13 speed??

My guess would be for heavy heavy loads... like a Michigan gravel train, which can gross 164,000 pounds. You might need a few more gears to get something like that rolling. Coincidently, 18 speed tranny's are popular in Michigan too.

 

I haven't driven a 13 speed in a long time... and if memory serves me right, there are a few ways to shift it. Basically though, you can split the high side gears. Run through the pattern on the low side, select the high range and low side on the splitter, and shift to where 7th gear would be on a 10 speed... flip the splitter to high, leave the stick where it is and let off the throttle momentarily—it'll shift to the next gear. then low side of the splitter... select the next gear with the stick... split... again.

 

Everything I've driven since about 1995 has had a ten speed in it. You're correct... I don't see any reason for a 13 speed in an 80k OTR truck.

 

it brings your shift points closer together

with a 10 speed you start every gear lugging, and by the time you shift your about wrapped out

with a 13, when you split the top half your rpms only change by about 300

with an 18 you can split both bottom and top sides, still keeping your rpm change to about 300

basicly it just gives you better economy by keeping in the power band, and helps keep speed when pulling a grade by keeping you in the pwer band

 

shift pattern is

r 1 3
- bottom side
lo 2 4


r 5h/l 7h/l
- top side
lo 6h/l 8h/l

once from into the topside, just split from lo to high, back to lo in between gears

 

I prefer an 18 but the 13 is a good tranny. You get better fuel mileage when you don't have to rev her way up in every gear. I like the 18 for the extra low reverse gear.

I have the old style straight but gear 13 in my truck. load as all get out in overdrive. I will eventually swap it out for a new 18 double over.

 

Your question about procedure was answered earlier, and there is no reason why 10 isn't enough. A 13 speed tranny is simply better. It's more effecient in the realm of trucking, both on mountain terrain and also in the form of fuel economy. Big companies likely go with 10 speeds for cost reasons I'm guessing. As far as being too complex or unnecessary, no not at all. Very simple really. I generally pull loads grossing about 102,000 and use a 13 speed. If I were doing any more mountain driving than I currently do, or if I were running smaller horsepower I would prefer an 18 speed. Right now with the horsepower I have, and the weights I haul the 13 speed is the best option. Just as there are differn't trailers for diff. kinds of freight, the transmission is no differn't.