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Old 06-02-2014, 05:48 AM   #1
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Rear Gear Change ????

Just reviewing the specs( which i wish i had done better before purchase ). on my 2010 Dodge Ram 1500 Long Bed Reg. Cab 4.7 V8 3.55 gears, With the 3.55 gears it's listed at a 6,400# towing and with the 3.92 gears 7,400 #. Has anyone have any input on doing this ???? That extra 1,000 would but in our next TT and still keep that 20 % factor.

I also think it ain't as simple as it was in the old days, with all the computer stuff and electronics on board these days.

Jim
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Old 06-02-2014, 07:59 AM   #2
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I have two Ford diesel burner trucks. One has the 3.55 and the other a 4.10 rear end. The 3.55 drives fine on the freeway (with an overdrive) with no tow. The 4.10 revs too high above 55 mph for my taste. Notice I am talking just rpms on the freeway without towing. Towing ratings would favor the 4.10. Have you considered an overdrive or underdrive unit to give you more gear selection? When they give the tow ratings, is it because they think performance would be unsatisfactory, or does it have to do with some possibility that the drive train would break?
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Old 06-02-2014, 09:18 AM   #3
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When they give the tow ratings, is it because they think performance would be unsatisfactory, or does it have to do with some possibility that the drive train would break?
Performance, yes. But broken drivetrain only if caused by overheating while trying to pull too heavy a trailer. Drivetrain components such as springs, shocks, wheels, frame and tires broken because of overloaded suspension are not considered by tow ratings.

Manufacturers' tow ratings are GCWR minus the shipping weight of a new truck with no options other than make, model, body, engine, 4x2 or 4x4, and rear axle ratio. So all tow ratings are overstated because nobody tows a trailer with an empty tow vehicle that has no options.

To emphasize, tow ratings are based on GCWR. The GCWR is the combined gross weight a tow vehicle and trailer can have and still be able to climb a reasonable highway grade at a reasonable speed without overheating anything in the drivetrain.

One test Ford uses to verify GCWR is to drag a loaded trailer out of the lower Grand Canyon on highway 68 between Laughlin NV and Kingman AZ. If the tow vehicle cannot maintain at least the speed minimum (45 MPH?) for several miles up that steep grade without overheating anything in the drivetrain while towing at the tested combined weight, then they remove some weight and test again at the lower weight. The test vehicle has all sorts of additional instrumentation to monitor all relevant temps, including engine coolant, tranny fluid, and differential fluid. And if the engine is a turbo, they also include pre-turbo exhaust gas temperature (EGT). When the tow vehicle passes the test, then that is the max GCWR they will publish.

And I'll bet the other manufacturers have similar tests to verify their published GCWR.

One big problem with tow ratings is that GCWR is usually not the limiter of how much weight the tow vehicle can tow without being overloaded over the GVWR or rear axle weight rating. On my last two pickups, GCWR (and therefore tow rating) was much more than I could tow without exceeding the GVWR of the tow vehicle. 1999.5 F-250 diesel had GCWR of 20,000 pounds and a tow rating over 13,000 pounds, but I was overloaded over the GVWR when I was grossing about 16,000 pounds towing a trailer that grossed about 8,000 pounds. 2012 F-150 has GCWR of 14,000 pounds and tow rating of 8,400 pounds, but I'm overloaded over the GVWR when grossing 11,420 pounds with a trailer that grosses 4,870 pounds.

So take tow ratings with a grain of salt. Payload capacity is much more important than tow ratings when matching trailers to tow vehicles.
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Old 06-02-2014, 10:18 AM   #4
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All this is just a thought, checking with my local transmission shop also, but keep opinions coming.

Jim
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Old 06-02-2014, 10:46 AM   #5
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Originally Posted by rideandslide View Post
Just reviewing the specs( which i wish i had done better before purchase ). on my 2010 Dodge Ram 1500 Long Bed Reg. Cab 4.7 V8 3.55 gears, With the 3.55 gears it's listed at a 6,400# towing and with the 3.92 gears 7,400 #. Has anyone have any input on doing this. Jim
You didn't say if your truck is a 4X4. Gear change on a 2wd pick up is a simple job ( if you have the right tools ), and if your 1/2 ton still has the Chrysler 9 1/4 " differential under it that was in use when I retired in 07, probably 3 hours of shop time. The tone wheel and sensor, in the differential that signals the computers does not change , so no problem there. The 10% increase in RPM at all speeds, may drop your MPG, slightly, but won't bother the 4.7 OHC V-8.
Now 4X4 , and both differential changes $$$$. Front Diff is a bear.
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Old 06-02-2014, 02:20 PM   #6
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You didn't say if your truck is a 4X4. Gear change on a 2wd pick up is a simple job ( if you have the right tools ), and if your 1/2 ton still has the Chrysler 9 1/4 " differential under it that was in use when I retired in 07, probably 3 hours of shop time. The tone wheel and sensor, in the differential that signals the computers does not change , so no problem there. The 10% increase in RPM at all speeds, may drop your MPG, slightly, but won't bother the 4.7 OHC V-8.
Now 4X4 , and both differential changes $$$$. Front Diff is a bear.
Nope 4 X 2 rear wheel drive.
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Old 06-02-2014, 02:27 PM   #7
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2 wheel drive, just trying to look forward to our next TT at 6500# without spending another 20 grand, which at this point ain't going to happen
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Old 06-02-2014, 04:53 PM   #8
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For $20K, I would take the wear/tear on the 1500 and see how it does...if the only difference is the gearing, then you will just be working the truck harder on takeoffs and maybe in OD on the highway. My opinion...
Joe
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Old 06-02-2014, 05:55 PM   #9
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You are probably right. There might be other adjustments to computer software, speedometer, etc.

For a 4 X 2 a shop may only charge $500 to $700. Call a shop to check and ask if they do all the software and Speedo recalabrations.

Good luck
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Old 06-03-2014, 06:20 AM   #10
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For $20K, I would take the wear/tear on the 1500 and see how it does...if the only difference is the gearing, then you will just be working the truck harder on takeoffs and maybe in OD on the highway. My opinion...
Joe
I agree.
Most of the time the differential will possibly overheat the oil. Regular differential check might proved OK.
In the past GM differential did over heat but better oil has solved that.
In the industry I have improved the capacity of drives by flushing the oil for better synthetic.
Trials will be the only way to determine any problem.
Remember that loading the differential will be hard on the mileage. So watch and learn to drive conserving fuel and the result will be surprising.
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Old 06-03-2014, 06:51 AM   #11
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You have not mentioned if you have towed anything yet.
Why not take it out and see what your performance is?
If it does not suit your needs than you have to make a choice.
For $20.000 I would be curious what they are giving you.
If the vehicle is new why not trade for something more suitable?
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Old 06-03-2014, 08:29 AM   #12
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Yes, we have a 2000 Keystone Springdale Lite 25rkls at 4600# DW and have had it on several trips ( not in the hills yet ) and it has done fine, it's just that all the TT we look at (thinking of our next ) are in the 6500-7000# range.
Jim
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Old 06-03-2014, 08:50 AM   #13
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3.55 to 3.92 is not a huge jump. Take a look at your current tire size vs. a lower profile of adequate load rating. There are several tire size calculators on Goggle that will give the circumference of tires (tire rack has one that compares sizes). You might just find something between 3.55 and 3.92 that looks good to you as an overall ratio. Just takes a little arithmetic.
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Old 06-03-2014, 08:42 PM   #14
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Changing the axle ratio will not change the 'official' tow rating of your truck, but it will make your truck tow as good as other Dodge trucks that came factory equipped with the other axle ratio. But tow rating is really a subjective issue. Unless you do a lot of towing under severe conditions, constant hills, high temps or strong headwinds, then your existing axle ratio will still work, just slower on acceleration, maybe unable to maintain cruising speed without shifting to a lower gear (and higher rpms) and more driver fatigue. If the truck is your daily driver, you may not want to loose mpgs.

My truck is first intended for towing and rarely used otherwise, so for me the gear change would be a no brainer on a 2wd, maybe even a bigger change than just 3.92 ratio.
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