JuiceLee

My 2004 4x4 (NVG5600) has 4.10s and can pull more than I need. I've got stock H2 wheels and tires. I have a 24 foot V-nose tandem axle trailer that, last time I moved, weighed a total of 10k lbs. I mostly run unloaded and on the highway. I can't remember exactly what it is, but something like 2100RPM at 65MPH. I have a very light foot. I get about 17-19 in the city (well, rural Oklahoma...I should say "town") and more like 17-18 on the highway. If I'm cruising on the back roads at 55mph or so it goes up to 22-23 MPG. The correlation I see, of course, is that my RPM on the highway is what's killing my gas mileage.

I'm reading lots of great stuff about getting lower revs for cruising. I do not want big tires for looks...in fact, I didn't really want to put the 315s on the hummer wheels. I'd like to minimize the "unsprung" weight. I shy away from the idea of swapping out the front/rear end for sacrificing my ability to tow...the times that I do have to. When I do tow it tends to be pretty significant distance...like coastal VA to Oklahoma (twice)...or Florida to Anchorage AK (upcoming). I'm intrigued by the idea of an overdrive. Total costs of solving this problem involved, I have to say that the very least I'll get away with is about $1500.

So how does this GV overdrive work? Is it a switch you hit that turns it on when you need it? Is it always on and responds to power required? If I've got a manual, how do I get into 6th over? Speaking of which...what the heck is x-over...a gear I shift into or a button I push? How is my 4x4 ability affected? Can my wife, who can't use a can opener and barely handle my truck, drive unaffected...without trashing the $3000 upgrade?

And I apologize in advance for my complete ignorance on the issue, but it seems like it's kinda hard to find a guide to overdrives for "the rest of us"...even on this forum site. Please don't feel like you're getting too basic when describing how this thing works. If they only had this in a children's novel format. It seems like the fight of giant tires vs tranny changes vs rear end swaps vs (name it) is well fought on this site...I'm trying to get edumacated on the basics of overdrives.

snoyes

I love how you called you transmission an NVG5600 instead of the NV 5600. Hmmmm... Having pulled that road to Alaska a few times with the trailers, the #1 thing I was glad to have was the Jacobs Exhaust brake. Nothing like cresting the 9% downgrade for the next 3 miles with a 10K lbs trailer behind you... So much more comfortable and controllable with the Exhaust Brake.... Once you get into Canada's Yukon, you won't be travelling more than 35 MPH anyway. Frost heaves can launch your truck and trailer (think Dukes of Hazzard).

For the GV unit, most guys have had good luck with them. Most report the fuel savings to be about 2 MPG, which may take some time to recover the $3000 sticker price and if you don't install it yourself, another $500 install... (i'll let you run the cost benefit analysis on this one, I forsee lots of miles for the break-even point). Hence the reason most go with the larger tires, as it costs less and drops the RPMs much like the GV unit will.

As for operation, you'll have a guy with one of these chime in and let you know how he operates it. Probably not too cosmic, I wouldn't worry about your wife tearing the GV unit up....

Prior to making the travel to the North country chime in on here. Alot of guys have done this multiple times... Some great advice here...

JuiceLee

NVGs...you get the idea. "220, 221, whatever it takes"

Yeah, not as much worried about the fuel savings as I am throwing my motor a bone for the everyday driving that I do. I'll take the opportunity to keep my mouth shut regarding the benefits vs downsides to throwing huge tires on, that battle rages on in at least 5 or 6 threads. Decreasing rotation by 20% or so would require some sort of tractor tire...and defeat the use of a 4.10 rear end when I need it. I'd love a cake, and to eat it too where possible.
As for the engine brake...not a bad idea! Did you cross in Seattle? How's the drive around September? I am hoping (hint hint) that someone with a GV unit will tell me exactly how this thing works.

snoyes

Hopefully someone with a GV unit will chime in. I don't imagine you will need to worry about the larger tire affecting your ability to pull your trailer. Now if you are consistently hitting the 25,999 GVW then I would say the 4.10s help.

Honestly, decreasing by 20% is a little agressive. A good goal is 10% which can be gotten using 35s, which you should have on there with the 315 BFGs (equal about a 34.6 inch tire).

I would love to have a GV unit for use myself, but they do not make it for the G-56s (my year of 6 speed manual).

Most of my travels to and from ALaska I didn't drive all the way to Seattle, I actually entered Canada via Montana then worked my way over. Probably about 40-50 miles of unpaved roads the last time I did it (all due to construction). I Did the trip in early October once, which is right about the point it switches to winter. I did not have issues, but one of my buddies that was a few days behind me got hit by a bad ice storm. He had to stay put for about 2-3 days till things cleared. Just FYI, many of the fuel stops are seasonal, which almost got me on the ALCAN during the October trip. Quite a few places were closed.

Anyway how's the weather out there?

Bigiron

I don't have a Gear Vendors OD, but I do have a US Gear 20% OD on a Cummins powered Suburban. Technically, it is not really an overdrive but a gear splitter as it operates in all gears including reverse when it is engaged. I believe the GV works pretty much the same way. One of the big advantages that an OD has over larger tires, is that it doesn't increase rolling friction, or raise the height of the vehicle which will increase air drag. Both of these effects decrease fuel mileage.

redeyedracer

The GV i had on my ford (which is the same as the dodges) is operated by a red push/pull button on the stick and you shift it just like a gear, although mine was a little slow so i would always click the switch then puch in the chutch, count to "two one-thousand" and then engage the clutch....ALSO the GV units will not work at slower speeds (less than 35mph or so) due to the torque multiplication from the tranny. This can get pretty hard on the drivetrain if you forget to turn off the GV while downshifting as the GV will automatically shift out of OD with a loud BANG!!! BUT I ran the GV on that ford for over 200Kmi routely pulling 20 to 35klbs without any problems. Ohh yeh one more thing, you probably wont see more than a 1mpg with the GV.
THE BOTTOM LINE - Its a very cool toy but even the G56 trucks will not save enough fuel to justify the cost....BUT the cool factor does!!!!

JuiceLee

thanks red eye, the way you describe it makes it sound more or less like a "hi/low" for each gear I already have, where the "hi" is overdriven and the "low" is stock...which would make the concept much simpler than I had expected if true. So you could drive around without ever engaging the aux tranny unit (stock)?

What's the engagement sequence? I'm in 5th w/o OD engaged. I pull the OD lever, clutch in, wait a second, shift into 6th, release the lever and clutch and turn the radio up? Or, is that when I can explain to my wife what a great purchase it was? In any case, I guess with the delay of getting to my stock gears vs overdriven gears...I imagine there being a problem as I climb a hill and find the need to downshift...waiting the requisite 3 seconds or so while coasting to a rapid stop to shift out of OD. OR, if I was downshifting from OD 6th to (stock) 6th...can I disengage OD while loaded? Just backing off the gas? Just pushing the clutch in without shifting out?

It's not as much for MPG as it is for long term engine wear...even though it kills me that I get better mileage in town than with cruise on below the speed limit on the interstate.

redeyedracer

Yes, it is a hi/lo for each gear, exactly how you describe in your first paragraph.

Yes you can and most of the time will drive around with the GV disengaged (low or stock), although you could split every gear above 35mph if you wanted.

Shift sequence - most of the time you drive around with the GV disengauged until you get into 6th, then engage the GV as if it where 7th gear!!!wwhhhooo!!!

Durability - Keep in mind this is only MY experience with a GV behind a severly abused 7.3/6spd ford - Although the GV has a second or two delay during shifting they claim it is designed to be shifted UNDER LOAD!!!! and it is....but in the manual tranny trucks it slams hard!!! I have down shifted under the conditions you described above without the chutch or backing off the throttle...i did not expect that unit to last...hopefully the ones for the dodges hold up as well....I even let my employees drive it, so I'm sure the wife cant hurt it.

Jim O

I have a Gear Vendors on a 03 4x4 with a NV5600 but mine has 3:73s. I also have a Jacobs ex brake. At 120 kms. or 75MPH I am turning about 1650 to 1700 ( close as you can read it). On mine the overdrive won't work below about 25mph on yours with 4:10s I would expect it to start working about 17mph. It will give you about 11 speeds ahead and about ten would be usable.
The OD ratio is .78 to 1 and I think it is Ideal the ratio in 6th in the NV5600 is .73 to one so there is only about 200 rpm between 5th over and 6th then there is 6th over. It give you a drop of about 500rpm (with 3:73s). You have to wire it for a 4x4 so that the GV will not go into OD when in 4WD and if you have a Ex brake it should be wired so the ex brake will not work when in OD. I installed mine myself and it is not a big job change the Ujoints to grease type when you shorten the rear drive shaft the technical people at Gearvendors are a big help with the wireing and any problems you may have. My unit has been in for over 100,000 miles 160,000 Kilometers and the only thing I don't like is the short oil change periods. Because I have an Ex brake and it uses the switch on the gear shift I went with a Hurst Tee handle with a switch in it (supplied from Gear vendors). I have not had one problem with the GV. and I would I would buy another one in a minute. When I bought this one a US dollar was worth $1.40 Canadian and I still think it was worth it . As mentioned by another poster the money pay out is a long way down the road but this makes driving the truck a pleasure. Also when you are towing you can go down or up 1/2 a gear. Besides the Cummins is a lugger not a buzzer.
Before I bought this I drove a friends brand x truck with a US gear OD unit and I also drove another friends with a GV and there was not comparing the GV unit was easier to shift. One poster said it took a second or two to shift, mine is only that way when it is cold. Below 0 F ( I use synthetic oil in the GV) If you go on the GV site I think it is www.gearvendors.com they will send you a brochure. the tech line is 800-999-9555
Sorry for the long post but I really like the GV.
JMOP
Jim O

JuiceLee

Thanks guys. No need to apologize for the long post...I learned a lot there. I didn't know that there was a restriction on exhaust brakes and an OD working at the same time. Why is that?
I know they have 4x4 transfer case units...your saying that your unit is basically a 2WD unit that is electrically disabled in 4WD? It makes sense, I don't need OD in 4WD, mostly for unloaded 2WD highway driving anyway.
Talking about lugging: What's the "no lower than" RPM that you guys use towing?

redeyedracer

I think the exg brake lockout is due to the fact that the power is going backwards through the GV on the "coast" side of the gears....i think with some exg brakes it is possible to put out alot of reverse hp which the gv is not designed for...Yes i remember the short oil change intervals, but its pretty easy to do, i just used a good synthetic and chaged it every other oil change.

Lugging is defined as a point where the engine will not accelerate with the current load...could be 1500 or 2200....generally most people agree that the CTD's are most efficent in the 1700-1800rpm range...i use the exg temps and boost levels to dictate the most efficent opperating rpms for a given load.

Jim O

There is a spring applied brake to give you some hold back on the hills but it is not designed for the extra hold back of the ex brake. The ex brake works best in the lower gears anyhow. Most of the big motorhomes the trans shifts to the lowest gear without overspeeding the engine when the ex brake is applied. I just used a relay so that when the overdrive soliniod was engaged the ex brake was open circuited .
Jim O