Gordon....I probably should have prefaced a disclaimer before I went off with my explanation of shifting without using the clutch. Sometimes it's just nice to "know things" even if you never need to implement that knowledge. Funny you mention a Fuller 10 speed trans. I used to work on them. Also their later 13 speed version. Before they came out with the 10 sp, many trucks used 5 speed transmissions with an auxiliary 2 speed transmission connected behind that. This required two shift levers ! Many of these set ups had double disc clutches as well. Starting with the flywheel you then had a clutch friction disc, then a floating flywheel, then another friction disc, then the pressure plate. From there it went into the transmission where it was directly connected to the countershaft (some people call this a "cluster gearshaft"). Up to this point ALL of it would continue to coast when the clutch was disengaged. Because of all the weight and inertia it would all slow down faster than you could shift. Not only one but Two transmissions had to be shifted causing the gears to clash (grind) and making your life miserable. The remedy was to "double clutch" the MF and keep the speed (RPM) of all that gear-train moving close to the same speed to prevent gear clash. The procedure was to disengage the clutch, shift to neutral, re-engage the clutch, then disengage the clutch and shift to the next gear. You had to do this as fast as you could. In my explanation with a 5 speed main box and a two speed auxiliary trans, the tough shift was from 5 to 6 because you had to shift the 5 speed back to first and the aux to second all while you were double clutching !
The strongest and simplest truck transmission I ever worked on was in a Mack with a Maxidyne turbocharged-aftercooled 6 cylinder engine. TONS of Torque at 1500 RPM ! That transmission had the main gearshaft surrounded by three countershafts in order to handle the torque. A very simple and brutally strong transmission ! But occasionally the torque would crack the gear case even then. It takes a lot of heavy-duty equipment to move 80,000 pounds down the road !
Allison 12 speed automatics in a Peterbuilt is another story..........Bruce