M1028 4.56 to 3.73 ?

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erasedhammer

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I was reading that the entire carrier needs to be swapped to the 4.10 and lower.
If that is so what do people recommend for new carrier to fit the 3.73 ring and pinion, I'm leaning between either Spicer or Yukon, unless theres a better price on another brand.
What do the costs end up being for both front and rear on average?
I hear the m1028 came with a locker in the rear and limited slip up front, how does this affect sourcing a new carrier?
This is for the Dana 60 and 70HD.

I also found a review on amazon for the motive gear D70-373 and someone said they couldn't fit the pair because it looked like it was made for a 4.56 carrier? Do they have 3.73 ring and pinions that are made for 4.56+ axles, or is that guy mistaken?

For reference, in conjunction with the gear change I will also be moving to 33" tires and nv4500. Since the nv has the granny gear and overdrive, I think the lower rear end ratio should give flexibility from around town, flat freeway cruising, and climbing mountain passes.
 

tobyS

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I was reading about the Dana 80 (I recently slavaged). It's 4.10 and below, anyway there is two different sizes in the 60, 70 and 80, all built the same, I believe. The 3.73 would take the 4.10 and under carrier.... If I understand the question. The 4.56 would be the "above 4.10", so no fit with 3.73. I'm not a HMMWV owner to know the sweet spot on the engine, tranny ratios or any advise. You are going from 37" to 33" ???....would seem to need the OD. It seemed Spicer was 40-50% higher price for the ring and pinon set than Yukon. Go through the math
 
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erasedhammer

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I was reading about the Dana 80 (I recently slavaged). It's 4.10 and below, anyway there is two different sizes in the 60, 70 and 80, all built the same, I believe. The 3.73 would take the 4.10 and under carrier.... If I understand the question. The 4.56 would be the "above 4.10", so no fit with 3.73. I'm not a HMMWV owner to know the sweet spot on the engine, tranny ratios or any advise. You are going from 37" to 33" ???....would seem to need the OD. It seemed Spicer was 40-50% higher price for the ring and pinon set than Yukon. Go through the math
This is on a stock m1028. Currently has 31" tires.
I don't want to totally crunch the 6.2s HP or potential mpg, so 37s are too much.
I was mainly asking what brand people seem to think is a better quality product for these trucks, Yukon and Spicer both seem very well built, just gauging the room.
 

98G

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This is on a stock m1028. Currently has 31" tires.
I don't want to totally crunch the 6.2s HP or potential mpg, so 37s are too much.
I was mainly asking what brand people seem to think is a better quality product for these trucks, Yukon and Spicer both seem very well built, just gauging the room.

37's and 4.56 or 33's and 3.73 will be just about the same final drive .

If 37s and 4.56 would crunch the HP and MPG so will 33's and 3.73s.
 

erasedhammer

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37's and 4.56 or 33's and 3.73 will be just about the same final drive .

If 37s and 4.56 would crunch the HP and MPG so will 33's and 3.73s.
33s weigh less, and 3.73 coupled with 0.73 overdrive drops the cruise rpm very low.
Not to mention 33s are easier to balance and cost less.

Not sure how the math works out, but wouldn't the extra weight of 37s bog the 6.2 more than 33s.
Considering m1008s have 3.08 gears I don't think 3.73 is going to completely ruin acceleration and hill climbing in overdrive (don't really expect to climb anything of significant grade in OD anyway)
 

tobyS

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Using pi times diameter the 31 will travel 97.4" , 33 will travel 103.7" and 37 will travel 116.2" per axle revolution. Lets use 2000 rpm and the .73 OD, the drivshaft will turn 2739 rpm. If you have the 3.73 the axle rpm will be 734 rpm and with 4.56 will be 600.7 rpm.

Thus the 3.73 at 2000 will go (31") 71,492", (33) 76,116" and (37) 85,144" and to compare with the 4.56 those numbers are (31) 58,508", (33) 64,455" and (37) 69,801". I'm leaving in inches to compare.

So the 4.56 using 37" tires (at 2000 engine) will go 69,801" and using 3.73 with 31 will go 71,492".

My point in the above post is that if you have the 4.56, you will also need to change the entire carrier to the one that is 4.10 and below to fit a 3.73...anyway yes, it can be done in your 70 series. Is it worth it to change not only ring and pinion, but the carriers of BOTH axles when the larger tires can bring you to a few % ?

I would also want to run those numbers using the granny gear (1st) of the early nv4500 versus the older.

Now going from 700 somethings in my A3 deuce to a 400 something....yea mon.
 
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98G

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Using pi times diameter the 31 will travel 97.4" , 33 will travel 103.7" and 37 will travel 116.2" per axle revolution. Lets use 2000 rpm and the .73 OD, the drivshaft will turn 2739 rpm. If you have the 3.73 the axle rpm will be 734 rpm and with 4.56 will be 600.7 rpm.

Thus the 3.73 at 2000 will go (31") 71,492", (33) 76,116" and (37) 85,144" and to compare with the 4.56 those numbers are (31) 58,508", (33) 64,455" and (37) 69,801". I'm leaving in inches to compare.

So the 4.56 using 37" tires (at 2000 engine) will go 69,801" and using 3.73 with 31 will go 71,492".

My point in the above post is that if you have the 4.56, you will also need to change the entire carrier to the one that is 4.10 and below to fit a 3.73...anyway yes, it can be done in your 70 series. Is it worth it to change not only ring and pinion, but the carriers of BOTH axles when the larger tires can bring you to a few % ?

I would also want to run those numbers using the granny gear (1st) of the early nv4500 versus the older.

Now going from 700 somethings in my A3 deuce to a 400 something....yea mon.
I like the numbers.

I come to the conclusion that EH likes 33's and is tweaking the other variables to optimize for them. (This is not a criticism).

Personally, I'd be reluctant to give up the 4.56s. Also, I'd rather spend the extra $ on 37" tires than spend the $ on a gear ratio swap. But then, I like 37s better than 33's all other things being equal.

The questions to ask yourself about gear ratios are -

1) is lowest low low enough?

2) is highest gear high enough?

3) what is cruising rpm?

I'll crunch the numbers for 4.56 and 33" tires. I suspect that just changing the transmission to the nv4500 with 33's provides very satisfactory results with the 4.56s.
 

Chaski

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I know you are not asking for input on this- but in my opinion going to 3.73 gears is going to make OD (5th) totally useless unless you live in a flat place.

I’d put in the NV4500 and tires first- then make gearing choices. My guess is that you will be happy with the 4.56 gears once you move to 33s and an OD transmission.
 

tobyS

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I know you are not asking for input on this- but in my opinion going to 3.73 gears is going to make OD (5th) totally useless unless you live in a flat place.

I’d put in the NV4500 and tires first- then make gearing choices. My guess is that you will be happy with the 4.56 gears once you move to 33s and an OD transmission.
You are right. Does going to 37 have any rub problems? Spend money for excellent tires.

Edit....had the 37"s stuck in my head....the 33 makes that OD usable, 65 at 2200 sounds great.
 
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erasedhammer

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I know you are not asking for input on this- but in my opinion going to 3.73 gears is going to make OD (5th) totally useless unless you live in a flat place.

I’d put in the NV4500 and tires first- then make gearing choices. My guess is that you will be happy with the 4.56 gears once you move to 33s and an OD transmission.
I know 3.73 plus that 0.73 is a pretty low rpm, but even if I didnt have the 3.73, would 4.56 and 0.73 be able to make it up a mountain pass?

My point is, that if in either gear ratio, overdrive cant be used when hill climbing, then both ratios would require shifting to 4th gear for any grade (1:1). So it would make more sense to get a more extreme OD rpm drop (with the 3.73) for going downhill and cruising on flat ground.
It would make a larger impact on mpg that way.

I definitely plan to do gear change last. First the nv4500, then tires. But I figured I might as well research this topic to death so I can plan out costs and parts for both routes.
 
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erasedhammer

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You are right. Does going to 37 have any rub problems? Spend money for excellent tires.

Edit....had the 37"s stuck in my head....the 33 makes that OD usable, 65 at 2200 sounds great.
When I had my humvee with the 4l80, it was pulling around 2100 at around 62mph. This rpm seems a bit high for these engines, they always seemed to pull better below 2000, so thats why I would aim for 1800 around 65. (I do plan on moving a 6.5 eventually)
 

erasedhammer

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Using pi times diameter the 31 will travel 97.4" , 33 will travel 103.7" and 37 will travel 116.2" per axle revolution. Lets use 2000 rpm and the .73 OD, the drivshaft will turn 2739 rpm. If you have the 3.73 the axle rpm will be 734 rpm and with 4.56 will be 600.7 rpm.

Thus the 3.73 at 2000 will go (31") 71,492", (33) 76,116" and (37) 85,144" and to compare with the 4.56 those numbers are (31) 58,508", (33) 64,455" and (37) 69,801". I'm leaving in inches to compare.

So the 4.56 using 37" tires (at 2000 engine) will go 69,801" and using 3.73 with 31 will go 71,492".

My point in the above post is that if you have the 4.56, you will also need to change the entire carrier to the one that is 4.10 and below to fit a 3.73...anyway yes, it can be done in your 70 series. Is it worth it to change not only ring and pinion, but the carriers of BOTH axles when the larger tires can bring you to a few % ?

I would also want to run those numbers using the granny gear (1st) of the early nv4500 versus the older.

Now going from 700 somethings in my A3 deuce to a 400 something....yea mon.
Makes sense, but my only reservation about 37s is the impact they can have on mpg. So a new math problem...

Theoretical MPG for: 4.56 + 0.73 OD + 37s
or
Theoretical MPG for: 3.73 + 0.73 OD + 33s

Assuming flat terrain freeway cruising.
I know mpg isnt something a 5/4 ton 80s truck is good at, but I'd at least like to get in the low 20s, maybe 25mpg.

I was originally thinking of going for 4.10s, but since I need to change the carrier to the 4.10 and down anyways, I figured might as well get a larger MPH gain for the amount of money I'd be spending.
 

cucvmule

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I have to ask but why not go and buy the truck you want to have?

Really by the time you swap out the drivetrain with money and time involved you would be time and headaches ahead.

Although 1 ton Chevrolets and GMC's are rare and hard to find they are out there. The very truck you want I have and with new majored 6.2 3.73 turbo 400 at 5500#'s and 285 BF all terrains the best mileage I have ever had was 18 and that was 70mph. Start getting into hills and standing on the pedal without letup and expect 8 to 10.

Maybe with overdrive you will gain mpg going downhill and flat roadways but anything else, hauling, hills, and that mileage quikly plummets. And hauling anything and you will be on the fuel all the time, 6.2.

And then my K30 500HP 454 dually with 35's 400 205, 4.10, 2800rpm at 70 I can get 7mpg, but I do not think that I can get better. The trade off of weight and rolling resistance bites into mpg no matter what the power you have. The original 454 was 10 at best with 235 85 tires.

The truck you have can be improved for sure. The overdrive trans and or an overdrive unit onto trans will help with mpg for a cost. And with the na 6.2 or 6.5 and into hills and you are not using the overdrive anyway.
 

tobyS

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I don't know enough about that engine to make those guesses... but it sounds very optimistic at 20. They have the aerodynamic shape of a brick and may or not have four wheels traveling in the same direction.
 

erasedhammer

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I don't know enough about that engine to make those guesses... but it sounds very optimistic at 20. They have the aerodynamic shape of a brick and may or not have four wheels traveling in the same direction.
I got 24mpg (average over a tank) with 6.2 and 4l80. Its possible, not at super speeds, but chuggin around at 50-55. These have better aero than a humvee.
 

erasedhammer

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I have to ask but why not go and buy the truck you want to have?

Really by the time you swap out the drivetrain with money and time involved you would be time and headaches ahead.

Although 1 ton Chevrolets and GMC's are rare and hard to find they are out there. The very truck you want I have and with new majored 6.2 3.73 turbo 400 at 5500#'s and 285 BF all terrains the best mileage I have ever had was 18 and that was 70mph. Start getting into hills and standing on the pedal without letup and expect 8 to 10.

Maybe with overdrive you will gain mpg going downhill and flat roadways but anything else, hauling, hills, and that mileage quikly plummets. And hauling anything and you will be on the fuel all the time, 6.2.

And then my K30 500HP 454 dually with 35's 400 205, 4.10, 2800rpm at 70 I can get 7mpg, but I do not think that I can get better. The trade off of weight and rolling resistance bites into mpg no matter what the power you have. The original 454 was 10 at best with 235 85 tires.

The truck you have can be improved for sure. The overdrive trans and or an overdrive unit onto trans will help with mpg for a cost. And with the na 6.2 or 6.5 and into hills and you are not using the overdrive anyway.
I dont know of any truck I could buy for a reasonable price that has a 6.2/6.5 diesel, nv4500 that wasnt built for towing or off roading.
I did originally look at civi trucks, but in my area, they were not very good prices and none were diesel.
The cucv was a good base platform to build exactly what I have imagined. Its already heavy duty, very little electronics, no interior, diesel.

I thought I've heard of nv4500 owners getting in the 20 mpg range.
I only got 18 mpg with my humvee 6.5 turbo and 4l80. So it doesnt seem like a crazy idea to hope for a little better mpg, after all the cucv has bettery aerodynamics than a humvee.
 

tobyS

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My numbers were right but I was way off on model....oops. Engage reading comprehension before commenting.
 

98G

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M1009 CUCV will get 20ish in stock form empty.

I doubt you're going to do much better than that no matter what you do to the M1008.

Taller tires = poor aero. The taller, the more pronounced.

Taller gears = better mpg, to a point. That point is the point that the engine no longer makes sufficient torque and you end up in the next gear down anyway. Like Toby, I'm not exactly sure where that point is with the 6.2.

MPG isnt really on the radar for me. Not enough to induce me to compromise any other aspect of performance.

If you go with 3.73's I'm interested to know what the final numbers/performance looks like.

Totally unrelated and not specifically relevant, but we have a jeep JKU with 3.73's and 35's. 5 speed automatic transmission, with 5th as overdrive. We spend a LOT of time in 4th gear empty. It downshifts at the slightest bit of grade. Tow a small trailer and any hill wants 3rd gear. I wish we had 4.56s or even 4.88s.
 

erasedhammer

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Just had a thought, I do want to eliminate the clutch based limited slips
M1009 CUCV will get 20ish in stock form empty.

I doubt you're going to do much better than that no matter what you do to the M1008.

Taller tires = poor aero. The taller, the more pronounced.

Taller gears = better mpg, to a point. That point is the point that the engine no longer makes sufficient torque and you end up in the next gear down anyway. Like Toby, I'm not exactly sure where that point is with the 6.2.

MPG isnt really on the radar for me. Not enough to induce me to compromise any other aspect of performance.

If you go with 3.73's I'm interested to know what the final numbers/performance looks like.

Totally unrelated and not specifically relevant, but we have a jeep JKU with 3.73's and 35's. 5 speed automatic transmission, with 5th as overdrive. We spend a LOT of time in 4th gear empty. It downshifts at the slightest bit of grade. Tow a small trailer and any hill wants 3rd gear. I wish we had 4.56s or even 4.88s.
So blazer with th400, 3.08 gears can cram 20mpg.
I dont see why I couldnt at least match that with the overdrive and closer gears in a m1008. Especially since a blazer with th400 doesnt have lockup, so theres some parasitic loss at cruise and acceleration.

I think I remember people commenting on the 6.2 being able to pull the truck down the road at sub-2000rpm range upwards of 65mph. Although probably not very efficiently. But still the engine seems to have plenty of torque to be efficient at, say, 55mph.
I plan to drive pretty lazily. After all, driving habits are the biggest factor in MPG.

As to your jeep example, I don't think a gasser is a great example of what mpg is possible in a truck like platform. A friend of mine has a ram 2500 cummins and manual and gets 25 mpg at 55mph. Of course it has all the torque it needs to push it down the road and up mountain passes in OD, but push it over 65mph and suddenly it can drop below 10mpg. And those trucks I believe have 3.73 with option for 4.10. To match their torque, they also weigh a lot more than a m1008, but pretty similar aero.
 
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