Gear ratio changes

[Gil Carbajal]

I have a question about rear differential gear ratios. I have a 2001 Dodge 2500 with a 24 valve Cummins engine and 47RE transmission. I tow a 12000 lb fifth wheel trailer. Our truck has 90000 miles on it mainly towing. I had the rear differential gears changed from 3:73 to 4:56 gear ratio for better grade climbing. Our truck is stock with stock size tires and it’s a 2 wheel drive model. I have been told that the low gear ratio is not good for the transmission or the engine, I do keep rpm’s below 2000 rpm when possible, sometime on heavy grades I need to down shift to lower gear and rpm’s go above 2500 rpm’s. The transmission is having some issues and the transmission shop recommended that I go back to the stock gear set. Any information would greatly appreciate. Thanks Gil

 

[Ozymandias]

The drive train is good for 3200rpm at the engine. No more no less.
And a 4.56 rear end makes it much easier for the transmission compared to the 3.73 you had before as the torque is built at the rear end.
And the higher your rpm the higher your line pressure in the transmission, the higher the holding forces at the clutches. The way you drive it is actually pretty bad for it, working it hard at low rpms.

Point is, this transmissions all had some flaws from the factory and need help to stand behind the Cummins, no matter what rear end you have. No big deal but it needs to be addressed right now that the transmission is going to be fixed.

I highly recommend you look for a different shop to fix your transmission. From my view they are not really knowledgeable about that certain vehicle configuration. I recommend a Goerend installer, they know their business.

 

[GAmes]

Are you sure of those gear ratios? Stock ratios was either 3.5 or 4.1. Either ratio would be sufficient to pull a 12,000 pound trailer although 4.1 might be a bit better if a lot of driving is done in the mountains. At 2000 rpm your speed would be about 50 mph with 4.56 gears so I really doubt that is what you have. All that being said, I agree with Ozy, you need to find a different transmission shop.

 

[SnoKing]

Are you sure of those gear ratios? Stock ratios was either 3.5 or 4.1. Either ratio would be sufficient to pull a 12,000 pound trailer although 4.1 might be a bit better if a lot of driving is done in the mountains. At 2000 rpm your speed would be about 50 mph with 4.56 gears so I really doubt that is what you have. All that being said, I agree with Ozy, you need to find a different transmission shop.

I had a 2001.5 for 14 years with the lower 4:10 gears. It towed 12K fine after getting the DTT transmission treatment, Stage 1 injectors, Comp in EZ mode and a PDR35-12W turbo! Nothing before 2003 came with 3:73's.

My 1993 W250 came with terrible brakes, terrible non locking torque converter and 3:56 or3:54 gears.

 

[Gearclash]

The 5.9 is not an N14. Let it turn! Ag tractors with the 5.9 Cummins or its derivative are usually set to high idle at 2400 RPM and pull rated hp at 2200 RPM and do that all day long year in year out. With an auto trans I could see running a 4.10 rear but not with the manual. I have a ’99 with a manual, couldn’t for love or money get me to go from the 3.54 dif to a 4.10.

I have pulled long hard and heavy with this truck and the only think I would change would be closer gears and a higher overdrive in the trans.

 

[SnoKing]

The 5.9 is not an N14. Let it turn! Ag tractors with the 5.9 Cummins or its derivative are usually set to high idle at 2400 RPM and pull rated hp at 2200 RPM and do that all day long year in year out. With an auto trans I could see running a 4.10 rear but not with the manual. I have a ’99 with a manual, couldn’t for love or money get me to go from the 3.54 dif to a 4.10.

I have pulled long hard and heavy with this truck and the only think I would change would be closer gears and a higher overdrive in the trans.

Yes the manuals have less of an overdrive radio vs the 47RE.

 

[Gil Carbajal]

The drive train is good for 3200rpm at the engine. No more no less.
And a 4.56 rear end makes it much easier for the transmission compared to the 3.73 you had before as the torque is built at the rear end.
And the higher your rpm the higher your line pressure in the transmission, the higher the holding forces at the clutches. The way you drive it is actually pretty bad for it, working it hard at low rpms.

Point is, this transmissions all had some flaws from the factory and need help to stand behind the Cummins, no matter what rear end you have. No big deal but it needs to be addressed right now that the transmission is going to be fixed.

I highly recommend you look for a different shop to fix your transmission. From my view they are not really knowledgeable about that certain vehicle configuration. I recommend a Goerend installer, they know their business.

Thank you for your input. I was able to locate a Goerend installer in my area and I am having them to take care of transmission issues, rebuild and upgrades.

 

[Ozymandias]

Fantastic, that are good news. Please keep us updated how that turns out and what was actually wrong with your transmission.

And if you want to keep it, now would be the perfect time to also put one of Goerends Coverters into it. It is so much more fun to drive when the torque of that engine is finally put on to the ground instead of heating up the transfluid.
Converter is THE best mod for driveability ever for our trucks.

 

[Gil Carbajal]

Fantastic, that are good news. Please keep us updated how that turns out and what was actually wrong with your transmission.

And if you want to keep it, now would be the perfect time to also put one of Goerends Coverters into it. It is so much more fun to drive when the torque of that engine is finally put on to the ground instead of heating up the transfluid.
Converter is THE best mod for driveability ever for our trucks.

What experience do you have with Suncoast components? They said they install Goerend and Suncoast components.

 

[Ozymandias]

The components are pretty good so far, quality stuff. But for the Converter itself I'd always choose Goerend over Suncoast.
The point is that they know what they do with mix & match and I think that is given with a Goerend installer.

 

[SnoKing]

Fantastic, that are good news. Please keep us updated how that turns out and what was actually wrong with your transmission.

And if you want to keep it, now would be the perfect time to also put one of Goerends Coverters into it. It is so much more fun to drive when the torque of that engine is finally put on to the ground instead of heating up the transfluid.
Converter is THE best mod for driveability ever for our trucks.

I would note the my DTT 89% TC was a big drivability improvement, however tight TCer are not good for off roading, which I found out going down Shafers Hill in Moab. They make low range quite jumpy also.

 

[Road Dog]

A higher differential gear means less stress on the transmission. The stock truck had either 3.54 or 4.11 gears. I have 3.54 gears and with a camper am at my GVW. I generally climb hills at 2,200-2,500 RPM to get my boost up and my exhaust temps down.

I'd like 4.11 gears but upgrading two axles gets pricey.

 

[AH64ID]

Lower gearing only means less transmission stress if the wheel torque is the same. If the engine output is the same the stress is the same, but with the lower gearing there is more torque to the wheels.

So average stress for the trans is down, but peak torque remains the same.

 

[BigPapa]

Something else here that I've not seen mentioned. At higher RPM due to the lower gearing, the engine AND transmission are, how shall I say it, being used more?

To explain what I mean (Now, I'm just using numbers here, not the actual numbers because I don't know what they are), but if your turning 1700rpm at 60mph with 3.54's and 1900rpm at 60mph with 4.11's, your engine and transmission are turning another 200 times per mile with the 4.11. If you made a 2500 mile trip, that means your crankshaft turns an extra 500,000 times, your injectors fire an extra 500,000 times.

 

[AH64ID]

Something else here that I've not seen mentioned. At higher RPM due to the lower gearing, the engine AND transmission are, how shall I say it, being used more?

To explain what I mean (Now, I'm just using numbers here, not the actual numbers because I don't know what they are), but if your turning 1700rpm at 60mph with 3.54's and 1900rpm at 60mph with 4.11's, your engine and transmission are turning another 200 times per mile with the 4.11. If you made a 2500 mile trip, that means your crankshaft turns an extra 500,000 times, your injectors fire an extra 500,000 times.

But you also have less impact stress on the crank and rods, so it’s a trade off.

 

[Cummins12V98]

Someone is blowing smoke up your skirt!!!

 

[petersonj]

that means your crankshaft turns an extra 500,000 times, your injectors fire an extra 500,000 times.

Must be using 2-stroke oil.

Actually, the injectors would fire 250,000 times..., just nit picking

- John

 

[Turbo Terry]

Then there’s fuel economy to think about also. I don’t think 12 k is really a very hard pull unless it’s always in the mountains

 

[GilCarbajal]

What experience do you have with Suncoast components? They said they install Goerend and Suncoast components.

Hi, we had our transmission rebuilt by Inglewood transmission in Fullerton CA. They found that the converter clutch was burnt, the front pump was damaged, second gear band was burnt and several other components. They replaced all the components with upgraded Goerend billet input shaft Goerend clutches and bands and a Goerend converter. Picked up the truck and the shift quality is nice, I am looking forward to our next RV trip. Thanks again for your input Gil

 

[GilCarbajal]

Hi, we had our transmission rebuilt by Inglewood transmission in Fullerton CA. They found that the converter clutch was burnt, the front pump was damaged, second gear band was burnt and several other components. They replaced all the components with upgraded Goerend billet input shaft Goerend clutches and bands and a Goerend converter. Picked up the truck and the shift quality is nice, I am looking forward to our next RV trip. Thanks again for your input Gil

Does anyone have any experience with Banks exhaust brakes? I have run one my truck since the truck was new, I was wondering if exhaust brakes can damage automatic transmissions due to the lock up mode when slowing down/ braking.