Front to rear gear ratios...What is maximum variance allowed?

[RSchwarzli]

Put in an ARB Carrier.
Way more rigid then the sticker.

Well there is trouble! lol How are you?

Not sure what you're suggesting. How would a locker solve the gear difference of running a different gear front to rear?

 

[Ozymandias]

Hi, we are a little locked up in the southwest for now, wanted to go to Canada but with closed borders... no way. We'll see how that evolves.
I suggested to use tha ARB in the Dana 70 with your existing Gears, apparently the Carrier was the weak link so that would be my first step instead of swapping axles and gears.
The ARB as good as the TrueTrac Carriers are known to be way more capable then the OEM Carriers.

 

[SRay]

I have used a Tru-trac. Strong unit.

Robert: when your D70 got hot, what was the cause of the failure?

 

[NIsaacs]

I dont think I can. I sheared the carrier in half. lol Not sure that I can increase strength much more.

The D-80 is bigger/better in every way over the D-70. I know you know this so it makes sense to forego the 3.07. With the high 1st gear of the NV5600 I would think a heavy launch would be tough. My 3.55's struggle in 1st and need low range all the time. The difference between 3.55 and 3.31 is only about one tire size. I assume towing is more important than a daily driver or you wouldn't need the D-80. Just kick the 3.07 to the curb and don't look back

 

[SRay]

Robert: You’re not the first to shear a carrier in half.

I have as well but it wasn’t in my Dodge lol.

I went with a Detroit Tru-Trac. They don’t require special lube to be added, or servicing. They’re a lifetime unit.

If that is the only issue, then any of the after market, like Eaton, ARB, etc that has a great record in the off-road industry will likely be better built to handle your massaged Cummins.

There is a 1996 Dually 2wd in the states somewhere which had been in the Diesel Power magazine that swapped a D80 dual wheels to a D70 dual wheels to lighten the truck for drag racing. I forget what he used for the guts.

That truck has 1,300 hp and used M/T slicks to get 10’s in the quarter mile. 4wd trucks split the power with front end.

Also at the same time, it still pulls a trailer at the ranch, drives for groceries.

So if there is no gear option for the D80 to keep the 3.07, then try some of the aftermarket carriers.

 

[SRay]

NIsaacs: Robert here has 24 speeds in his W250, 3 shifters to use. He uses all of them

 

[NIsaacs]

NIsaacs: Robert here has 24 speeds in his W250, 3 shifters to use. He uses all of them

Then he for sure don't need 3.07's

I remember when he modified his t-case to use low range but I didn't remember if he had an overdrive unit. I would think that whatever his top gear is, 3.07's would require more power than 3.55's, so his lower rpms would really not help fuel mileage. Besides, with all his power, I don't think fuel mileage is a priority

 

[SRay]

NIsaacs: Robert also has the Gear Vendor Overdrive. I forget what his theoretical top speed is with the setup he has but I wouldn’t recommend he actually try it. Too many people with badges lurking around....

During the one Cummins Plant Tour trip back in 2013, his truck achieved 28 mpg. Best I got on that trip was 23 mpg while rolling on 35” Toyo M/T’s.

Robert is always up for a good challenge. Fuel mileage would be one of them.

 

[RSchwarzli]

Hi, we are a little locked up in the southwest for now, wanted to go to Canada but with closed borders... no way. We'll see how that evolves.
I suggested to use tha ARB in the Dana 70 with your existing Gears, apparently the Carrier was the weak link so that would be my first step instead of swapping axles and gears.
The ARB as good as the TrueTrac Carriers are known to be way more capable then the OEM Carriers.

Ahhhhh. I am following. Yes. That could be an option. My next concern is tooth strength and bearing load capacity as I have spun my bearings before too. lol All in all, i think that 70 is just a bit small for my loads.

I have used a Tru-trac. Strong unit.

Robert: when your D70 got hot, what was the cause of the failure?

The cause was shearing of the carrier bolts. That caused the clutch pack to expand.

The D-80 is bigger/better in every way over the D-70. I know you know this so it makes sense to forego the 3.07. With the high 1st gear of the NV5600 I would think a heavy launch would be tough. My 3.55's struggle in 1st and need low range all the time. The difference between 3.55 and 3.31 is only about one tire size. I assume towing is more important than a daily driver or you wouldn't need the D-80. Just kick the 3.07 to the curb and don't look back

You are 100% correct. Other than my towing, is all highway for min of 1000 miles at a time. So I like 3.07s for the highway. lol But, strength is more important than gearing. So trying to find the way to have both.

 

[RSchwarzli]

So if there is no gear option for the D80 to keep the 3.07, then try some of the aftermarket carriers.

That is true.

NIsaacs: Robert here has 24 speeds in his W250, 3 shifters to use. He uses all of them

Also true. lol

Besides, with all his power, I don't think fuel mileage is a priority

But I dont want to go backwards! My cruising speed is normally 80-85 depending on the state. I like still getting fuel economy, speed, reliability, and 5th over reliability.

Robert is always up for a good challenge. Fuel mileage would be one of them.

Yes. I see this as a rolling engineering experiment. Must not lose too much of anything by gaining strength. I dont like teeter totters. I like win win. lol So thats why I am trying to figure out what gears and tire ratios make this work.

 

[SRay]

Robert: your truck currently uses 285/75/17 tires? My memory is shot

 

[Ozymandias]

Is there a 3.07 Gear available for the AAM 12.5 Axle?
So maybe this could be a way to go?
Don't know, just brain storming.....

 

[SRay]

Ozymandias: interesting.....

 

[SRay]

I found this online while checking out AAM 12.5 that Ozymandias mentioned.

https://www.rushgears.com/?referrer...IxoDrmPKu6QIVlq_ICh3Fdw7lEAAYASAAEgL_7PD_BwE#

Maybe custom gears?

 

[RSchwarzli]

Robert: your truck currently uses 285/75/17 tires? My memory is shot

265/70/17 currently. In the OP my suggestion was to go to a 285 on a 3.31 so the front has a 3,07 and a 245..... that may even the numbers out.

Is there a 3.07 Gear available for the AAM 12.5 Axle?
So maybe this could be a way to go?
Don't know, just brain storming.....

Not that I can find. I would be happy to go that way too. But havent been able to find another axle with the 3.07 short of going down in stregth. AKA Dana 30.

 

[Ozymandias]

Yeah, I did some Research to, many are just 3.54 and a few 3.31. Non 3.07 so far I've seen. Maybe you want to go with a custom gear set that someone mentioned above.
I would definitely not mix tire sizes or ratios.
In any direction it would be bad, either for the view of the truck - or technically.

 

[RSchwarzli]

Ozy,

Yeah I wonder if thats playing with fire. Yet, was working on the farm tractor this weekend. 4wd unit..... front and rears are very different sized. Yes, I know not much speed involved. But it CAN do about 40 kph in 4wd...... hmmm.

 

[SRay]

I can easily imagine Robert’s daily having large tractor tires on the rear and small tractor tires on the front

 

[RWherley]

If your going to do something crazy, then go all the way, drop both axles to 3.55 and add a second gear vendor to your current one, then you wont have to worry about needing a rear drive shaft, itll just be all gear boxes, or i can set you up with a 3000 series Allison with with double over drive with 6th gear ratio of 0.65 and hang your gear vender behind that

 

[RSchwarzli]

Ooooh. .65.... Oh my! I like the sound of that! But I doubt that will bolt to my 205 and is that still a stick the 3000 series?