best gearing for fuel consumption on a ea7/e7 470hp

[Gorilla]

Hey Everybody,

Today i drove my mack quantum for the first time and was surprised at how high it was revving in top gear (1700rpm).

It has 4.56 eaton diffs and a .73 overdrive.

I was looking at peoples opinions given it has both .86 and .73 overdrives what would your thoughts be for me to change the gearing on the diffs to 3.73?

In 18th gear (.73 overdrive) it will give me 1383 rpm

and in 17th gear (.86 overdrive) it will give me 1630rpm

and in 16th gear (1:1) it will give me 1895rpm

This is all calculated at the maximum allowed speed in australia for trucks which is 100km/hr

The way i see it is on a nice level road it will give me the best fuel efficiency as it will be thick in the maximum torque range.

On inclines i can split it to 17th gear which will kick me near the maximum hp and still within beefy torque values

Im tossing up doing this as i want to maximise my fuel efficiency and i am going to get the diffs sorted as i want to fit lockers and cross locks anyway so essentially two birds one stone.

Any thoughts?

Thanking you in advance,

Chris

[Geoff Weeks]

My advice is don't guess or take someone else's guess. Get the graph of the power torque and BSFC curves for the EXACT engine you have, then do the math to find what ratio will put you at the lowest point in the BSFC curve at the speed you want to cruise at.

 My experience is slightly different than yours, as I didn't have all the gear choices that 18 does. However after hours of pawing though the math, and plotting on graph paper, I selected the ratio that got me as close to my ideal as possible. I have never regretted the ratio choice and left me with a much more comfortable truck to drive, and upped my mileage between .75 and one full mile per gal.

 You'll need the rev's/mile of the tires you are running as well. 

Once you have it centered in the low spot on the BSFC curve, with all those splits on the top end, if the torque rise is a problem you can drop a ratio or two when you need to pull a small rise, and go all the way down to direct when pulling a steeper rise.

The factory did the hard work of plotting all this stuff, the info you can't easily get from the driver seat, so ask them for a copy.

[mrsmackpaul]

Something to consider before changing ratio is that the GCM in Australia takes into account a thing called "gradeabillity" not sure on the spelling 

But it is the ability to lift off (start on a steep hill)

Our gearing in Australia can seem ridiculous compared to the US and Europe but the GCM in Australia has this very important part of maths in it

Remember most prime movers (tractors in the U.S.) are rared for B double work were up around 70 ton (154000 lbs) GCM is pretty standard

Changing the ratio will have a effect on this 

 

Paul

[Geoff Weeks]

I think with a 18, that will not be a problem, they have a fair spread, but as I say, do the math, look at total reduction as well.

The disadvantage of the 18 is all the reduction is done up front, so the driveline has to handle it.

[mrsmackpaul]

In Australia it will definitely have a effect, the question is whether the effect is enough to change the gradeability to have a negative impact on the work that is wanted to be performed 

But I  do agree with you Geoff, do the math and work it out

There's a mob in Brisbane that will work it out at a cost and can if needed re certify the truck and replate it to provide a new GCM, this is normally only done when you want to increase the GCM from what it is plated at

You can take the truck into any authorized person anywhere in Australia and they inspect the truck to confirm it is as stated, they forward the details onto the mob in Brisbane who then issues a plate stamped with the new details to be fitted by that dealer that inspected the truck

Some dealers and truck modification specialists can also do this in house 

 

Paul 

[Geoff Weeks]

I have to remember your rules are different, here a ratio change is not something anybody but you have to know about,

If grade ability  is a problem, the 2 spd axles can extend both ends, but that will rule out lockers. One or the other but not both.

[Gorilla]

HRM, two speed axles you say, this is interesting.

I am running RS462 diffs with 4.56 ratios and am wondering what diff centre i could replace it with that will give me say 3.7 + 4.56 ratios? or 3.7 +5.2 or anything that way.  Would be VERY cool having best of both worlds.  Do you have any info on this?   I want to retain the power divider but could live without lockers.

Spoke to one diff place today and alas its australia so they didnt even attempt to use lube when they quoted me and also told me im stupid for going that low in gearing, spoke to another diff place and explained what im doing and they reakon it will work.  Now where do i find these two speed diff centres,  i want some BAD!

 

[Geoff Weeks]

Ah, bad new, I can't find a DT 462, if you had 461's you could replace the DS/RS 461 centers with DT 461 centers. Eaton numbering goes like this:

D= front tandem or tandem set

DS tandem set single speed

DT tandem set 2 spd

DC traction control single

If you had DS 461's DT sets were made. But since 2 spds have dropped from favor the latest axles didn't have 2 spds

The DS 402's (40K singles) could take DT 402's or any center in that "family", and be made into a 402 by changing the side gears to match the axle shaft.

 Same held true for the larger 46K axles.

 I don't know if the larger axle housings are the same as the smaller, with the "notch" to allow traction control or 2 spds. like the smaller housings were, the single speed housings will accept 2 spd or traction control centers.

 If you find that 461's will bolt into your 462 housings, than there is  the chance that you could get older 2 spds

the high/low ratio is always the same split, it is fixed by the planetary ratio inside.

They come in most all the same ratio's as singles do in high

so yes 3.70/5.05 or 4.11/5.61 would suit.

n 1st thing before you go on a search, is talk to Eaton rep or a knowledgeable  gear shop to tell your options on the DS462 "family". of rears.

 This is exactly what I did on my truck, replaced DS402's with DT402's I built up from cores.

[Gorilla]

51 minutes ago, Geoff Weeks said:

Ah, bad new, I can't find a DT 462, if you had 461's you could replace the DS/RS 461 centers with DT 461 centers. Eaton numbering goes like this:

D= front tandem or tandem set

DS tandem set single speed

DT tandem set 2 spd

DC traction control single

If you had DS 461's DT sets were made. But since 2 spds have dropped from favor the latest axles didn't have 2 spds

The DS 402's (40K singles) could take DT 402's or any center in that "family", and be made into a 402 by changing the side gears to match the axle shaft.

 Same held true for the larger 46K axles.

 I don't know if the larger axle housings are the same as the smaller, with the "notch" to allow traction control or 2 spds. like the smaller housings were, the single speed housings will accept 2 spd or traction control centers.

 If you find that 461's will bolt into your 462 housings, than there is  the chance that you could get older 2 spds

the high/low ratio is always the same split, it is fixed by the planetary ratio inside.

They come in most all the same ratio's as singles do in high

so yes 3.70/5.05 or 4.11/5.61 would suit.

n 1st thing before you go on a search, is talk to Eaton rep or a knowledgeable  gear shop to tell your options on the DS462 "family". of rears.

 This is exactly what I did on my truck, replaced DS402's with DT402's I built up from cores.

Interesting, im under the impression that the 462 is a newer revision of the 461 as the pinions etc are the same and the rebuild kits suit 461,462 and 463.  So yeh ill speak to a rebuild place and see what they think as maybe it might not even cost more as a rebuild kit is the same and instead of getting new ratios installed ill just put a rebuild kit through it before i get it installed    This would give me the best of both worlds    btw what ratios are you running?  and what motor +  whats your gearbox final drive ratios

 

[Geoff Weeks]

Eaton use family of gear sets. The 402's are the same center section as a 341's  The 402's have a weight cap of 40K while the 341's are 34K, the only difference is the side gears that the axle spline mate into. As you would expect as the weight rating goes up, the size of the axle 1/2 shaft does also.

For my purposes, this means I could use any 2 spd core from early DT340's to the latest DT402's, When I re ratioed  to my chosen ratio I installed 402 side gears and then just popped the 2 spd center in place of the single 3.90's I removed.

 You can not build a 2 spd out of a single spd core, the carrier casting is not made the same. You need 2 spd cores to build a 2 spd axle. 

 I went with 2spds because I could find old cores cheaper than modern single speed. As it turned out I had a 2 spd (17200) in  a single axle tractor that I could re ratio and used in my "rear hole". I just needed a front core from a tandem to re ratio and I was set. I found a DT341 core and made the swap

I went from 3.90's to 4.11/5.61 (? I don't remember the exact low ratio, could look it up) and gained .75-1.00 MPG. I had a 425hp 3406 and a RTO14615 in front so same .73 O/D you do, on 10.00x 20 rubber.

 So to recap, you need some 2 spd cores, and the rear rear is the same as use in SOME single rear trucks. 

The difference between  rear diff "families" is the lighter (34K-40K) use either 16" or 16.5" ring gear and the larger use (I think?) 17" or 18" ring gear, obviously the houseing and center casting are different to accommodate the larger gears. The same center section was used in 46 48 and 56  (46k 48k and 56K) rears with differing side gears in each. I think the 18200 single rear would be of the same "family" as your 46's.

 The question you have to answer is if you housings will accept a 2 spd center? For example: the  bolt circle and housing size is the same on a set of IHC 472's and Eaton 402, and you would think you could sub in a Eaton but the area around the axle line is notched out to allow the shift fork on DT and DC axle models on an Eaton housing, it is not on the IHC.  I don't know if all Eaton housing are built like this. Mine were in a Marmon, a low production truck, so I would guess Marmon would order only one Eaton housing for use in all Eaton rear trucks. They would only need to stock one, and drop in whatever center the build sheet called for.

 I have heard conflicting info from yards and builders as to whether all Eaton housings are provided with the cut-out or not. Some say yes, other say no. Mine were. In your case, where I don't see a 2 spd 462, I would check your housing before ordering a set of cores. On the housing at the center line where the axle goes there are two bolts (top and bottom) and the axle center line passed between them. on the rear rear left and front rear right, the opening will have a [  or the right of front and ] on left of the rear instead of being (   ) {equal on both sides}  in other word it will look like [   ) on the front and (    ] on the rear. You can only see this with the center section out.

 If this is not clear I can try and get some pic's of a set of Eaton 402 housings.

[Gorilla]

1 hour ago, Geoff Weeks said:

Eaton use family of gear sets. The 402's are the same center section as a 341's  The 402's have a weight cap of 40K while the 341's are 34K, the only difference is the side gears that the axle spline mate into. As you would expect as the weight rating goes up, the size of the axle 1/2 shaft does also.

For my purposes, this means I could use any 2 spd core from early DT340's to the latest DT402's, When I re ratioed  to my chosen ratio I installed 402 side gears and then just popped the 2 spd center in place of the single 3.90's I removed.

 You can not build a 2 spd out of a single spd core, the carrier casting is not made the same. You need 2 spd cores to build a 2 spd axle. 

 I went with 2spds because I could find old cores cheaper than modern single speed. As it turned out I had a 2 spd (17200) in  a single axle tractor that I could re ratio and used in my "rear hole". I just needed a front core from a tandem to re ratio and I was set. I found a DT341 core and made the swap

I went from 3.90's to 4.11/5.61 (? I don't remember the exact low ratio, could look it up) and gained .75-1.00 MPG. I had a 425hp 3406 and a RTO14615 in front so same .73 O/D you do, on 10.00x 20 rubber.

 So to recap, you need some 2 spd cores, and the rear rear is the same as use in SOME single rear trucks. 

The difference between  rear diff "families" is the lighter (34K-40K) use either 16" or 16.5" ring gear and the larger use (I think?) 17" or 18" ring gear, obviously the houseing and center casting are different to accommodate the larger gears. The same center section was used in 46 48 and 56  (46k 48k and 56K) rears with differing side gears in each. I think the 18200 single rear would be of the same "family" as your 46's.

 The question you have to answer is if you housings will accept a 2 spd center? For example: the  bolt circle and housing size is the same on a set of IHC 472's and Eaton 402, and you would think you could sub in a Eaton but the area around the axle line is notched out to allow the shift fork on DT and DC axle models on an Eaton housing, it is not on the IHC.  I don't know if all Eaton housing are built like this. Mine were in a Marmon, a low production truck, so I would guess Marmon would order only one Eaton housing for use in all Eaton rear trucks. They would only need to stock one, and drop in whatever center the build sheet called for.

 I have heard conflicting info from yards and builders as to whether all Eaton housings are provided with the cut-out or not. Some say yes, other say no. Mine were. In your case, where I don't see a 2 spd 462, I would check your housing before ordering a set of cores. On the housing at the center line where the axle goes there are two bolts (top and bottom) and the axle center line passed between them. on the rear rear left and front rear right, the opening will have a [  or the right of front and ] on left of the rear instead of being (   ) {equal on both sides}  in other word it will look like [   ) on the front and (    ] on the rear. You can only see this with the center section out.

 If this is not clear I can try and get some pic's of a set of Eaton 402 housings.

your fairly clear, i think you misunderstood me, as im thinking weather i can find some two speed 461 housings in the right ratio with good ring and pinion and pay a diff mob to throw a rebuild kit through it then fit it to my truck.  Part of the cost will be offset as ill sell my original diffs which are in good condition.  Sadly i spoke with a diff rebuilding place today and for two reco diffs to change over they wanted 15k aud inc fitting but to me that sounds insane given my cores are not in bad condition and all i want is a ratio swap.  Tomorrow ill call the other diff builder i spoke to and see if he believes the 461 two speed carrier will go into my axle, if it does then the hunt will begin.  Part of me is thinking i can swap the diff centers myself because ive done axles and axle bearings myself without a problem and i can weld up a A frame or even use my engine hoist.  Doesnt seem any more difficult then single handedly doing a gearbox swap on a 4wd with a transfer case (which ive done without problem).  In Australia the labor charges are crazy stupid expensive and a lot of truckies go broke because of them......i do most of my own work but dont want to screw around with shims and alignments in building diff centres because there is a bit of black magic that happens there that you cant learn without years of experience.

 

[Gorilla]

Just realized, my truck will effectively be a 36 speed with a 2 speed diff hahahahaha

Edited August 28, 2023 by Gorilla

[Geoff Weeks]

No, it is not hard, done several myself. Lifting from the top  (if you can) is better than dropping out the bottom. 

Neat thing about 2spd gear sets, is the ring gear is bolted to the carrier, so if you are comfortable setting up final drives, it is an easy job to change ratios. You have the selective fit on the pinion bearing to deal with and the press on spigot bearing on the end  of  the pinion, but all those part can fit in you boot or footwell of a car and taken to someone if you don't have the equipment to do that part of the job. Single speeds often come with the ring gear riveted to the carrier, you have to drill out and install with a bolt kit in the field. OEM use a big rivet "squeezer", but replacements are done with bolts.

 Make much more sense to re-use you housings if at all possible, not only do you not need to find housings that are set up for your suspension, none of the wheel end/ brake parts need to be touched. Just zip out the old and replace with the new, even the 1/2 shafts are re useable.

 A note on ratios, the split between low and high is almost exactly the same as dropping one gear stick position (not splitter), so many of the potential ratio's will overlap, two way to arrive at the same thing!

 I use mine in low for starting, than run up through the gears to top gear, than switch to high for the last two ratios. When climbing a hill it is the reverse, drop two, downshift and run the hill in direct-low. Keeps the heat out of the trans while pulling hard.

Edited August 28, 2023 by Geoff Weeks

[Geoff Weeks]

Here is a pic of the 402 housings and the notch I am talking about. You can clearly see the cut-out on the right side for the shift fork Edit: left side of photo, right side of front housing. You are looking at front housing faceing toward the rear of the truck.

Edited August 29, 2023 by Geoff Weeks

[67RModel]

2 hours ago, Geoff Weeks said:

 I use mine in low for starting, than run up through the gears to top gear, than switch to high for the last two ratios. When climbing a hill it is the reverse, drop two, downshift and run the hill in direct-low. Keeps the heat out of the trans while pulling hard.

You seem to know a lot about two speed diffs. I always thought they should be much more prevalent than they are. I guess with modern engines and auto transmissions they have become almost non existent in new trucks. Are Eaton axles and Dana Spicer axles synonymous? You keep saying Eaton but DT series axles I thought were Dana Spicer. Did one buy the other and they are all the same now? How does downshifting the two speed work? Do you flip the switch while the trans is still in gear and then lift of the throttle to break torque then lay into the throttle to raise rpms until it engages? I drove many single axle 5+2 gasser dump trucks that were like that. They had Eaton "Double Duty" electric shift rear ends. It was actually a very handy setup. They were real clunky going from the high side to the low side (downshifting) the axle. I just wonder if air shift two speed tandems are the same.

[Geoff Weeks]

Air shift is my favorite, Yeah, push the button down, while under load, let up or step briefly on the clutch and it down shifts. Vacuum is my 2nd with electric being last on the list.

I have the Marmon with air shift and two K-7's with vacuum.  Marmon has a 3406, the K-7's are 269 gassers.

 Like anything else, a little time in, it becomes second nature.

 Eaton held the patent of the planetary gearing in the 2 spds, Timken, Detroit, Rocknwell also made 2spd's but they were a double reduction units that either hung off the front or on top like a Mack. The advantage of Eaton's design is the whole thing fit inside the ring gear, the disadvatage was you were limited in what planetary ratios would fit inside the ring gear, so most often they are around .73 between low and high.

 Eaton, Dana and Spicer rears are all the same company (Dana Holdings Corp) now, Spicer sold of the trans business to TTC, because Roadranger was part of Eaton, so they would almost be a monopoly if both Eaton/Roadranger and Spicer heavy transmissions were one and the same company.

 My air shift are electric over air. Air solenoid controls air pressure to the two shift cyl on the axles. You could use an air knob on the stick, but you still need an electrical signal to the speedo or speedo adapter to keep the speedo reading correctly in both ranges. Since I needed an electric signal anyway, I went with the typical "red knob" on the side of the trans stick. Also I had a 15 speed trans that needed its own shift knob. I could have made it all air, but it would have been a rats nest of air line coming up the stick.

 I agree, they should be used more, and if I ever had the chance to spec a truck the way I like, they would be top on the list. Doing more of the reduction at the rear, means you don't need as heavy a driveline, like you do when most the reduction is done at the trans. Like a two or three stick, you can't be in a hurry, but once you learn them, they are great.

[Gorilla]

That notch seems like nothing problematic if you have a grinder  

Been doing a lot of thinking and given i have 18 speeds i really see no point of a two speed differential.

Do you guys have a lead as to who i can buy the diffs centers in the usa?   just want some 3.7 462/461 with power divider, obviously one ds p and one rs

Also had a good look at whats involved in changing the diff centre and have decided im gonna do it myself.

 

Edited August 29, 2023 by Gorilla

[Geoff Weeks]

1st I'd make sure the 462 is interchangeable with a 461. In lighter diffs the 402 is not interchangeable with the 404. 

2nd 46x and larger are less common here, but still a fair number. The adv road tractor has 40K rears, dump and off road will uprate to 46K

 That said I look to the major yards and gear shops.

 No idea what it would take to get some of these yard to ship down under.

[Gorilla]

4 minutes ago, Geoff Weeks said:

1st I'd make sure the 462 is interchangeable with a 461. In lighter diffs the 402 is not interchangeable with the 404. 

2nd 46x and larger are less common here, but still a fair number. The adv road tractor has 40K rears, dump and off road will uprate to 46K

 That said I look to the major yards and gear shops.

 No idea what it would take to get some of these yard to ship down under.

Oh yes im going to make sure of the compatibility of the 462 and 461 although all the parts ive seen listed for the 462 list the 461,462 and 463 as that part fitting thus my assumption that its just a different model number for the same part (maybe different stamp to coincide with truck manufacturer?).  HRM so 46 was not a common diff?   Strange this model mack would come with it factory.  As for shipping, yeh ive contacted a few mobs and will see what they come back with.  Do you know of any place you could recommend?   I check on air freight and it would still be much cheaper then getting one local.                                                                        

[Geoff Weeks]

Well, different things are "common" in different markets. 24" rubber is or was common down under and in the middle east but was not common outside the NY/NJ area in the US. 

46K rears are common in dumpers but not road tractors in the US. You could spec whatever you wanted, but common spec for a road tractor was 34K for a long time then 38 and now 40K. Often when you go bigger on capacity you are required to go bigger on brakes as well, that can require other upgrades. So to keep cost down, truck were often not "Over spec'd" for their vocation. My guess is that 46K is the common spec where you are.

 In the US there are a lot of trucks that had 46K diffs, but not as many as those that had 40K.  Rockwell SSHD's were common in dumps, I don't know the Eaton Dana  share vs. Rockwell when it comes to dumps.

 Alot has to do with local laws, and allowed axle loads and length laws. Outside of "turnpike doubles" (2 45 or 48 ft trailers run on the turnpikes then broke into two separate units for off turnpike delivery) We didn't see a lot of high GCVW set ups. Heavy haul" was an exception.  I did some of my heaviest moves with 40K rears with a GCVW in the 160-170k range.  Those moves were well outside what the rears were "rated for" in GCVW, but  did the job just fine, They didn't exceed the 20K/axle in the weight they carried.

 It is why 34K and 40K centers are all the same, only the side gears and axle shafts are different. Same for 46K and 56K centers.  In full floating axles, the axle housing, bearings, brakes and axle shaft determine capacity more than ring gear size. Obviously, a 56K ring gear is going to be worked harder than a 34K even if they are powered by the same engine and transmission set, otherwise why pay for all the extra.

Edited August 29, 2023 by Geoff Weeks

[67RModel]

19 hours ago, Geoff Weeks said:

Air shift is my favorite, Yeah, push the button down, while under load, let up or step briefly on the clutch and it down shifts. Vacuum is my 2nd with electric being last on the list.

I have the Marmon with air shift and two K-7's with vacuum.  Marmon has a 3406, the K-7's are 269 gassers.

 Like anything else, a little time in, it becomes second nature.

 Eaton held the patent of the planetary gearing in the 2 spds, Timken, Detroit, Rocknwell also made 2spd's but they were a double reduction units that either hung off the front or on top like a Mack. The advantage of Eaton's design is the whole thing fit inside the ring gear, the disadvatage was you were limited in what planetary ratios would fit inside the ring gear, so most often they are around .73 between low and high.

 Eaton, Dana and Spicer rears are all the same company (Dana Holdings Corp) now, Spicer sold of the trans business to TTC, because Roadranger was part of Eaton, so they would almost be a monopoly if both Eaton/Roadranger and Spicer heavy transmissions were one and the same company.

 My air shift are electric over air. Air solenoid controls air pressure to the two shift cyl on the axles. You could use an air knob on the stick, but you still need an electrical signal to the speedo or speedo adapter to keep the speedo reading correctly in both ranges. Since I needed an electric signal anyway, I went with the typical "red knob" on the side of the trans stick. Also I had a 15 speed trans that needed its own shift knob. I could have made it all air, but it would have been a rats nest of air line coming up the stick.

 I agree, they should be used more, and if I ever had the chance to spec a truck the way I like, they would be top on the list. Doing more of the reduction at the rear, means you don't need as heavy a driveline, like you do when most the reduction is done at the trans. Like a two or three stick, you can't be in a hurry, but once you learn them, they are great.

Good information to know. Is there any type of safeguard to prevent one axle from shifting if the other solenoid or air shift cylinder fails to operate? I could only imagine the carnage of only one diff shifted and the other did not. Have you ever know that to happen? 

[Geoff Weeks]

Well, Eaton 3 speeds did just exactly that. The only problem would be if the PDL was also engaged while it happened.  Factory installs often have a interlock so the PDL can't be used if the axles are in high.

With one in low and one in high, the interaxle diff has to make up the difference. as I said the 3 speeds of the 60's did just that. still they held up well enough. I have also heard (from Glenn A) that some heavy haulers retro-fitted 2 spd rear rear and a single front to add splits when hauling heavy, and they did ok.

I never had a problem, and it would take major problem in the shifter for it to not shift. The air piston design is very simplistic and not much to go wrong. The earlier diaphragm air shift used a torsion spring like the electric shift do, and were more problematic, and the reason I don't like the electric and why Eaton dropped the diaphragm in favor of the piston unit.