Changing differentials vs. aux overdrive

[DPKetchum]

I still vote for some 19. 5s. As soon as I can afford it thats the way I'm going.

 

[Blkdawdg]

RWheeler ::



If you want to swap I have 3. 73's in my '03 with 15K on them and I live in texas. PM me if interested.

 

[XJSuperman]

The 19. 5's will NOT reduce your cruising RPM's at all... the tire diameter will be what changes it IF nothing else (transmission and/or diff gears) is changed too.



265/70/19. 5's run 34. 3--34. 5" tall. . which is right in line with the 315/70/17 BFG's a lot of us are running... . so the 19. 5's will only reduce cruising RPM's IF the tire diameter is also increased to MORE than what he;s already running.

 

[1rumrunner]

Originally posted by Mopar_Mudder

I think that the overdrive is really a waste for gaining milage also.



Think about it, you are going to spend close to $3000 to put it on. With that if you gain an average of 2mpg it will take 250,000-300,000 miles to pay for its self. And face it, most of people don't keep a vehicle that long, and will and overdrive even take that many miles?



If you can't swap for cheap with some one that has 3. 73's I would forget it and just drive. The RPM's aren't going to hurt the Cummins, this same basic motor used in marine aplications may run for days at a time full rpm.

What?!! You haven't bought something just because it's fun!!???

 

[Mopar_Mudder]

Originally posted by 1rumrunner

What?!! You haven't bought something just because it's fun!!???

Oh heck ya, I have wasted much and often, LOL. Just didn't want to see someone waste money to try and save money.

 

[djbobo]

How's this for fun....

I'd get a US gear 20% underdrive, that installs between the transmission & x-fer case, to use with ex. brake, 2 wheel low & 4 wheeln' fun. Then also install the GV 22% overdrive, that installs after the x-fer case, for the fun of shifting under hard acceleration & haveing the double overdrive for highway use.







dj



ps I think that if you do get the GV unit it is possible to use it in any car or truck with the cost of $400 in adapters. since the unit itself is the same one used in all of their applications. So my math says it will pay for itself in about 34,300 miles assuming you keep it for your next truck.

 

[Spooled-up]

I've heard some things that you should look into with the GV unit. I don't have one, so not sure it's true or not, and hopefully someone will correct me if I'm wrong.



I remember someone posting that they saw little or no improvement in mileage with the unit. Apparently it makes so much heat with the reduction that it requires frequent lube changes.



I also remember someone posting that just slowing down will give you much better mileage. I have as much problem with this as the next guy, but it's probably true. You won't catch me experimenting with this one.

 

[Blakers]

Originally posted by Spooled-up

I also remember someone posting that just slowing down will give you much better mileage. I have as much problem with this as the next guy, but it's probably true. You won't catch me experimenting with this one.

Yea, I've also heard that it will improve mileage if you always go down hill.



Seriously, I think the secret to good mileage (or kilometerage in Canada) is keeping it between 1800 and 2000 rpm.

 

[GColeman]

Originally posted by RWheeler

Just got my 04 2500 4x4 CTD. LOVE IT. Only thing is I had to settle for a 4. 10 diff with the six speed transmission... About 85% hwy miles >70 MPH at 200 miles a trip. I put the 315 tires on it and I'm turning 2350 RPM's at 70. Thinking about how to get the RPM's down at hi speeds. Should I go with an aux overdrive or try to change the diff to 3. 73 or lower?

Check your PM. Maybe we can work a deal.

 

[jcarey]

Here a review of the GV, not bad reading...



http://www.rvdoctor.com/product.html

 

[RWheeler]

just ran back from the coast last night loaded up with the boat. The first time to brake in with a load. She's now at 1200 miles and running. Calibrated the speedo with my GPS, when running at 60 on the speedo I'm actually running 66. 4 mph. With stock 265's i was running 2300 rpm @ 70 mph. With 315's now running about 2000 rpm @ calibrated 70 mph. still trying to get as close to 1800 rpm as possible. The computer quoted 12. 1 mpg while loaded up, but that's without figuring in the tire compensation.

 

[Dkevdog]

Here is a thread that has a good bunch of info about the Aux trans and mileage and gear ratios in general.



Old US Gear Thread



Kev

 

[Sherman]

thanks guys for the info,considering the GV but didn't know about the no jake use, saved $3195. plus install

 

[wsurf]

I know this is an old thread and shouldn't chime in, but my 2 cents on the GV unit. You can't make it pay milage wise. Greatest benefit is for those that have DRW and the 48RE like me: splits gears for towing and running empty it is noise reduction thru lower RPM's. There is a slight mileage benefit. Since I'm limited on tire sizes (DRW) an over/under drive seemed to be the other choice. By the way, the GV unit is superb and it's just another toy to put on my machine!