Not to hi-jack the thread, but some time ago I considered the GV and USG units. Came to the conclusion that taller tires would do almost the same thing for a lot less money. Running 315 tires and with the speedo recalibrated by the dealer, at 60 mph the engine is only turning 1900 rpm and at 70 mph it is 2200 rpm. Of course anything above 60 mph, the fuel consumption starts dropping, but depending on how I drive, I average between 19 and close to 22 mpg. Recently drove many miles at 50 mph and was surprised to see around 25 mpg.

 

Taller tires simply shift the entire gear ratio, of course... I wouldn't say being able to shift the gear ratio on the fly is "almost the same thing" as that. If one's only concern is dropping the gear ratio for the top end then, definitely, taller tires would do it. If you want to be able to retain the higher gear ratio (i.e. for towing, etc.,), be able to split gears at anything over 20MPH in order to run at optimum RPM AND get the OD on the top end, all at the flick of the switch - then tall tires alone won't suffice... you could do BOTH (tall tires & OD) & really stretch the legs at the top end.

 

Agreed that taller tires in effect only shift the entire gear ratio. This is a poor man's compromise. If I had the money I would go for a gear splitter and go down to 305 tires. The best of both worlds

 

I've heard not to put one behind an auto trans. Probably voids the warranty no matter what. Such a shame not to build a truck with the kind of gears you would like from the factory.

 

The G56 is geared so low, first is rarely used. Simply going to taller tires gets you an extra useful gear. With only the taller tires its feasible to run in 5th which is the direct drive, 6th being an over drive.

True, under/over drive gives you more flexibility, like a two speed rear.... and more likly will get you the driveline ratio you want.

 

True that. I'll be implementing a bit taller tires as well... after I get some good use out of the stock ones. I don't mind making additions but it's disheartening replacing* brand new stock equip. *essentially discarding, not much of a market for stock wheels/tires?

 

Bigger tires would be nice and I put 315's on my 02 with 4.10's and it would cruise at 2100 at 70 in OD on the 5600. On the dually, I dont like how the two rear tires would look sticking out the fenders. So I put on 265's and will be happier with what I have. If I had a single rear wheel, I woul have on 35's again. very happy so far.

 

Has anyone stretched their truck out on the top end yet with the GV or the US gear vendors unit?

 

Going to 315/70-17 from the stock (265/70-17) wheels effectively drops your axle ratio from the 3.73 to a 3.44 (if you have a 4.10 it 'drops' it to 3.78). Even for the older trucks with a NV5600 this is nice. At 70 mph my engine RPMS dropped from 2080 to 1915. by going to the bigger tires. Granted this is a 8% drop, not the huge 20% or 25% that you get with the gear vendors, but this ones free!

 

changing tires will only drop you maybe 100rpm's when the gv unit will drop you at least 500 and gear vendor says as much as 700rpms. they only offer one ratio. I did lots of research on the gear vendor and US gear units and found out there are some bad things about the gear vendor and the us gear unit. gearvendor does not recomend them for 6 speed towing aplications unless to drop the transmission to 5th gear which gives the same final drive ratio as your 6th gear was in the firstplace without the overdrive. seems its hard on the tranny and becomes completely inefficient because you are no longer running the engine in its sweet spot, 1700 to 2000rpm's. running at 55 -60 you will be at 1300 or so rpms and will have to mash the throttle down to keep up to speed. also I believe you automatic guys will void your transmissions warranty by installing the GV unit. automatic guys, you will also have to shut of the trucks standard overdrive when towing. (tow haul mode) also, the gearvendor has a hydraulic actuator to keep it locked in overdrive and if you come to a stop with the unit on or even go less than 25mph with the units hydraulic pressure drops to low and the internal clutch will slip and burn the unit up. I believe they have a safety switch that shuts the unit down on automatic aplications should you go below 25mph. I have also read that with the us gear unit the transition to and from overdrive isnt an easy one to make. have heard that some people actually have the units removed before they destroy them becuase they just cant get them to go in or back out of overdrive smoothly. this is why I bought my Mitchell overdrive. its a full synchromesh manually shifted unit and I could pick my own desired ratios, I can tow up to 35000lbs with mine without hurting anything because with the ratio I picked it only has a liitle more that half the overdrive ratio of the gear vendors unit. the problem with the mitchell is they dont manufacture them anymore because they didnt get along with computer controlled automatic trucks which is what about 80% of the new diesel trucks sold are. I found mine used in a 99 dodge and had mine completely rebuilt now by mitchell and it will be installed in a few weeks. just what I need, one more gear shift lever!

 

I have over 50000kms or 30000miles on my gv and I would not be without it I do not know where some of these Gear vendors experts get some of there Ideas Just call them or go to the web site It can be used on an auto as well as a standard without affecting the warranty when you slow down below 20mph and forget to shift it out of OD it will simply do it for you with out any harm to the unit. Yes it has to be wired so that when in 4x4 the OD can not be engaged (but who needs OD in 4x4. and it is not rocket science to wire it so the ex brake will not engage when in OD. I used a Pot relay that would open the circuit to the ex brake when the GV solinoid was hot . My only complaint is the frequent oil changes and I would like to see a larger sump. also there is a slight more amount of driveline slack.I do not care what size tires you put on it will not give you 10 usable gears on six speed truck.Mine is installed on an NV5600 and I can not tow in double OD above 60 degrees F
(the exhaust temp comes up) but I believe those with the new six speed could. I tried both the US gear and the Gearvendors before I made my decision and I stand by it . I heard that US gear will not fit the new 6speed do not know if that is true though.
Jim O

 

+1 (good 1st hand info)
Mine is also wired to not engage concurrent with the 4x4 or exhaust brake.

 

How much do they have to take off the driveshaft to fit the GV in there? I have the LongBed and have 2/split driveshafts! JB

 

all the info I posted on towing with a gear vendor unit came from gear vendor. you can call them as I did.

 

12.25" is the length of the drive shaft "tube" from the middle of the u-joint weld (12.5" to the yoke) to the cut... this is measuring the piece I had removed from my stock shaft 2006 G56 Long bed 4x4.

It's laying in my office so it was easy for me to measure.

They tell you how to measure the required new length in the directions ..