Model number for 18 speed single overdrive trasmission

That can result in fuel economy improvements
of up to one or two percent versus a comparable overdrive​

specification.

Thats off the Eaton link you provided . I agree with that statement. It can (meaning it might) gain a percent or two. Which works out to, if your driving a 7.5 mpg truck to, a .075 to .15 mpg difference MAYBE. And then only if your running 85-90% in top gear and not driving in hills. If your driving in hills according to the Eaton site an OD trans would do better.
According to Eaton's numbers you MIGHT save 1000 bucks a year. I think the Carl in the article will be along time getting his money back on changing the rear ratio. Even if you use the number that may have been quoted from an Eaton engineer at 3% that is still only half of what Bruce is saying with his half mile per gallon.
If your specing a truck form the start your not going to be out the expense of chaging your rear ratio. So it might benifit you. But I think most drivers that run all 48 would not see much of a gain and could see a loss in mileage.
Thats what great about being an O/O with money to buy a new truck. You can make it like you want it.
On a side note one of the things that really bugs me about Bruce is he always giving a name or talking about a specific truck and saying we are going to be reporting more about this build up or this mod. You never hear about it again. When he talks about a past success its always very vague. He says we worked on this or that truck and its getting this many mpgs better. But he doesnt give names or talk specifics about truck. I dont read all his articles so he might and I just dont see it.

 

You don't buy the idea. I am not going to convince you on it. Go the direction you feel best, I will do the same. I have experience with these type of setups and I will continue to use them. That is the great thing, there are so many choices we can pick from. You are not the first or the last to poo poo this idea.

True that outfits like Mesilla Valley Transport and Wally World are not using 18's, but they are using 10 directs with 2.64's and even 2.47's and having fleet average mpgs in the 8's running 48 states (yes, pulling the hills) with emission equipped engines. My running an 18 just gives me a little bit of an edge over the 10 in being able to do splits all the way down. And a pre-emission engine makes the package just that much better.

 

I like the set up this company runs and I was thinking converting my 98' Pete 379 to single drive axle with 2.64 differential. I asked around and looks like nobody can come up with the used axle that would fit Pete's Low Air Leaf suspension and accommodate a 2.64 locking differential. Just thought that someone on this forum could point me where to look............

 

That 12% number is total driveline loss. In direct gear, the losses in a transmission are not load (%) based, but merely a fixed loss from the churning of oil by gears. It varies only with speed, not power throughput, as in direct a transmission acts like a solid shaft.

Also, the RTLO B-models are not technically double-overs; only the main box is in overdrive in 13/18 gear. In 12/17, the main is in OD and the aux is in underdrive.

More on that 30% below...

Agreed, direct is the lowest loss option available.

While there is some HP loss going through any gearset, I think the mistake here is assuming that the overdrive is reducing the HP. It is not. It reduces the torque, not the HP. If you run 2000 ft-lb and 400hp through a 2:1 reduction, the output is roughly 4000ft-lb and still 400 hp. Say you put that 2000 ft-lb and 400 hp through a .75 overdrive; output is now 1500 ft-lb but still 400 hp. Gearsets change the force available, but don't change the total work available from the power source.

Oh snap! Sorry Cowpie, I let the nerd pop out! If you change power to torque in your quotes, they are correct. And since torque is what effects acceleration, it's what we care about. Here's a fairly decent explanation of how the torque/hp relationship effects performance: HP v. Torque

 

Brain fart but that means I'd have to have one first right.

 

Talk about a GREAT thread, and then...... it just stops????? Really needed the logical on the road experience and mathematical combination ending on this thread. Am ordering a 579 with either a 500/1850 isx or a 550 with an 18 speed. I run 70 and pull WIDE loads up to 20' but usually 14' area is the norm so there is MASSIVE air resistance. Was thinking of 2.64 myself for 70 mph at 1500 rpm in 16th ( direct drive ), but am very nervous about ending up with a dog of a truck that constantly has to be down shifted on every hill or big head wind. Any thoughts?

 

2.64 with low pro rubber is around 66 mph at 1500 rpm. 62 at 1400 rpm. I have never found hills or wind to be any more of a problem running 2.64 in direct as opposed to running something like 3.55 in double over. Now, for the speed I want to run, and the engine I have (Detroit 12.7 60), 2.79 would have given me a little extra edge, but the 2.64's are doing the job just fine. I primarily run my 18 speed in 16th (direct) and can pull right along with everyone else, and many times actually out pull them on hills. All depends on engine, tranny, rear end combinations. Only those who have never tried a setup this way will seem to have a cow over using it. I have very good low end grunt. Now, i will concede that "getting out of the start gate" is a little slower than, say, with a rear ratio in the 3.55 range, but not that much. And face it, I am driving a truck and trying for max mpg, not cruising the town on Saturday night with some girl with me and trying to impress everyone how fast I can "get a wheel" at the light. What I may lose in getting up to road speed quickly is more than made up for in better mpg and cooler running transmission.

Would I use this setup for pulling an over gross load of grain out of a soft cornfield? Probably not. But then, that is not what I am doing with the truck. If one is going to have extreme pulling conditions like grain out of the field, hauling rocks out of the quarry, etc, then they might not want to run a tall ratio. But if one's operation will allow it, they will do much better overall if they can stay out of the overdrives. Some would say, "then why not go with the 10 speed direct?". For me, the answer would be "because I have 16 gears from which to choose and not just 10, and my rpm spreads on shifts are tighter". And the 10 direct is not offered in a torque rating that I need. The heavier weight of the 18 in my truck was a non issue. I can still put 2000 lb more in the box than any of the company trucks at my carrier with their 10 speeds. But then, I do not have all the SCR/DPF stuff those guys have either.

 

Thanks for the detailed info Cowpie. It really is appreciated.

 

Have you guys ever looked into the 2 speed rears? That seems like it would be the best of both worlds. Super low hole AND super mileage in direct?

 

Funny, I have a '86 359 pete with b model cat, a 5&4 both OD trans and 3.70 rears, gets 5 mpg on a good day