Changing rear end?

Thanks 25(2)+2. I could not remember if the overdrive transmissions and high numerical rear gears (3.73s, 3.42s etc.) took some of the stress off the transmission or the rear end with the extra leverage.

The companies probably, are now leaning more towards direct drive transmissions, as the high speed rear ends (2.64s etc.) are spinning the gears less in 2 axles, hence more efficient (lower drive line loss.)

I know that they are continually dropping the peak torque rpms, but I am not so sure if a truck running with a couple more rpms, and a little more leverage, albeit running more free, will not get just as good of mileage; but the engineers are a whole bunch smarter than me.

Given 2 trucks indentical, the driver can determine the lions share of the fuel mileage difference. I have seen as much as 30% variance between drivers. Speed, starts, and idle time. Huge money nowadays....

If I owned a trucking company, I would have some kind of fuel mileage bonus program. Both the driver and I could save money, instead of blowing it out the stacks, and paying the fuel desk the extra....

 

The newer axles being used in direct drive / tall ratio setups are using better Amboid designs instead of the older Hypoid design. The 18 spd, with 2.64 rears I have in my glider is using Meritor's new 14x axles with premium amboid design. I operate it primarily in direct drive (16th) for maximum efficiency. True, I am not using the top two gears (every once in a while I will get into 17th and step the pace up), but I have the low end grunt, and a selection of 16 gears I normally use, and a tranny that can handle far greater torque than a 10 direct ever could. some would argue "why have a transmission and not use all the gears?". I would say the same thing to someone who has a 13 or 18 with 3.70 rears. We all would not use each and every gear, each and every time. But it is nice to have just the right gear, in just the right situation whether running normal or tall rear ratios.

 

I do not see them listed now, but FR used to have 2000 ft. lb. torque 10 speeds. In direct drive, not sure. They were not much heavier than a 16 lb. 10 speed.

The issue, other than cost, and more weight with the 13 and 18 speeds, are that 40 years ago, I was told that running through the overdrive box, took about 12 HP. (Yes, I know, who is this they? lol)

But, like the new advanced rear gears mentioned, probably a lot has changed, and maybe not much loss at all. With the new lighter oils and synthetics, there is not the friction that used to be.

I can remember on a minus degree day, it took miles, to just be able to move the gear lever without fear of breaking it. Of course, about that same time, those old bias tires started rounding out, and the wheel bearing grease started to unthaw.....Tough going with an old 238, 0 torque, 2-stroke Detroit, with small injectors.......

 

Yes, there is still a parasitic loss of power to the rear wheels by running in overdrive. Nothing has changed. It does vary, by who is giving out the info, on how much is lost, but the fact remains that running in overdrives, there is less power actually making it to the wheels than in direct drive and above a 1 to 1. The senior engineer at Eaton corp is on record at the 2011 MATS as saying that there is upward of a 4% loss in overdrives compared to direct. Eaton, in its literature, doesn't go that far, but will state that there is a 3% loss. This is for single over (roughly .86), and double over (.73 or .74) is even worse. I will admit, that overdrives have their place, just as direct drive has its place, and every situation is not the same. But most folks, would benefit by not having the speed made up for in the transmission overdrives and use a taller rear ratio and direct to attain that. Many of us have just been accustomed for so long to look at the picture one way, it is hard to change and realize that their are more efficient ways of getting the job done.

Before the mud slinging begins, I stated "most folks" would benefit. Don't throw out ideas about pulling 140K loads and how this wouldn't work "Most Folks" are not pulling heavy, OS/OD loads, so don't get ridiculous in countering my contention and show what a moron you are. I realize quite well that tall ratios with direct drive is not a one size fits all solution for every trucking situation there is. My contention is that many folks, who don't realize it, could go this route comfortably and reap benefits from doing so.

Weight of the tranny was not a factor in my decision to go with an 18. I can still comfortably put 48K in the box if I needed to before getting close to 80K gross (most I actually put in the box is a shade over 46K). I have an extremely light setup overall. Quite probably because I have no emissions devices to add the extra weight and am using aluminum housing drive axles with wide based rubber and only 100 gallon fuel tanks. Spec'ing a truck is everything.

 

Don't know what the OP is pulling or where but IMO a good general setup is a 13 speed with 3:70's and 22.50 low pro's. The easiest way to improve fuel mileage is to slow down....it really is that simple!!

 

Much as some don't like that idea, it is very hard to refute!

 

LOL, I forgot to mention it's an extremely cheap fix with an immediate ROI.........

 

You've got to figure out what your time is worth before you know if it would be a worthwhile investment. If slowing to 62 mph would get me an extra 1/2 mpg vs. running the speed limit, but it would mean putting in an extra hour every day just to get the same amount of work done, then the "ROI" isn't enough to justify slowing down. I might save $30/day in fuel, but it would cost me that extra hour.

I wouldn't fire the truck up in the morning if all I was going to make was $30/hour...so why would I put in an extra hour just to save that $30?

Of course everybody's situation is different...

 

LOL, I hear ya.....I don't work that hard anymore.......62 is my cruising speed, got 7.2mpg from L.A. to Allentown and 5 days to get there so not in any big hurry if you can't get the freight off early.

I appreciate your Herman Cain quote.....