I've never heard of an Eaton Fuller 12 speed, nor am I able to find any references to one via Google. I've driven Eaton Fuller 8LL, 9 speed, 10 speed, 13 speed, and 18 speed transmissions - could you be thinking of one of these?
IIRC, Volvo marketed a proprietary 12 speed transmission, and Meritor offered a 12 speed automatic, but not Eaton Fuller.
It's the same as the shift pattern for the Eaton Fuller nine speed transmissions, albeit with additional gears on the low side. For the sake of not wanting to type out a long winded explanation, there is a related link posted - 'Eaton Fuller 18 speed shifting diagram'. Click on that link to see a visual representation of the shift pattern.
Same shift pattern as a 9 speed. Youtube has a great video straight from eaton fuller on it that would be better than me typing it.
Keep rpm between 1400 to 1600
No you cannot change a 13 to a 18 speed, however you can change a 18 speed to a 13 speed just by changing the shift knob.
No you can not, it is a different transmission. The 18 speed has a splitter for the lower range as well as high range.
Depends on whether you have the synchronised gearbox (more common in Europe) or the unsynchronised gearbox (such as an Eaton-Fuller or Rockwell).
The Eaton-Fuller and Rockwell websites should have them. Google images will be able to find images, as well.. you just put in "8LL shift diagram", "9 speed shift diagram", "10 speed shift diagram", etc.
Installation of countershafts
Either a proprietary Mack 18 speed or an Eaton-Fuller 18 speed. Various models of the Eaton-Fuller were available, from 1600 torque to 2100 torque.
Fuller Transmission shift diagrams.There are several places on or offline where you can obtain and Eaton fuller 15 speed gear shifting diagram. It depends what method you prefer. such as from your Truck dealer or a Truck Transmission Re-builder or someone who offers fuller transmission parts and service. For more information of sources online, see the Related Links section further down this page.
Grey, both on an Eaton-Fuller and a Mack 18 speed.
The ideal RPM range depends on your engine, and the speed depends on your transmission gear ratios, rear end gear ratio, and tire revolutions per mile.