Overdrive or Taller Gears for Fuel Savings

[Bernie]

There a little pricy so fuel economy payback is years.

Any hard numbers of MPG before and after? Again, I do a lot of miles so I might one of the few the math works out for. If the math works out the other advantages are icing on the cake.

 

[kscheffler]

I have documented 1. 5 to 2. 0 mgp increase with the GV on 1500 mile trips so they do pay back. Plus the noise reduction is worth as much as the increase in fuel economy. They also are a lot of fun to work with; you can always find the perfect gear/rpm/torque combination; unlimited possibilities...

 

[Bernie]

So, my payback will be ...

-If I drive about 45k miles a year

-Diesel averages out at about $3 per gallon

-Currently getting 16 MPG (about $8440 of fuel per year)

-Get 18 MPG with an OD (about $7500 of fuel per year)

-Save $940 per year

-Total cost of OD with install about $3700

-Four years to pay back OD



If I wait about two years for my Cummins warranty to be over (100K miles ), that means I will need to drive the truck for 6 years to have it work out to my advantage (which is 270k miles).



So, If I keep the truck to 300K miles, I will save about $630 in fuel total (at $3 per gallon).



I would like to save, but that is a long time for payback on the investment. Now, if fuel prices go up (which they will), it will be better. I also have the advantage of having more gears for towing, and lower RPMs (wear) on the motor, and less noise in the cab.



I'll have to think about it and see what I come up with. I want to talk to a couple of axle shops and see what they can to to change the gearing in my diffs.

 

[Bernie]

Anydoby have one in my neighborhood

This may be asking a lot, but does anybody have an OD unit on their thrird gen with a 6 speed manual with in a few hours drive of Jamestown, Olean, Buffalo, or Rochester, NY.



If someone would be in to it, I'd love a chance to take a ride (as a passanager or driver) and see one in action.



Thanks

 

[klenger]

I've heard that some of the aux transmissions do not have a long life span. It might wear out before it can pay for itself. I feel like my truck already has too many gearboxes. I'd never add another one. One option might be to get some taller, but narrow profile tires. Just getting bigger (wider and taller) tires probably does not help fuel economy all that much because of the increased rolling resistance and unsprung weight.

 

[DPKetchum]

I have NO first hand knowledge of this but I have read in the past from 1st generation through 3rd generation trucks that 2 mpg increase is wishful thinking. More like . 5 to 1. 0 etc. You lose some H. P. and torque going through the gear vendor or U. S. gear unit etc.

 

[WOT]

give me some 3. 42 gears and i would deal with using 5th more when towing and just add some more power to make up for it

 

[Lektrikman]

US Gear overdrive

Guys, I have an 05 with the G56, 4WD and I share the same concerns you do about the poor mileage and the engine wound up like an eight day clock at highway speeds. I once had a Gearvendors unit behind a Ford C-6 trans and I used it as the fourth speed in the transmission. Even though the Gearvendors always worked well, every time I changed lube oil in the GV unit it came out black, leading me to be concerned about clutch wear. Given the fact that the Gearvendors unit has a cone clutch as well as a small piston type oil pump driven by the output shaft, I was always concerned about reliability and I swore my next OD transmission would be a US Gear unit.

Now to my point. There have been a number of posts on this website about the US Gear OD unit and the fact that US Gear has told people that they were not going apply their unit to any new transmissions. I have been corresponding with people at US Gear about designing an adapter to mount their unit BEHIND the Tcase rather than where they normally mount it, which is between the main transmission and the Tcase. My point in mounting the US Gear unit behind the Tcase is I don't need to drive 75 mph in 4WD, but I do need another gear for slightly better economy as well as reduced engine rpm at highway speeds. I am willing to shorten my rear driveshaft to install an OD unit, but I am not willing to rework the entire driveline by having to relocate the Tcase, shorten one drive shaft and lengthen another, plus modify my fuel tank to accomodate the normal mounting position of the US Gear unit. So to me it makes a lot of sense to mount the US Gear OD unit behind the Tcase, plus I think there very well might be more owners willing to make minor modifications to their truck to install the OD unit.

So... ... . with all that said, after the normal customer service guys at US Gear got tired of telling me NO, I was referred to the US Gear vice president. So I wrote him a decent email stating my reasons why I thought they needed to make an adapter for mounting their unit behind the Tcase, as well as the wider market segment a rear mounted unit might appeal to. So far, I haven't received any emails flatly refusing to entertain my suggestion, so I'm hoping they are considering my ideas. If any of you guys are serious about a US Gear overdrive unit I'd suggest you write the vice president of US Gear and make your desires known. His name is Don and his email address is: -- email address removed -- Maybe if enough of us write and show an interest, they will reconsider their position and design the adapter. Let me know what you think... ... ... ... ... ... Lektrikman

 

[Regcabguy]

New gearing.

Sounds like the answer to everybody's problems is for AAM or aftermarket to manufacture higher axle ratios to switchout. If enough people ask for it maybe it'll happen.

 

[J.BURCHFIELD]

I put a gear vendor on my 98 12v. with 3:55 rear. I turn 1,500 RPM at 70 MPH. Before it was 2,000 RPM. Makes a big difference in the noise level but no difference in fuel milage. I put in marine injectors a while back (after the gear vendor) and got 3 mpg better towing but no difference not towing. Never will figure that out. -- email address removed --

 

[Bernie]

Next Question

Thanks for all the great input.



So, IF I decide to get one, there appears to be a few choices:



This one from Gear Vendors

http://www.gearvendors.com/dmanual.html



Drivetrain.com

http://www.drivetrain.com/new_overdrive/Dodgemanual/overdrivedodgmanual.html

(which looks suspiciously like the Gear Vendors one with some electronics available to run it)



And the one from US Gear

http://www.usgear.cc/dual_range.htm

It looks like you have to modify the heck out of your truck to make this one fit!



Any thoughts which one would be better than another? Are there any others out there?

 

[cojhl2]

Now at the time we tested, he had 315's and I had my current set-up which is 305's on 20" rims. I know that makes the ratio a little more favorable

Remember the speedometer and Tach don't recognize tire size other than original. (unless recalibrated)

 

[Bernie]

If the spedo connects at the diff (which I'm to new to Dodge to know where the pick up is), I'm pretty sure it would read an overdrive correctly.



If it picks it up at the back of trans, then I will need to re-calibrate it.



Also, I don't see the tach being affected at all. That should be motor speed only, and has no connection to wheel speed.

 

[cojhl2]

I went back and reread my post and see that it was not written very clearly.



Someone earlier was describing a comparison between two Dodges and their Tach/Speedmeter ratios 2000RPM@65MPH as an example. Then they went on to say something about the difference in tire sizes on the two vehicles.



What I am saying is tire size has nothing to do with the Tach/Speedometer ratio. Tire size does have to do with that ratio and actual land speed however.



I did not mean to get into where the Speedometer was taken off the system I assumed it was subsequent to the overdrive.



Sorry for the confusion, hope this clears up what I was saying. .

 

[wsurf]

Bernie,

I don't think it has been mentioned in this thread and I forgot to mention it. The Gearvendor cannot be used in 4X4, where the US gear can.



The GV unit goes behind the transfer case and whereas the US Gear goes between the trans and transfer case. You only need to cut the rear drive shaft with the GV unit and you need to cut both with the US Gear unit.



This may not matter to you, it didn't to me, but thought that it needs mentioning.

 

[Bernie]

Bernie,

The Gearvendor cannot be used in 4X4, where the US gear can.

Thanks. I noticed that as well.

Now, the Gearvendor and Drivetrain.com unit look very similar. If I had to take a guess I would say that Drivetrain.com sells the same unit, and then adds their electronics.



If I understand correctly the Drivetrain.com units are at the back of the trans, but still OK for 4x4. The electronics disconnect the OD if you are going in to 4x4. I know this would be very simple on the electronic (switch) 4x4 system, but I have a lever on the floor. I'll need to find out more about it.



I have no problem not having an OD when I'm in 4 wheel drive. I don't need to go 75 or worry about fuel economy when I'm using the front axel.



I would have to remember not to engage 4x4 while the OD was engaged.

 

[steved]

The electronics disconnect the OD if you are going in to 4x4. I know this would be very simple on the electronic (switch) 4x4 system, but I have a lever on the floor. I'll need to find out more about it.

You still have a switch on the manual lever tcases... the one that lights the 4wd light in the dash...



steved

 

[wsurf]

The GV unit would automatically disengage if you put it in 4X4.

 

[Bernie]

You still have a switch on the manual lever tcases... the one that lights the 4wd light in the dash...

steved

Good point! I forgot about that.

 

[ENafziger]

I was seriously thinking about purchasing one of these units as well... until I realized their limitations. US Gear allows the use of exhaust brakes, but requires a 2-second wait before engaging... it seems like you would loose a lot of momentum waiting 2 seconds for a shift. The Gear Vendor unit is not compatible with exhaust brakes. If a company develops a product that can be shifted quickly and allow the use of the exhaust brake, I'd be interested...