I'm considering the gearvenders overdrive unit and would like to hear about any experience anybody has had (good or bad) with them. There expensive but it should give me better highway mileage empty and give me that extra gear between 5th and 6th when towing.

 

I've owned gear venders on earlier trucks wi a 5 speed. The OD is a .78 and would be essentially the same as your 6th gear. About the only use for a late model six-speed manual would be running empty, but the engine load level goes up so much it doesn't save much fuel. It will make your truck go really fast tho. My 98 3500 would do about 130mph in double OD-now that's scarey!! Running 2200-2400 is a good load range for the CR and total revolutions is not a factor with a Cummins. Even the 68 auto likes to be in 5th gear (.83?) rather than load up at low RPMs in 6th. The load level in 5th will drop 15-20% until you get above about 2100-2200rpm.
Rick

 

i dont know to much about your 6 speed but i can run 80 mph right about 2000 rpm's in my 5 speed. i've driven about 630 on a little less than 3/4 of a tank. 32 gals. im trying to had another 50 gal tank in the bed.

 

Interesting...i've heard of OD/UD units before from a friend and his was on a Manual F350, he was very please with his. I'd be interested to find out if they have a unit for the 2004.5 48RE.

 

I wish GV would offer a different OD ratio... 22% is a bit steep. I had a US Gear in my 01 which was 20% and that was about perfect. But US Gear won't make one for the G56... they say too many computer issues to deal with. Dangit.

I want one, but I'm not sure i wanna spend $3K+ on one and end up with no mileage improvement...

Rob

 

How about free wheeling or manual locking hubs?? Right up in there in the same price range as the OD unit. I was considering going the hub way since I have an auto tranny, VERY pricey!! Many, many miles to pay for itself. My garage guy was telling me about pulling the front 4x4 driveshaft out as a way to get better mileage. Anybody ever do this and did you get a noticable increase in fuel mileage??

 

That would make an insignificant difference in fuel economy.

 

Supposedly, there would be alot less hardware spinning, less drag - maybe a little better fuel mileage in a 4x4??

 

Search it and you will find a really long, good thread on here somewhere with lots of info from people that have them. I know I want one and will get one someday just so I can drive 75 or 80 on freeway when empty without turning 2400 rpm.

 

There's very little parasitic drag caused by the front ring & pinion and axles turning.

 

I have one on my 5.9 and I also have an edge box. These are real numbers. I have my edge set on throttle % so I can see how much my foot is in it. I get better mileage down to 55 mph in 6th with overdrive on. Right around 1300 rpms. Now granted, I am not putting my foot into it trying to pass other cars, just cruising. If I am at 70mph without GV on, I am at 28% throttle and 19% with it GV on. At 75 mph, 23% with GV on and 35% with it off. At 80 it is 32% with GV on and 53% with it off. My mileage has gone up at least 3-4 mpg. I have had it on for almost 1.5 years and have 22k miles on it. Never once has it hiccupped. I went on the scale last week and I weighed in at 25,400 with truck and camper. So no problems handling alot of weight either. So far so goo.

 

With the new 6 speed auto the rpms are super low on the hwy. At 75 mph I'm sitting on 1800rpms. Seems perfect but mileage doesn't get any better w/ the 6.7l. In town I usually drive around in 5th gear so I'm not lugging the engine too much. Basically, what I'm saying is that there is no need for one of these if you have an auto trans....

 

I put a Dynatrac kit on mine because I wanted the hubs and to get rid of the unit bearings. Plus I was in there already doing the ball joints.

I have not seen any measurable mileage increase.

Pulling the front driveshaft off is really a waste of time. You're still turning the front diff and that's where most of the drag probably is.


John