Livin' large in the Ozark mountains of western Arkansas
Shifting an 18-speed
I've always wondered when driving a rig with an 18 speed transmission does the driver have to go through all 18 gears or is he allowed to skip several depending on the load? When I was driving (never drove anything other than a ten speed) I always started out in second or third and went all the way up through ten and never skipped any of them. If a driver has to split and shift all the way up through 18 he's gonna be busy! 8)
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Drive it like an 8 speed, unless you need to split. If you have enough HP, start with the splitter in OD in 1st (not low) and go 1-3-4-5-6-7-8. or splitter in direct , 2-4-5-6-7-8- 8od. No need to use them all.
I have noticed significantly improved MPG if you hit at least all of them on the top half. Start at 2nd empty and row thru em'. There is a reason it has 18 holes.
Driving it like an 8speed just burns fuel as you over rev just to grab the next hole or unnecessarily lug it down. If it is a cat for instance, it gives you the opportunity to keep the motor in the sweet spot of like 1200-1400 rpm's
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Just like with all trannies, the "lay of the land" and how much weight you are trying to get moving determines what type of shifting you should do. I will usually just shift my 13 as a 9 speed unless starting uphill or I have a lot of weight in the box. I usually will have the splitter on the low side while doing this, which will have me in 12 in the last hole, then kick the splitter to high side when I get rolling good on the highway. If the pull is hard, no doubt, I will go thru all of them. A high percentage of the time, the only split I will do is from 13 to 12 when working into an uphill grade.
A 15 or an 18 is really no different. Shift the 15 like a 10 (which it is without the splits) or an 18 like a 9 (also, which it is without the splits). Where they come into their own is running hills with heavy loads.
The new "auto" 13's and 18's will go thru all the gears. I have no problem with that. I just don't desire shifting every 200 RPM's on a manual unless I have to. Besides, on a downhill takeoff, I will skip shift anyway. Heck, you can even get the Autoshifts to "skip" shift if that is your thing.
Given all of this, most carriers won't spec these types of trannys in company trucks because the trannies are not very forgiving. You screw up shifting/splitting them, then you will find yourself on the side of the road without anything. They can be tempermental at best. There is a real place for them, but the 9's and 10's most company trucks have will take a lot more driver abuse.
I will concede that you might get slightly better fuel mileage keeping the RPM's in the 1200-1400 range as much as you can, but getting into the top hole as quickly as possible then maintaining a reasonable speed to keep it in the 'sweet' spot will do just fine in most cases. The length of time you spend going thru all the gears as opposed to into the highest gear for what you are doing will not benefit you a significant fuel savings. 25 years of driving with nearly a 7 mpg average since 1995 has taught me that.
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I have an 18 speed Mack. I do full gear shifts on the low side unless I'm on a hill, and split the gears on the high side when loaded. If unloaded, I usually do full gear shifts on the high side. I guess you can say that I'm skipping gears doing a full gear shift since, technically, I am skipping the gear that would come if I moved the splitter. However, I rarely skip gear HOLES as that would mean I'm actually skipping two or three gears! :shock:
you might get slightly better fuel mileage keeping the RPM's in the 1200-1400 range
The thing about Macks is they don't like low RPM's. When I bought this truck, I was told by numerous people that Mack engines like to be operated up around the 1600 - 2000 RPM range. :shock: As an OTR driver, I just cannot allow myself to run up the RPMs that high, but I have noticed that the engine (which is an '01 E-Tech 460hp) seems to perform better at the higher RPM instead of the lower RPM, although I keep it in the 1100 - 1600 range when shifting and cruising. The only negative about that, though, is that it tends to get a little hot with the lower RPM's.
I'm legal to 90,000 and we try to run as close to that as possible. Yesterday my loads were all within 100# of the limit. That was hauling base rock and it means the loader, even with bucket scales will sometimes put you a few hundred over and I climb on top and shovel it off and then go back on the pit scales to check axles and total. Pretty much as eplurubus said, with a heavy load and say climbing out a steep quarry road I may split the bottom half, but generally I only split the top and when it's empty I take full gears and even skip one here and there. Our company bought 23 new 2007 Pete's and they spec'd 13 speeds. I like my older truck because it doesn't have that 2007 emissions thing and my old CAT engine has lots of power.
Have any of you guys tried neutral-shifting while splitting, with your 18-speeds ?
VERY BAD idea Graymist, you can tear the splitter apart...PRE-SELECT all shifts, both range & splitter.
Interesting that you should say that, Kat. I, personally, have tried to do it a few times, with an empty single trailer & never with a super b, and ended up grinding the gears horribly, and that was the end.
I was told about this technique by one of our senior guys who does a lot of cycloning in the bush. Apparently, as per him, that's the way all the guys in the bush shift gears, in order to ensure that the gear never slips, once it's shifted into a selected position, especially in winter.