit and called the deep reduction switch a splitter,but immediately corrected himself. He does know what he is on about.
A chart comes up, but no video.
Try this, it was embedded in the link, but I went direct to YouTube.
Jesus! A nightmare communicator - all over the place, but yes, he does just about cover it; and he certainly supports everything you and I have been saying about the various Fuller options.
One odd thing he does is to try and explain the reversed top two gears in the 9-sp RTO (overdrive) box. He seems to think it gives better performance (in cement trucks!). No. The top two gears were reversed, giving a U-shaped instead of H-shaped shift to ensure that you got a direct top gear to reduce wear on motorway work. This was cured 45 years ago with the ingenious RTX box which automatically crossed the linkage over to create an H-pattern with a direct top gear. The RTX coincided with multi-mesh which made the RTX 11609 / 14609, RTX 116013 etc a brilliant 'box to use. Loved it.
He also talks about what CF was referring to: the cross-over ratios in the 15-sp 'box. This also occurred in some installations of the 13-sp 'boxes, which were described as āunderdriveā as opposed to overdrive. So youād get some split-shifts that were equivalent to the gear youāve just changed out of. A bit like what the man in the video meant when he said you could change into crawler in a 9-sp 'box in high range to save having to do a range-change down to top gear in low range on a hill. The ratio was the same but you could save time and revs by cheating. It worked.
Also, interesting that he described the 18-sp Fuller as an unblocked 13-sp box. That makes sense as the low range is split as well as the high range.
All good stuff. Fuller Roadrangers for ever!
That applied to all, 9, 10, 13 and 15. RT was direct top, RTO was overdrive. Each could be converted to the othe by swapping the top two gears, internally. We called the overdrive a āround the cornerā box.
Was that the chrome knob with a three position switch for Low, intermediate or direct? I had one in the first semi I drove, but canāt remember the shift pattern.
It could be done in a 13 as well, but I only did so when unloaded, as itās not as strong as the correct way. We called it the āsecret gearā.
How to decipher RoadRanger models. I never knew what the number between the torque and ratios was.
Thatās how it comes out when you havenāt done a lesson plan. As you would know, the plan takes longer than the lesson.
To be fair I didnāt anywhere state having any personal experience of the Fuller 15 speed.
Unlike 9 and 13.
Anything related to the 15 speed would have to be from second and third hand information.
It was just unfortunate coincidence that there is as much, incorrect, information, by those who have the experience even with video evidence, but who themselves donāt quite get what they are driving or describing.
Combined with the idea of a 15 speed range change of any type being unfathomable for a European with familiarity with Spicer, Fuller, ZF 12 speed, Scania 10 speed and assorted 16 speed, splitter and range change/splitter types.
So I understandably put 2 and 2 together and got 5.
Also itās difficult to get into perspective closer to 100t gross weights sometimes also combined with loose soft ground.
Iām happy to admit that I got this totally wrong but equally my very real truck manufacturing sector experience, finally helped me to understand it and look further into those misguided observations by others.
Contrary to my initial, incorrect, ideas itās actually the most logical transmission design to get a big weight moving from a standstill and without losing important momentum between shifts even on tarmac given the choice between the 9 speed, 13 speed v 15 speed.
Meanwhile the original post mobility scooter and drawbar trailer was the perfect example proving the advantage of train weight
As for the Detroit two stroke picture the mad keen 16 year old wannabee driver CF hearing a 16v71 fire up for the first time.Magic is the only word to describe that motor and what makes it work and finding out all about it was my first mission during my own time off.
Magic is not the reason any engine works.
With a wee bit more time-off. you may yet get to understand how it really works.
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Youāre still making excuses and blaming everyone but yourself, Carryfast. Maybe I should have closed my posts with, indeed.
Afraid I donāt know, as I never used an underdrive. Iāve read several accounts of them on here, mostly by drivers who didnāt like the gearbox at all. It might have been in Marathons or Turbostars or some other lorry I never got round to driving!
I have much older versions of the chart. The thing about this chart is that it reflects 21st cen Fullers, but we drove mid-20th century ones.
Mega true! Iāve been teaching on and off for well over 50 years and I still avoid teaching on my wits like the plague. My modus operandi is: always have a plan, even if you donāt stick to it.
You should be aware that the 15-sp Fuller was commonplace here in UK in the '60s, '70s and '80s. Most 6x4s with Fullers had the 15-sp option. Crusaders is a good example. The 4x2s and lightweight 6x4s had 9-sp 'boxes whilst the rest had 15-sp. Same with Scammell S21 T45s.
So your probably in the same situation as me, pull out an old lesson plan, blow the dust off it an check for updated information then into it, all the time moaning aboutthe prep time. 
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Maybe I should have closed my posts with, indeed.
Or to be fair
Sorry mate, Iāve lead you astray. The 13 is the exception. If you do it to a 13, it ends up as a double overdrive. Overdrive as in the 9, then overdriving the overdrive with the splitter.
What exactly should I be āblamingā myself for ?.
Regarding something which Iāve never seen let alone driven and which there is as much incorrect information and descriptions, as there are correct ones, by those who have.