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Old 06-25-2007, 10:09 AM   #1
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Hi guys (and gals),

Been lurking here for a while and decided to get some advice from you folks. I have an '04 Dodge Ram 4x4 with the 4.7 liter engine. Maximum torque output is around 300 lb.ft. The differential gears are 3.55:1. I am considering a gear change, but since this vehicle is four wheel drive, the expense is quite high - around $1300+ for the change. If this were a two wheel drive vehicle, I would probably just go ahead and do the swap. However, 1300 bucks is a lot of dough to spend for an experiment. I should mention that the Dodge, when in Tow/Haul mode, locks out 5th gear, but is still allowed to hit 4th (the first overdrive gear).

I tow an X189-FBR Shadow Cruiser Fun Finder that has a GVWR of 4200#. Fully loaded and wet, we are tipping the scales at ~3400#. We just took an 1800 mile round trip from California through Arizona and New Mexico. On flat land, we did very well, cruising at 60-65 MPH. However, the transmission shifts constantly from 4th to 3rd and back again. When we hit any substantial rise in the road (especially with any head wind), the truck shifts down to second. In second gear, we are winding up around 4000 RPM @ 60 MPH. This doesn't bother me terribly, as long as it doesn't happen often. However, it was happening more than I would like.

Now for the questions. I would like to know from those of you with experience, how a gear change to either 4.10's or 4.56's will affect my towing, especially at highway speeds. I ran some calculations and came up with the following:

Assuming a constant torque of 300 lb.ft. (I know torque is not constant, but I had to use some baseline for calculation), I would gain about 22% torque by going to 4.56 gears (instead of my current 3.55). That sounds great, but I'm worried about whether I would have enough torque available to keep the transmission from shifting into second gear under normal driving conditions. Does this calculation sound correct? Will the transmission run cooler? (I do have a trans temp gauge with the sender in the line going to the trans coolers). Will the transmission shift back and forth less?

I know that some of this may be a bit subjective, but I'm hoping for a voice of exerience to chime in here. Sorry for the long post.

RP
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Old 06-25-2007, 10:09 AM   #2
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Hi guys (and gals),

Been lurking here for a while and decided to get some advice from you folks. I have an '04 Dodge Ram 4x4 with the 4.7 liter engine. Maximum torque output is around 300 lb.ft. The differential gears are 3.55:1. I am considering a gear change, but since this vehicle is four wheel drive, the expense is quite high - around $1300+ for the change. If this were a two wheel drive vehicle, I would probably just go ahead and do the swap. However, 1300 bucks is a lot of dough to spend for an experiment. I should mention that the Dodge, when in Tow/Haul mode, locks out 5th gear, but is still allowed to hit 4th (the first overdrive gear).

I tow an X189-FBR Shadow Cruiser Fun Finder that has a GVWR of 4200#. Fully loaded and wet, we are tipping the scales at ~3400#. We just took an 1800 mile round trip from California through Arizona and New Mexico. On flat land, we did very well, cruising at 60-65 MPH. However, the transmission shifts constantly from 4th to 3rd and back again. When we hit any substantial rise in the road (especially with any head wind), the truck shifts down to second. In second gear, we are winding up around 4000 RPM @ 60 MPH. This doesn't bother me terribly, as long as it doesn't happen often. However, it was happening more than I would like.

Now for the questions. I would like to know from those of you with experience, how a gear change to either 4.10's or 4.56's will affect my towing, especially at highway speeds. I ran some calculations and came up with the following:

Assuming a constant torque of 300 lb.ft. (I know torque is not constant, but I had to use some baseline for calculation), I would gain about 22% torque by going to 4.56 gears (instead of my current 3.55). That sounds great, but I'm worried about whether I would have enough torque available to keep the transmission from shifting into second gear under normal driving conditions. Does this calculation sound correct? Will the transmission run cooler? (I do have a trans temp gauge with the sender in the line going to the trans coolers). Will the transmission shift back and forth less?

I know that some of this may be a bit subjective, but I'm hoping for a voice of exerience to chime in here. Sorry for the long post.

RP
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Old 06-25-2007, 10:39 AM   #3
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Actually it sounds as if your 355's arnt to far off form where you need to be. 410's would be the best of your two options that you show, however I would consider 373's as this would give you the best of both worlds. The 456 set would be great for towing... at 3500 rpms just to maintain hwy speed... as I dont think your truck is a 100% tow vehicle the 456's would not be a smart choice. 373 is a fairly common gear set, as such you may be able to pick up a used and not abused set for considerably less $$$ from the shop that was going to do your install. a lot of heavy off roaders will go the 410/456 route when adding over sized tires. The installer may have access to these used but not abused sets.
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Old 06-25-2007, 10:58 AM   #4
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It might be more cost effective to sell the truck and buy another one already set up like you want. A late model 4x4 such as yours shouldn't be too difficult to sell.

Another option is to investigate the feasibility of an auxiliary transmission such as offered by US Gear.
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Old 06-25-2007, 05:12 PM   #5
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I looked into a similar gear change on a Chevy 1500 a couple of years ago. You are right, about $1300 for the change until I found out that the gear ratio I had selected was not an option from GM in that model, and thus the computer couldn't be reprogrammed for the gears I had chosen. Seems the transmission shift points, etc are all controlled by engine speed, and the higher reving gears screwed up the computer. Moral: Make sure the gear ratio you select is available as an option from Dodge, so the truck computer can be reprogrammed for the gear change.
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Old 06-27-2007, 04:38 AM   #6
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Have you ever considered smaller tires? That may be all you need. You could easily have a towing set and an everyday driver set. You can change gears ratios also by changing outside tire diameters. One or two sizes down might get you where you want to be. What tires are you running right now?

I had a link to a chart that would tell you what tire size to choose to get a final gear ratio change. If I can find it I'll pass it on.
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Old 06-27-2007, 04:43 AM   #7
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Here it is:

www.4lo.com

The calculators are on the left side of the webpage.
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Old 06-27-2007, 05:03 PM   #8
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ACCU auto parts is a great research site. Use the calculator button at top right of the page to find each gear "after" ratio, compared to stock. For some reason Dodge salesmen never know that Dodge recommends the 3:73 ratio for towing. I suspect this is because the 3:55 ratio gets better fuel mileage, and they have more sales leverage.
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Old 06-28-2007, 06:02 AM   #9
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After researching this a bit, I have decided to go to the lower gears. I'm probably going to go 4.56. This decision is based on a couple of things.

I sat down a few days ago and put together an Excel spreadsheet that calculates RPM based upon speed, tire size, transmission ratios and final drive ratio. The transmission in my truck is a 545RFE and has the following ratios:

1st = 3.0
2nd = 1.67 (upshift)
2nd = 1.5 (downshift)
3rd = 1.0
4th = .75 (1st overdrive gear)
5th = .67 (2nd overdrive gear)

The transmission can be locked out of 5th by the tow/haul switch on the steering column. However, 4th gear cannot be locked out on an 04 model.

So, with 3.55 gears in 4th gear @ 60 MPH, the engine is turning over 1732 RPM, which gives me next to nothing in torque. With 4.56 gears at that same speed, I will be turning 2224 RPM. Much closer to where I need to be. All of this with 31" tires (stock size). With the 4.56 gears, I will still only be turning 2318 RPM at 70 MPH in 5th gear. Maybe a little higher than I would like, but not bad.

This truck usually does not see freeway speeds except when we are towing. Most of my driving is back and forth to work, 5 miles each way, on surface streets. Fuel consumption is not a big factor for my everyday driving, although I doubt that I will see much of a difference.

With a change from 3.55 to 4.56, I will gain a 22% torque advantage - which is really hard to pass up. Plus, it puts the engine in a better RPM range for making torque.

Anyhow, that's my reasoning.

Ron
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Old 06-28-2007, 07:37 AM   #10
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I 100% agree with going to 4.56 gearing ! small motors need RPM to make power , having said that forget 5th gear for towing . be happy with 3rd and 4th gear and the added RPM many not cause a loss in fuel economy. Lugging a motor in the end will cause it to run hot and have detenation problems with poor fuel , this det will cause the computer to retart the spark causing poor fuel economy also. Back a few years ago I had a 70 chevy with a 4.88 gears and 1:1 high gear with 27" tires . Yes it was busy under the hood at 65 mph but it could blow the tires off the rims in 3rd gear just by hitting , it never did that with the stock 3.73 gears it had OEM.
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Old 06-28-2007, 07:55 AM   #11
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Sorry Mark, I think I may have been mis-leading with my last post. I didn't mean to imply that I would tow in 5th gear. 5th would be reserved for running empty. I was just trying to point out that when I am empty and running in 5th, I would still be at a reasonable RPM. Sorry about my confusing post about that.

And I appreciate your input. I've seen a few posts on other boards where folks have done the same thing I am going to do and they seem to love it. I'll get back to everyone after I get it done and have a chance to tow with it.

Ron

PS - I'm thinking you're right about the fuel mileage being better while towing with better gears. That engine won't have to work as hard, regardless of the added RPM.
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Old 07-06-2007, 05:05 PM   #12
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Well, I took the plunge today. I went to a 4 wheel drive specialty shop and put a deposit down on the 4.56 gears. The gears are on order now and should show up in 4 or 5 days. Then I'll have to take it in to have them installed. The price is $1368 out the door - not exactly cheap, but better than the other two prices that I rounded up.

There happened to be another customer in the shop getting some exhaust work done while I was there. I go to chatting with him about the gear swap. He did the same thing to his Ford F-150 with a 4.6 liter. His stock gearing was 3:54 (I think that's what he said). He said the difference was night and day. He couldn't say enough good things about them. Anyhow, they will be installed in plenty of time for our next camping outing, so I'll report back what I have found after that trip.

Oh, and I also reset the MPG computer. So, I'll see what the mileage is before and after the change with my normal daily commute back and forth to work. I know the MPG computer probably isn't all that accurate, but at least it will be an apples to apples comparison.

Ron
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Old 07-06-2007, 06:00 PM   #13
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You might want to break in the new gears before towing. In the case of my Dodge, the owner's manual recommended 500 miles of unloaded driving prior to towing.

Unless you reset the PCM for the new gears, the speedometer and odometer will read substantially high. This, of course, will throw the MPG calculation into a cocked hat.

Rusty
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Old 07-06-2007, 08:20 PM   #14
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Rusty,

On the 3rd generation Ram, the sensor for the speedometer reads a pickup on the ring gear, so the speedo will be correct. It only changes with tire diameter. I should have at the very least 500 miles or so before the next time I tow. We are going out at the end of August, so if we take the truck for all of our errands and such, we should have at least that. Thanks for the tip.

Ron
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