Rear ends and transmission compatabilities

SO that was you slowing me up on 93 the other day!!!!

 

carrkool: Look at these two websites
http://www.vibratesoftware.com/html_help/2011/Eaton_Fuller/Transmissions/eaton_13speed_trans.htm
above for 13 speed Eaton ratios, for each gear

below link for 18 speed Eaton ratios, for each gear
http://www.vibratesoftware.com/html_help/2011/Eaton_Fuller/Transmissions/eaton_18speed_trans.htm

Now, even if you say you know places you need all of your 13 gears, take a gander at the first gear of both the 13 and the 18. The 13 speed is only 10.40 while the 18 speed is 14.4. Also notice how the top 3 gears, 11,12,13 and 16,17,18, are all ratios of 1.00, 0.86, 0.73. Cowpie1 has the ultimate setup for hauling 80k gross on mostly paved roads. This setup allows him to use the direct drive gear, 16th, which is proving to save $$ in fuel. The slow crawl start is not effected, just he may have to start out in the lowest gear to get it going. Also, having a high enough top speed which is rarely to never used, allows for the case where if you really need (want?) to move on down the road that capability is there also. This is the setup I would like to have someday, except in a W900L glider. But I would take it one step further. I'd MB everything.

 

Seems like they need to make a 12speed direct trans. That would be the best of both the 10 + 18 speed transmissions .

I do 100k to 110k gross on every load. All the old timers run 18 speeds with 4.10 rears, and 24.5 tall tires. They think I'm nuts for trying 3.73 rears. For what I do I would not go any higher (lower numbers) on the rears. I do use 1st high split to start off when loaded all the time. And fuel milage blows.

 

your 3.73s do just fine dont they? i run 3.70s with an 18 grossing average of 140000 and stay with the boys runnin 4.10s sometime passin them and yes fuel mpg does blow. it will with this kind of weight. 3.6 to 4.2 is my average. but i dont run a stock engine either.

 

hes not getting the fuel savings you think. when you have to drop the the low side your gear ratio is causing you to burn ore fuel than if you setup to run od at 24 percent. Now i am not saying by anymeans someone needs to go with 4:11 gears but if going from a direct drive tranny with 2:79 rears you need to bump your rears up to around a 3:55 those 2:79 behind a 13 or 18 is going to drop pulling power badly as the gear ratio even running direct in the 13 or 18 is like od on a 10. getting a good gear ratio with your tranny and tires is very important but you have to mate them together. But i am not going to set here with cow and fight he does this on every post on this site if the guy decides to go with just his tranny he will see what i am talking about real quick.

 

Nothing wrong with Cowpies math or logic. I think a driver might have problems with his set up BUT not going down the road. You say "running direct in a 18 is like OD in a 10". My question to you is do you understand what your talking about? Direct is 1 to 1 does not matter what tranny it is. An OD 10 that would be 9th gear. Lets say we have truck running 1300 at 65. The motor does not know how its broken up behind it. Weather its through the gears in the trans or the rears or the tire size. Its going to run the same does not matter if your running 16th or 18th to get there. Now there are slight benifits to improving the efficiency of the components like running in direct, efficient tires and such that you can save few tenths of a mile per gallon then go for it. I personaly would not build a truck like that but if I pulled a 10 direct out of truck to swap in a 18 I would not change the rears just to do it either. You need to remember that you wont be running in the top hole anymore cause if you do the truck wont pull.

 

EDIT: I started to use physics to show you Cowpie is on the right track, but I realized you already know everything and I'd just be confusing you with the facts.

And I see DL550 beat me to it!

 

Wow, carrkool. How many years did you run Alaska and the haul road like I did? And I don't know hills? Try playing around on Thompson pass in -35F weather and tell me that.

I have not fought with anyone on any post until they have attacked first. I bring up options, some of which there are always folks that will disagree with. They will attack only on a personal level, but not show any facts to back up their contentions. I have never said anyone was stupid or an idiot if they did something different than me. I show how any ideas I have suggested has worked. I have also offered alternatives even to what I am doing, if some would take the time to read what has been written in my various posts and not just see what they want to see.

In regards to the 18/13 and tall gear idea, it works for what most people do in trucking. Sure, there are situations that go on that would this would not be the ideal setup. THERE IS NO PERFECT SETUP FOR EVERYONE. But the logic is sound. Anything to reduce the time in overdrives is beneficial. The senior engineer at Eaton has shown it, and is on the record. Now they have far more experience with transmissions and engine/rear end combinations that all of us put together. I also suggested, that if loads were heavier or terrain was more of problem, then something like 3.08 or 3.25 is a good choice. That is the same as 2.64 or 2.79 respectively except in the first overdrive, which is less parasitic than double overdrive. And it would leave 1 gear up on top for days when one needs to stretch out the pace or is running empty or bobtail.

 

Yup the 3.73s are a good "compromise " for what I do. On the hwy I can run hard but I need all the gears and splits. Not so efficient I know. Some day maybe I will slow down and run 7th or 8th direct only (16th or whatever you want to call it). Just to see if I can get the fuel milage to go up. Back roads are ok. Backing up in some of our tight spots with a full load kinda sucks. This is where I could use some more gear. But if you plan your moves well, it's livable .

 

Dl550cat. Thats my point. Here is my out look on things. Why spend all that money on an 18 speed to have to run the same final gear ratio and not see any real good come from it. when in fact putting an OD tranny in place of a direct tranny is going to cause you to lose pulling power in the top side causing you to drop to the low side, put more stress on the motor trying to pull a hill with no gear power and using nothing but raw HP. If your going to do something do it right. His rear gear ratio is way to low for an od setup. even a 10speed od would be an issue with those gears. as for what eaton and them say its funny since i have been dealing with them and any tranny and rear shops trying to figure a setup for mine. which by the way is a 10 speed direct with 3.08 rears. when talking with any shop so far all have told me i have to change my gears to see anything possitive come from a bigger tranny with od. they have told me the best option for my truck with a 500 detroit tuned up is a 13od with 3:55 rears or an 18 speed with 3:43 rears since the 18 od has a higher od percentage. that setup will give me good pulling power and good highway crusing speed and keep my gearing right for proper shift points with power.