Rear ends and transmission compatabilities

You don't have to dump the rear end ratio! I am running an 18 speed double over combined with 2.64 rears, running in 16th direct at normal road speeds. The 2.79 you have would do just fine with a 13 or 18 and run it in direct. According to the Senior Engineer at Eaton, you gain roughly 3% efficiency by running in direct, and the tranny runs cooler. I have pulled close to 80K on some real challenging hills, on two lane roads, and have never had the least problem with my 18 and 2.64's. And my fuel mileage has averaged in the mid 7's since I bought the truck in August.

You would have a great combination for any speed you needed to run. If you needed to step it up, you could go into the overdrive with those 2.79's and run at a good clip with lower engine rpm. But if you feel more comfortable with a lower rear end ratio, 3.25's would be equal in the first overdrive on road speed as your 2.79's in direct drive. That would be a stellar combination also, and you would still have one gear up for higher road speeds if needed. At least running in the first overdrive would not be as parasitic as running in double over with something like 3.55 or 3.70.

Regarding your ECM if you need one, there are a lot of outfits that rebuild ECM's for a reasonable price and would take yours in exchange. A lot cheaper than going to Cummins for one.

 

Don't worry about too little torque rating. We used to run 800 to 1000 horsepower through old 9513 (950 lb/ft) transmissions, with out problems. Now, you did have to treat the throttle like your nut sack was stuck under it, but we still raced up the big hills.
A 525 Cummins is rated at 1850 lb/ft and a 460 Cummins is only rated at 1650 lb/ft.

 

well you have the same issue i do. i have a 500 detroit with a direct 10 and 3.08 rears. THE ONLY THING YOU CAN DO IS CHANGE ALL REARS AND TRANNY, why, if you put 13 or 15 o 18 or even a normal 10 od you will not have any power in the top side. you will have a 150mph truck however. if you want to fix this go with a 13 . i prefer eaton(softer and smoother) with 3:55 or 3:73 you will get alittle better power with the half gear however those gears are not power gears. if you really want power go with 3:93 but you will have to slow down or mpg will drop. i am working on the swap now on my truck. my buddy has a 500 with a super ten 3:55 at 70mph he is only running 1400rpm with 11r 4.5 thats another option if you have tall rubber go to low pro 22.5 have to recal speedo but the will improve power also but dont and i mean dont put a od tranny in with your gears or other gears with your tranny neither will work you will have all speed or all power at 45 mph top end. i already tried....lol

 

But you showed the common misconception others have shown... you seem to think that one has to use those overdrives. Why? The same idea that I do not have to use the overdrives (and I don't by the way), is the same for the bottom side of things when one has a shorter rear end like a 3.55. They do not use each and every gear on the bottom all the time, my situation with using 2.64's is the opposite, I use the bottoms more and do not ever use the overdrives. According to those that are more knowledgable about gearing than we are, they are on the record as stating that upwards of 40-60 hp or more (and corresponding torque) is lost in the overdrives and not making it to the rear wheels, compared to running in direct drive.

I am running a 500hp DDEC IV Series 60 with an 18 spd and 2.64 rears. In 16th (direct) at 1400 rpm I am at 62-63 mph. At 1500 rpm, I am at 66 mph. That is usually the speed range where I keep my speed at. If I wanted to step it up, and was light or empty, I could go up a gear into the first overdrive (17th) and move right along at a relatively low RPM. As for start ability, no problem. And my mpg has averaged in the mid 7's. I hand calculate my mpg at each fillup and have never had a mpg less than 6.9 with this truck. I don't even have a mpg readout on the dash to show what the ECM is showing. I run a lot of two lane, hilly, curvy roads with a fair amount of weight in the box, and I have not had one issue with that tall gearing with the 18. Granny gear in an 18 will give a solid start on all the hardest pulls with those rears if needed. I have only had to use low a handful of times. And many time I even skip shift on the low side.

We have become accustomed to shorter rear end ratios and overdrives since we went to the newer low rpm engines compared to the old 2 stroke Detroits and such. Meritor and Detroit are now putting out rears with very tall rear ratios like 2.47 to match up direct drive and low rpm engines. And it is working. Now, maybe running something like a 2.64 or 2.79 will cause brain cramp for some, but then they could go with something like 3.08 or 3.25 and use only the first overdrive (12 in a 13, 17 in an 18 ). That will be far more efficient than using the double over, and you still have a gear left if you need to put a wiggle in your run.

For serious heavy haul, I would most likely not go with something like 2.64's. But for most of what passes for highway trucking, it would work just fine. As opposed to theoretical ideas about such things, I have first hand experience it works just fine all the way up to 80K lb on any hard or firm surface road. I live down 6 miles of hilly gravel road that can get quite muddy when the ice thaws or we get a serious couple days of rain. The truck, loaded, goes home each weekend. I pulled 46K of paper over I-540 and Hwy 71 from Ft. Smith to Joplin and stayed with or beat almost every other truck up the hills. And when I fueled north of Joplin, I got a 7.4 mpg. So it does work.

 

yea it works and your paying more for that 18 speed to not use the gears why not just stay with the origanal tranny. point is for it to be right you have to change your rears and tranny. otherwise your throwing money out the window for the same gear set with extra non usable gears. as for your routing thats all flat land in my books as i run pa wv and also run out to washington state. like my grandfather said if your going to do something do it right not half #####.

OP this is from my rear end and tranny shop. he says your best idea would be 3:55 rears with a 13 speed tranny. this will give you good pulling power while keeping your rpms down in OD and allow proper use of the tranny. He also said that most trannys the high side gears other than the final are a softer gear designed for take off not long crusing and that long term running could cook the gear and create hgiher op temps.

What you do is in the end your call. if i where you i woud call some shops and talk with them. if your going to put out that much money for a tranny it would suck to 1 not be able to use all the gears your paying for 2 have it go out from inproper use. good luck

 

And if I had a 13 or an 18 with rears like 3.55, I would be paying to not use all the gears on the low side. So how is your point valid? So, no, I am not throwing money away. I needed a 13 or an 18 to do what I wanted and handle the torque. No direct 10 is rated for 1750 or more torque. And I wanted to run in direct drive, which is more efficient than overdrives and transmission shows it by running cooler than it would in overdrive. So, I may be paying for two gears on the top side I am not using, but I still got my monies worth. I so I compensate for using 1 or 2 more gears on the bottom in real tough pulls. It is 6 of one, half a dozen of the other. But one advantage of having a setup like mine.... I will never have to rap out the engine to do anything. I will always have a gear higher to go and keep the engine in the sweet spot. With something like 3.55's, there is nothing more to grab on top when you get outside the sweet spot of the engine. I can enjoy those nice long down grades (not steep mountain ones) where I can let the truck roll, bump it up a gear, and slide down the grade at 80 and be turning only 1300 rpm. And at the same time, I can pull a gross load from a stop on mud with ease. Versatility is the game here. So no, I have not wasted any money at all. Especially since I got the 18 for the price of a 13. Sometimes, it pays dividends to think outside the box.

Don't try to play silly truck school games here. I just pulled a gross load up highway 93 in eastern Ohio last Friday. 20 mph corners, hills, amish buggies, and all. I do one heck of a lot of two lane, curvy, hilly territory. Pulling a gross load from Ft. Smith to Joplin is not peaches and creme either on I540 and Hwy 71. Or running 151 or 61 in Wisconsin. Running bulk loads of lead across hwy 34 in western Iowa. Not to mention the myriad of county roads I traverse weekly or the 6 miles of very hilly gravel road I live down, which the load comes with me to the house each weekend. And the truck has NEVER gotten less than a hair under 7 mpg the whole time I have owned it. And that is hand calculated.... I don't have an ECM readout on the dash to show mpg.

My respects to Grandpa, but I didn't do anything half #####. You and gramps need to step into the 21st century.

 

HAHAHAHA What a crock of ####!!! I540 and US 71 is anything but flatlands....in anybodys book!!!

 

i can find spots that i would need all 13 gears if i had the correct gears with it. that just goes to show how much flat land you do run and how little hills you run. where i live and the places i run there are times i could use deep reduction to get moving up the hills. and with your setup those mild hills will have you in the low side for sure. or with the right gears you would still have to power in the top side along with good speed less shifting less shifting equals better mpg. less shifting equals less wear and tear. less shifting equals less driver wear. but than again a flat lander that does not know what a hill is would not know about these things. so yea just throw parts at your truck and save up for the tow bill when it falls apart on you...but seems every post on here you claim people are stupid for doing things the right way not the half ### way so no since in returning to hear your next line of bs