Considereing Swapping to 3.73 rear, but ...

ilarson007 · Aug 6, 2014

Considereing Swapping to 3.73 rear, but ... (jk, they don't have 3.73s for the 1500)

... Can't seem to find the information I am looking for. I'm just trying to figure out what differential I need, what I have, and how difficult it would be to swap it. I went on RockAuto to check out what was there, and I see this (04 Ram 1500, quad cab, short bed, 4.7L, NV3500, 3.55 rear end, 2WD):

So I'm kinda lost there to begin with. Different numbers of splines, 8.25 vs 9.25," LSD vs. open diff.

Additionally, I haven't even began to look into recalibrating the speedometer so that it is correct after swapping these. If anyone has any help there...

Graygoose · Aug 6, 2014

Order them from Matt, he will get you what you need.

Gears

ilarson007 · Aug 6, 2014

Graygoose said:
Order them from Matt, he will get you what you need.

Gears

Doesn't list 3.73s on there.

Graygoose · Aug 6, 2014

If they are available, Im sure he can get them.

RamRod37 · Aug 6, 2014

Here this will give you a build sheet of what all your truck came with from factory goto page and to left Equipment listings and enter your vin # it will give you the full breakdown of what your truck has Including rear diff ratio
Dodge - Contact Us

Id say yours probably has a 3.92 mine is a 4.7 2wd 05 model and its 3.92 the build sheet will tell you

ilarson007 · Aug 6, 2014

RamRod37 said:
Here this will give you a build sheet of what all your truck came with from factory goto page and to left Equipment listings and enter your vin # it will give you the full breakdown of what your truck has Including rear diff ratio
Dodge - Contact Us

Id say yours probably has a 3.92 mine is a 4.7 2wd 05 model and its 3.92 the build sheet will tell you

Thanks, I'll look after work. The ad for the truck said that it had 3.55 gears in it. If I have 3.92 gears, I'm in real trouble for towing.

ilarson007 · Aug 6, 2014

RamRod37 said:
Here this will give you a build sheet of what all your truck came with from factory goto page and to left Equipment listings and enter your vin # it will give you the full breakdown of what your truck has Including rear diff ratio
Dodge - Contact Us

Id say yours probably has a 3.92 mine is a 4.7 2wd 05 model and its 3.92 the build sheet will tell you

Actually, had the VIN on my insurance card. Yep, truck came with 3.55 gears.

RamRod37 · Aug 6, 2014

ilarson007 said:
Thanks, I'll look after work. The ad for the truck said that it had 3.55 gears in it. If I have 3.92 gears, I'm in real trouble for towing.

3.92 would have been better for towing its a lower gear the higher gear ratio # the lower the gear is

Graygoose · Aug 6, 2014

Yea, not worth the cost to go from 3.55 to 3.73's...

RamRod37 · Aug 6, 2014

Graygoose said:
Yea, not worth the cost to go from 3.55 to 3.73's...

yeah if I was going to swap gears Id at least go to a 3.92 some even go to 4.56 but most are 4x4 trucks doing the 4.56

myoung84 · Aug 6, 2014

Towing with a 4.7L you're going to want at least 4.10s. Also, I don't believe 3.73s exist for the 9.25" rear axle, that's a gear option for the HD trucks. If they did, it's only a 94 RPM difference at 70 MPH. The 4.7L up to 2007 only has 235 HP stock. It needs a lot more gear to get it moving and maintain highway speeds, even more so when towing. I had an 04 Quad Cab with 3.92s and stock size 33" tires and hated it the first time I hitched up my new boat. I ended up re-gearing to 4.56s and it helped a lot, but still not great with the auto transmission. It soon got traded on a Hemi Ram. That NV3500 manual trans will help some...

With the NV3500, 4.10s would be a good choice since you only have one overdrive gear. Depending on the weight you're towing and the frequency, 4.56s might be better. Here's the ratios of that trans if you're interested.

FIRST 4.02
SECOND 2.32
THIRD 1.40
FOURTH 1.00
FIFTH 0.73
REVERSE 3.55

You have the 9.25" corporate rear axle. Could have LSD (limited slip/anti spin), it was an option. Need to pull the build sheet to confirm. The 8.25" axle is the front axle in a 4x4. You also don't need a whole new axle, just the gears and install kit, then find a good installer that has experience with Dodge axles. Install can run anywhere from $250-500 depending on the area.

Assuming you have stock 20" wheels with 275/60/20 (33") tires, here's your RPMs at 70 MPH in 5th gear.

3.55: 1847
3.92: 2040
4.10: 2133
4.56: 2373

If you have stock 17" wheels with 265/70/17 (31.6") tires, here's your RPMs at 70 MPH in 5th gear.

3.55: 1929
3.92: 2027
4.10: 2228
4.56: 2478

Lastly, speedo recalibration is not required with a gear swap. The tone ring is bolted to the ring gear so a gear change doesn't have an effect.

TylerB · Aug 6, 2014

myoung84 said:
Towing with a 4.7L you're going to want at least 4.10s. Also, I don't believe 3.73s exist for the 9.25" rear axle, that's a gear option for the HD trucks. If they did, it's only a 94 RPM difference at 70 MPH. The 4.7L up to 2007 only has 235 HP stock. It needs a lot more gear to get it moving and maintain highway speeds, even more so when towing. I had an 04 Quad Cab with 3.92s and stock size 33" tires and hated it the first time I hitched up my new boat. I ended up re-gearing to 4.56s and it helped a lot, but still not great with the auto transmission. It soon got traded on a Hemi Ram. That NV3500 manual trans will help some...

With the NV3500, 4.10s would be a good choice since you only have one overdrive gear. Depending on the weight you're towing and the frequency, 4.56s might be better. Here's the ratios of that trans if you're interested.

FIRST 4.02
SECOND 2.32
THIRD 1.40
FOURTH 1.00
FIFTH 0.73
REVERSE 3.55

You have the 9.25" corporate rear axle. Could have LSD (limited slip/anti spin), it was an option. Need to pull the build sheet to confirm. The 8.25" axle is the front axle in a 4x4. You also don't need a whole new axle, just the gears and install kit, then find a good installer that has experience with Dodge axles. Install can run anywhere from $250-500 depending on the area.

Assuming you have stock 20" wheels with 275/60/20 (33") tires, here's your RPMs at 70 MPH in 5th gear.

3.55: 1847
3.92: 2040
4.10: 2133
4.56: 2373

If you have stock 17" wheels with 265/70/17 (31.6") tires, here's your RPMs at 70 MPH in 5th gear.

3.55: 1929
3.92: 2027
4.10: 2228
4.56: 2478

Lastly, speedo recalibration is not required with a gear swap. The tone ring is bolted to the ring gear so a gear change doesn't have an effect.

Yep, no 3.73s for the 9.25" axle.

ilarson007 · Aug 7, 2014

RamRod37 said:
yeah if I was going to swap gears Id at least go to a 3.92 some even go to 4.56 but most are 4x4 trucks doing the 4.56

My truck is 2WD.

myoung84 said:
Towing with a 4.7L you're going to want at least 4.10s. Also, I don't believe 3.73s exist for the 9.25" rear axle, that's a gear option for the HD trucks. If they did, it's only a 94 RPM difference at 70 MPH. The 4.7L up to 2007 only has 235 HP stock. It needs a lot more gear to get it moving and maintain highway speeds, even more so when towing. I had an 04 Quad Cab with 3.92s and stock size 33" tires and hated it the first time I hitched up my new boat. I ended up re-gearing to 4.56s and it helped a lot, but still not great with the auto transmission. It soon got traded on a Hemi Ram. That NV3500 manual trans will help some...

With the NV3500, 4.10s would be a good choice since you only have one overdrive gear. Depending on the weight you're towing and the frequency, 4.56s might be better. Here's the ratios of that trans if you're interested.

The biggest thing I am struggling towing is my team racecar. The Uhaul trailer is just over 2100 lbs, and the car is close to 3000, so that's just north of 5000 lbs. In comparison, I can't even tell when I'm towing the 8x8' snowmobile trailer with the quad on it.

myoung84 said:
You have the 9.25" corporate rear axle. Could have LSD (limited slip/anti spin), it was an option. Need to pull the build sheet to confirm. The 8.25" axle is the front axle in a 4x4. You also don't need a whole new axle, just the gears and install kit, then find a good installer that has experience with Dodge axles. Install can run anywhere from $250-500 depending on the area.

It says "Corporate 9.25 LD Rear Axle" on the sheet; I'm assuming that is light duty. Also, I was hoping to just be able to purchase a diff and swap it in. Or an entire used axle; I do all my own work, is this install really that hard? And more than likely, I'll be able to get the Eaton differential shown in that screenshot for very low cost, maybe even at cost.

RamRod37 said:
If you have stock 17" wheels with 265/70/17 (31.6") tires, here's your RPMs at 70 MPH in 5th gear.

3.55: 1929
3.92: 2027
4.10: 2228
4.56: 2478

I know these trucks will never be economical, but it seems like I'd be turning way too many RPM's for regular driving with 4.10s or 4.56s. To clarify, the majority of the time I drive it, it will definitely be to work and back (39 miles, one way). So I can't just entirely shoot my 14mpg in the foot. Lol. I mean, I do have the bike, but I can only ride until about November? Or whenever I decide it's finally too cold. Or it snows.

myoung84 said:
Lastly, speedo recalibration is not required with a gear swap. The tone ring is bolted to the ring gear so a gear change doesn't have an effect.

Not visualizing what you're saying, but that's good to know.

JPT · Aug 7, 2014

Gear work is an art. Swapping axles are easy if you can find the ratio you want. But setting up gears are not just an easy DIY job.

ilarson007 · Aug 7, 2014

Hey everyone, here is an idea (I am new to trucks, so I don't know much about them). A guy I work with suggested I spend that money to buy a programmer instead of a new gear ratio in the rear... He said I can free up quite a few extra HP and improve fuel economy by a few mpg. I'm used to Subarus, so I don't know anything about tuning a truck motor, but he mentioned that the factory tune for trucks is usually a P.O.S. aimed at passing emissions. Thoughts? Looks like a used axle and a programmer are right about the same cost.

myoung84 · Aug 7, 2014

Higher RPM doesn't necessarily mean lower economy. It's all about the load on the engine. If the engine is lugging to maintain speed you'll be sucking more fuel than an engine running a little faster but working less.

I think your best bet is to find a used axle with 3.92s and factory limited slip. That would be an easy swap. As mentioned, doing a gear swap is an art and requires experience and special tools.

A tuner is a good idea, but won't replace a mechanical gear advantage. Also, don't expect 3 MPG increase. You might get 1-2 at most...

ilarson007 · Aug 7, 2014

myoung84 said:
Higher RPM doesn't necessarily mean lower economy. It's all about the load on the engine. If the engine is lugging to maintain speed you'll be sucking more fuel than an engine running a little faster but working less.

I think your best bet is to find a used axle with 3.92s and factory limited slip. That would be an easy swap. As mentioned, doing a gear swap is an art and requires experience and special tools.

A tuner is a good idea, but won't replace a mechanical gear advantage. Also, don't expect 3 MPG increase. You might get 1-2 at most...

Let me rephrase, fuel economy increase when not towing, and more power to tow with. I've seen at least one programmer that you can load a custom tune with... This is going to be leagues ahead of any OTS tune.

I think though, I will first do the programmer, just because install is easier, and then I will also do the 3.92 rear end. They cost roughly the same money, but my time is so limited right now. Plus I'm not going to be towing anything probably this winter, so the additional fuel economy (if any) from a programmer will help me more than the different rear end will in the short term.

JPT · Aug 7, 2014

ilarson007 said:
Let me rephrase, fuel economy increase when not towing, and more power to tow with. I've seen at least one programmer that you can load a custom tune with... This is going to be leagues ahead of any OTS tune.

I think though, I will first do the programmer, just because install is easier, and then I will also do the 3.92 rear end. They cost roughly the same money, but my time is so limited right now. Plus I'm not going to be towing anything probably this winter, so the additional fuel economy (if any) from a programmer will help me more than the different rear end will in the short term.

You would be surprised what gears does to everyday driving. It is like a new vehicle. My jeep wrangler was 3.73 and I went to 4.56. It was like driving a race car LOL.

ilarson007 · Aug 7, 2014

JPT said:
You would be surprised what gears does to everyday driving. It is like a new vehicle. My jeep wrangler was 3.73 and I went to 4.56. It was like driving a race car LOL.

Right, well I definitely don't wanna go to 4.56 lol. I would agree with the comment above, the 3.92 with LSD is probably what I'm gonna do. I just think I'm going to do the programmer first, because I can start saving a bit on gas with that, counteract the drop in mpg from the gears, and also improve power to compliment the gears. I think the 3.92s are a good comprimise, as I'm not towing "all the time." I'll retain some economy, and still have a little extra grunt behind it. My dad has an 06 with the Getrag 6 speed, and the 3.92 rear, and it's not a major difference, but I can tell that he's got a little more grunt going on (same 4.7L)

JPT · Aug 7, 2014

ilarson007 said:
Right, well I definitely don't wanna go to 4.56 lol. I would agree with the comment above, the 3.92 with LSD is probably what I'm gonna do. I just think I'm going to do the programmer first, because I can start saving a bit on gas with that, counteract the drop in mpg from the gears, and also improve power to compliment the gears. I think the 3.92s are a good comprimise, as I'm not towing "all the time." I'll retain some economy, and still have a little extra grunt behind it. My dad has an 06 with the Getrag 6 speed, and the 3.92 rear, and it's not a major difference, but I can tell that he's got a little more grunt going on (same 4.7L)

I would greatly benefit from lower gear ratios. I end up having to rev to high and drive around in 4th on the highway to have some power. I think lower gear ration (higher numerically) would actually improve my gas mileage.

It did on my jeep, but I had 35" tires.

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