3.73 to 3.42 gear conversion results request

[MRFost]

I know at least one of these 3. 73 to 3. 42 axle conversions has been done out there. I'm not concerned with mileage change to the positive side.

I'm wondering what it cost to convert your 4x4; and if it got your RPM where you ultimately want it. I think I'd like to have the equivalent of a 7th gear. Bigger "tars" are on order. I hate not being able to run with the big dogs.

 

[BHolm]

I am curious as well. I am considering making a long term commitment to this truck and 2400 rpm @ 75mph doesn't work out so well running in the west.



I would do the work myself unless there is a major stumbling block somebody has run into. Parts cost?

 

[Motorhead]

Go to this site. The Diesel Garage - A Performance Diesel Site
On the front page there is a place on the left that says "Calculators". VERY handy! I figured out your gain, if you have stock tires.
With your G56 6th gear ratio being 0. 79, you should indicate about 63. 7mph in 6th @ 2,000rpm with 3. 73 gears. With 3. 42 gears you should be running 69. 7mph in 6th @ 2000rpm.
I think you could get the gearing results you want with taller tires at a lesser cost.
My '07, 5. 9 with the later 6th ratio (. 742), I can go with a 285-75-17 and get the gearing I want for empty driving and I bought an extra set of stocker wheels and tires for trailer towing where I need the lower gearing.

 

[RHestand]

I put H-2 wheels & tires on(315s) and after speedo. correction I now run 69mph at 2000rpms. I was hoping to get a little better mpg, but it didn't happen. (More mass?)I do like running at about 10% less rpms though,(less wear&tear)and also I think it's better geared for 2nd gear starts. Stock, about halfway through an intersection I had to shift into 3rd,now it's much better.

Also with the leveling kit and bigger tires it looks like it should look, IMO. Over all,I'm happy with this setup. Good Luck Ray

 

[Forrest Nearing]

while I would certainly assume that the 3. 42's would make for a great driving truck (LOVE the 3. 54's in the earlier trucks, couldn't imagine being forced to have 3. 73's) it seems that you could go with an aux OD and be ahead of the game moneywise

 

[DLane]

I think you could get the gearing results you want with taller tires at a lesser cost.

My '07, 5. 9 with the later 6th ratio (. 742), I can go with a 285-75-17 and get the gearing I want for empty driving and I bought an extra set of stocker wheels and tires for trailer towing where I need the lower gearing.

Complete lack of knowledge here.

YOU get the gearing with 285s AND . 74 OD. The older G56s w/. 79 OD need MORE than 285s to be drivable on the western Interstates. 3. 42s are a step in the right direction but still may not be enough. I have 285s behind my G56. 3. 73s in between, I can run thru a 35 mph zone w/out lugging my engine in

5TH. THATS JUST WRONG. I am thinking 3. 42s my still require a aux OD unit and 285 tires to keep proper RPMs on the highways. I just hate having to put on aux ODs

 

[MRFost]

Nobody answered the original question. I hear talk about what the RPM gets to; nobody answered what it costs to do the conversion. RHestand seems happy with putting on larger tires and a leveling kit. Motorhead doesn't have the same transmission; and assumes that I can't calculate. Others talk about an overdrive unit -- I wasn't asking about external solutions such as that. I think that the '07 & up overdrive ratio with the 3. 42's would be perfect for those of us that do not tow regularly, and do not tow heavy.

So, once again, I ask, has anybody done this conversion, and would you do it again to resolve the RPM issue? I have larger tires on order.

 

[BHolm]

Nobody answered the original question. I hear talk about what the RPM gets to; nobody answered what it costs to do the conversion. RHestand seems happy with putting on larger tires and a leveling kit. Motorhead doesn't have the same transmission; and assumes that I can't calculate. Others talk about an overdrive unit -- I wasn't asking about external solutions such as that. I think that the '07 & up overdrive ratio with the 3. 42's would be perfect for those of us that do not tow regularly, and do not tow heavy.

So, once again, I ask, has anybody done this conversion, and would you do it again to resolve the RPM issue? I have larger tires on order.

Yep, parts cost please!



I find it had to believe that adding the aux OD unit would be cheaper than swapping gears out. How much is a GV OD unit $2-3k?, plus you need to have the driveshaft shortened. Then what about 4x4 trucks? Can you install the OD between the trans and t-case to be able to use it in 4wd situations? Now you have front and rear driveshafts needing to be altered.



Gear sets can't be that expensive, even if, as I heard once, you need to buy a new front diff carrier. That could be the sticker though. Still looking to hear from a successful installer

 

[Rams-n-Hogs]

Yep, parts cost please!



I find it had to believe that adding the aux OD unit would be cheaper than swapping gears out. How much is a GV OD unit $2-3k?, plus you need to have the driveshaft shortened. Then what about 4x4 trucks? Can you install the OD between the trans and t-case to be able to use it in 4wd situations? Now you have front and rear driveshafts needing to be altered.



Gear sets can't be that expensive, even if, as I heard once, you need to buy a new front diff carrier. That could be the sticker though. Still looking to hear from a successful installer

Check this thread Better mileage!!! 3. 42 gears now available for 03+ AAM Axles!!! - Page 3 - Dodge Cummins Diesel Forum

 

[Motorhead]

Complete lack of knowledge here.
YOU get the gearing with 285s AND . 74 OD. The older G56s w/. 79 OD need MORE than 285s to be drivable on the western Interstates. 3. 42s are a step in the right direction but still may not be enough. I have 285s behind my G56. 3. 73s in between, I can run thru a 35 mph zone w/out lugging my engine in
5TH. THATS JUST WRONG. I am thinking 3. 42s my still require a aux OD unit and 285 tires to keep proper RPMs on the highways. I just hate having to put on aux ODs

Maybe you need to pull your head out of your rear!
I KNOW that the earlier G56 has the . 79 6th. That is why I bought a DEC. '06 5. 9. I just SUGGESTED that he could probably go to a taller tire and it would be cheaper than re-gearing. He could run 315's.

This isn't a site to SLAM others suggestions!

 

[BHaden]

Nobody answered the original question. I hear talk about what the RPM gets to; nobody answered what it costs to do the conversion. RHestand seems happy with putting on larger tires and a leveling kit. Motorhead doesn't have the same transmission; and assumes that I can't calculate. Others talk about an overdrive unit -- I wasn't asking about external solutions such as that. I think that the '07 & up overdrive ratio with the 3. 42's would be perfect for those of us that do not tow regularly, and do not tow heavy.

So, once again, I ask, has anybody done this conversion, and would you do it again to resolve the RPM issue? I have larger tires on order.

I second this comment. 6 months or so ago, several folks actually HAD the gears and were on the verge of installing them, then..... they just disappeared.

What happened to them? Did they ever get mileage numbers? Did they forget about this forum?

I have an 06 and get tired of crossing the AZ desert, usually loaded up but not towing anything, at 24-2500rpm at the speed limit (75) or a couple over. It's just not a happy thing. I also don't get the fixation with towing anything, anywhere in 6th gear. If you gear the axle low enough, you could tow the space shuttle over a mountain range, but then it would be REALLY unhappy when unloaded. They gave us 6 gears so we could pick a lower one when needed and then, seemingly, made that irrelevant by gearing the overall combo so low. I see no shame in downshifting up a hill when I have a big load behind me. If you haul large loads for a living, no problem; get the lower axle gears. That would make sense, but most of us are not in that category.

 

[betterthanstock]

My NV 5600 came with 4. 10 (duh, my mistake). I replaced tires with 315 after only 2000 miles. Then a year later, changed to the only thing available then, 3. 73, after a long talk with an AAM engineer. My cost, after selling the original gears, came to less than $1000.



I'm happy with 1920 rpm @ 70 mph, 2200 @ 80. I downshift on hills when towing heavy, which gives tremendous power, and saves the overdrive gear (the weak spot of the NV5600).



No more wishing for a 7th gear.



Your g56 has an even lower 1st gear than the NV, so you will be fine with the 3. 42. And 2nd gear starts will feel a lot better empty.

 

[JSanchez]

I, too, have been curious about the results from those who werer ready to do this conversion. There were quite a few that had the 3:42 gears on order-what ever happened to them? If you're out there, please post results.

 

[Regcabguy]

Gearvendor cost.

while I would certainly assume that the 3. 42's would make for a great driving truck (LOVE the 3. 54's in the earlier trucks, couldn't imagine being forced to have 3. 73's) it seems that you could go with an aux OD and be ahead of the game moneywise

Gearvendor does them here in San Diego. Quoted my friend $4,000 for our G-56's. Whew! Regearing or taller tires is sounding better. Motorhead's right on with the rpm's on mine. At 65mph w/285-70-17's I'm right at 2100 rpm.

 

[Regcabguy]

3.42 gears

I, too, have been curious about the results from those who werer ready to do this conversion. There were quite a few that had the 3:42 gears on order-what ever happened to them? If you're out there, please post results.

Hughes Racing Components posted that he could obtain and install them quite awhile ago. I spoke to Jason recently:no takers yet.

 

[KCraft]

2 years ago i talked to GV about their OD Aux's for my nv5600, they said its designed to drop the rpm's 500. so at that time i was turnin 1950 @70mph. so if all hold true then i should be looking at bout 1500rpm down the highway. that sounded great, upshifting would be required of course. do they make rearend conversion for 3. 54's????

 

[DLane]

Something to consider..... With a . 79 OD you would have to go to a 3. 08 to get what the 2nd gen guys get with 3. 55s and a auto(. 69OD) I do not see 3. 42s being anything but a step in the right direction.

 

[BHolm]

Something to consider..... With a . 79 OD you would have to go to a 3. 08 to get what the 2nd gen guys get with 3. 55s and a auto(. 69OD) I do not see 3. 42s being anything but a step in the right direction.

I think you are right on. That is probably why more haven't done the swap, a 200 rpm drop just isn't enough. I would rather see a 5-600 rpm drop in sixth. As mentioned, first in the G56 is already stupid low, almost useless, and there is nothing wrong with running fifth if sixth ends up too tall. That is unlikely though considering the power these trucks make.



I would spend a grand or so to see a bigger drop, the 20 mpg my 3. 73 auto trucks got would be nice the way fuel is priced today. If I could have 70 mph @ 1800 rpm life would be good.

 

[courierdog]

Assuming a manual G56 with the 3. 42 rear end 1900 RPM = 71 MPH
Assuming a manual G56 with the 3. 42 rear end 1800 RPM = 67 MPH
Assuming a 68RFE with the 3. 42 rear end 1600 RPM = 70 MPH
Using the Gear Calculator previously posted on TDR

 

[ronman]

I think you are right on. That is probably why more haven't done the swap, a 200 rpm drop just isn't enough. I would rather see a 5-600 rpm drop in sixth. As mentioned, first in the G56 is already stupid low, almost useless, and there is nothing wrong with running fifth if sixth ends up too tall. That is unlikely though considering the power these trucks make.



I would spend a grand or so to see a bigger drop, the 20 mpg my 3. 73 auto trucks got would be nice the way fuel is priced today. If I could have 70 mph @ 1800 rpm life would be good.

Just finished installing my GV OD last night, and I could not be happier. 70MPH is 1750 RPM in 6th with GV on. I was lucky and scored a new/never used GV OD for a really good price but in hinesight after driving the truck with it, I'd do it all over again even at full price!! It really transforms the truck into a highway cruiser, and will aid in towing my 28 ft tag too. I had a GV OD on my former '98 12V and loved it on that truck too. The difference on the 3 gen with early G56 is even more dramatic.