prlsnpsdodge

I got to thinking the other day , while paying $3.25/ gal for diesel... What else can I do to drop my RPM's. Keeping things close to stock, or at least using readily available parts - how can keep the regular ratios and still get lower highway rpms like the Gear Vendors unit, but without the high price tag..

So I started thinking, since a transfer case lowers the total output after the transmission, what would happen if I flipped it around and reversed the gearing... so to speak. I know that in a transfer case the gears can be changed out for serious offraoding vs just stock gearing for 4wd, so why can't the gears inside the unit be switched to go from lowering the ratios to raising the ratios???

I realize there are hurdles to overcome and such, but it's the same principle, Right?

and to further complicate things... I would be adding this (if i could get it to work) onto a 2wd truck.... but just the transfer case. I'd block the front driveshaft output. WAAAY too much trouble to add a 4wd to a 2wd... Plus i dont really need the 4wd in my normal driving.

Lemme know what ya'll think.....

Backwoods Bumpers

interesting idea. I think the main design problem would be strength of the compontents. Any time you have an O/D, you have a big gear driving a smaller gear, which is hard on the components, especially a chain drive setup like our t-cases

prlsnpsdodge

ok, so I did some internet looking, and I found a Drivetrain website that specialized in rebuilding Transfer cases and such. They also sell the GearVendors units, but that isnt why I called. I spoke with a fella in the support department about my idea- but he was a little too hurried to let me go into detail.

What I gathered from the call was switching the gears out would be harder to do then just flipping the unit around. He did suggest an NP 205 model due to it being self contained. And he also said that he had heard of it being done before... That's a least a positive step towards better mileage. This would accomplish mostly the same thing as the GV unit, but without the gear splitting. On my 1970 Dumptruck, I have the Hi- Lo option built into the transmission. I am trying to do the same thing just with a drop in unit after the transmission.

rockcrawler304

In theory I'm sure it is possible. You have to remember that all t-cases are set up to have the 2wd mode be a 1:1 so if your transmission OD is for example 0.85:1 that is also the same output of the t-case. If you drop the t-case final ratio to say 0.85:1 every gear ratio in the transmission will also drop by 0.15 including the OD. Not sure how this would affect your day to day driving and how the tranny will like it.

As far as having the gears made, any shop with a good gear hobber and knowledge of transfer cases (Atlas comes to mind) can do the math and grind the gears for a transfer case but you will need to pay for the R&D and the one off set of gears. I'm sure that cost would be pretty high.

Keep us posted with what happens!

wap

I am all about innovation and trying to new things but I can just about guarantee you that by the time you got a prototype of your idea you could have purchased a GV, not to mention all the time in R&D and other parts you would need fabbed up.

I dont mean to discourage you but chances are if you are that serious about dropping your RPMs you would be much better off, in both time and money to either get a higher R&P gear or do the gear vendors.

Good luck

Nsomniac05

I saw another O/D unit a few years ago that mates to the transmission instead of the trasfer case. I think it was axletech or something along those lines. It could either be used as an overdrive or an underdrive. you might research that. I can't speak for their durability under 1000+ lb/ft of torque though.

etn550

Forget the transfer case idea. It would be a one off the cost would be very very high, probably well into five figures.

Even the "production" off road cases are not cheap.

Gear Vendors is about the only option left to buy straight out. All of the new 6 speed automatics are getting big overdrive and low starting gears. The need for GV will taper off. They were invented for 3 speed automatics with no OD.

I had a GV in a '96 12 valve. It was ok but they are not high mile units. Mine failed at 150k Many fail at 70 -80k. It did match wel to the NV4500 5speed. Made for 7 well spaced forward gears. The GV is a terrible match for the NV5600 or G56 because the OD ratio is the same. Can't split gears.

I also had a 6.9diesel ford PU with the T19 four speed with 1:1 top gear. I put a 6041 Spicer (I believe that is the designation its been 20 years) 4 speed auxillary behind the T19 4 speed. These old auxilaries were originally for gas powered tandem axle dumps and such. It had 2.1 granny, 1.2 under, direct, and .86 over drive. Talk about splitting gears! This thing let me have 3 gears at 65 mph. Wound out tight at 3300rpm in direct/under for power and hill pulling, direct, and direct/over for light cruising. I could do a 3 way split in the low gears and two way in top gear. It is a true truck tansmission so it was not synchronized meaning shifts were easy and fast with no clutch. Made a big difference in towing and economy and noise. It has it's own stick so with 4X4 i had 3 sticks in the cab! This trans was called divorced, meaning it had a driveshaft in the front and a driveshaft out the back. I positioned it near the center carrier bearing and replaced my two piece driveshaft with two separate shafts. had some R&D to get the alignment and harmonics right but my friend that bought it still has it with 350k on it now.

I wonder about using a 10 speed Roadranger in the CTD. They have a 10:1 first gear and .78OD so with a 3.42 axle they might be pretty good. Plus they have 2 speeds in reverse which is great for backing a trailer in creeper mode.

bkrukow

THis never works for me but here is a Chevy with a Cummins and a 10 speed.

Some one will have to fix this mess for me. I for the life of me can not figure out how to embed a youtube video.

<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/2CG0Yx3cmsc?fs=1&amp;hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/2CG0Yx3cmsc?fs=1&amp;hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>

Raspy

It's a complete waste of time for efficiency, practicality and mileage.

You can't keep lowering RPM and increasing mileage, your system would have more parasitic losses and the ratios are way off from what's driveable.

No matter what you do, a certain amount of power is required to move your truck at a given speed. Adding more gear boxes INCREASES the parasitic losses. Lowering the RPM only helps if it was already too high.

Test the theory for yourself and report your findings. Drive along a test section of road at about 50 MPH. First run this stretch in third gear (48RE direct) and with the converter locked. Reset the computer and record the mileage over a specific range. Then run the exact speed and conditions on the same stretch of road in OD lockup and see what the improvement is. The only difference will be an RPM of .63 of the first run. What's the mileage difference?

Concerning your extra transmission and all the hassle and extra parasitic losses.......A fun project, yes. Practical, no. Better mileage? not.

prlsnpsdodge

Well... I appreciate the insight... I was just thinking and trying to find a way to get 143/ MPG at 85 mph while towing 15,000 lbs uphill both ways in the snow!!

Guess I can think up a nother project that's a little more feasible and try and not break anything in the mean time...

Happy New Year and Thanks!!

rockcrawler304

Here ya go

Jim O

Sorry but you are wrong, the GV is not a bad match for the NV5600 The Nv5600 has an OD of .73 and the GV is .78 I will admit that there is only about 50 rpm between 4th over and fifth but all other splits are pretty good. The early G56s were .78.OD but I heard 07 and up they fixed that. I have slightly less that 150,000miles on mine but the fellow that recommended Gear Vendors to me has run his on a Ford for 390,000 and then bought a Dodge and he told me for $850.00 US. he got a factory exchange unit to fit his Dodge. He pulls RVs. from Indiana into western Canada. His reason is fuel economy and the ability to use double overdrive when he is running empty to Indiana.
Jim O

etn550

Sorry, I stand corrected on the NV5600. It is a different animal than the G56 and I have not drove a 5600 with a GV or split the ratios on paper to see how good a match it is. The new G56 is .75 od so not really much of a difference to the old G56 at .79. I mean yes it is noticable but when the OD is a .78.... The old Spicer box I had on the ford was .86, a true 1/2 gear.

I really really wish GV would make a ratio between .82 and .86. Their choice of .78 was perfect for the old 3 speed automatics and the old 4 speeds, especially the ones with granny 1st. That was 30-40 years ago. They really need to update!!

As far as the GV, I lived with mine a long time did a ton of preventative maintenance on it and when it failed it broke the main shaft at a stop light starting out at a light load. I got a replacement exchange from GV for $750 plus the old one returned as a core even though it was toast. It is just a quirky design the way it works and the limitations it has. It is fairly lightly built and the gears in it are not very impressive. It cannot take any exhaust braking except in OD /OD or it slips. I did not exhaust brake in GV OD. Never the less it will split the gears that need splitting perfectly in the NV4500.

It is a good option to get better mileage if you are not already in the proper rpm range when running. I had it on a '96 12 valve dually with the small stock tires and 4.11 gears so, yes, it made a huge difference. GV's 30,000 GVW limit is unrealistic when it breaks towing 20,000 and less on the average. And their torque breaking strength is meaningless in the real world. The fact that mine was a fatigue failure of the main shaft just points to over stressing the components. My failure was not related to the overdrive function. A more common failure is the quirky cone clutch material burning up. That failure mode in my opinion is totally preventable. There are some sprag clutch failures as well, which is an OD mode overload or fatigue failure. I did not tow anything outragous and I always had the GV brainbox properly hooked up so that it would only shift when it made it's required 600 psi oil pressure. Changed the oil in it a lot too. GV also used telephone plugs to make the brainbox and shift mounted switch connections. The phone jacks are not designed for vibration io a vehicle environment.

I'm just trying to give a perspective from my personal experience. I would consider another if I needed the gear or if it could really be used to split effectively.

But there is a huge huge difference between running a 6.9 NA ford at 175 hp and a modern Cummins with a smarty at 390hp plus. Keeping the ford 6.9 at it's peak power and making 200rpm splits with the 4speed splitter box gave performance improvements that cannot be imagined. It was like night and day! But a high hp high torque Cummins does not need the splits, it can pull 750 rpm between shifts with ease. Plus, for real towing 300Hp constant will overload the cooling system on a hot day anyway.

From what I found on the discussion boards the life is short. Like I said I did get 158k out of mine and i was careful with it.

Jim O

I agree with etn550 about the old style brownie trans. they also had a two speed that your could swap the gears around and go from direct and over to direct and under. and the shafts were about 1.5 inches in diameter and the engine in front of them was a Ford flathead or a Chev or Dodge Six with less than 250 CID. and probably less torque than our Cummins put out at Idle. I also agree that the .78 ratio is not perfect and .82-.87 would be much better. The GV is a high maintainance item I fabricated a sump that doubles the oil capacity and I change it at about 15,000 miles. The exhaust brake does work when the GV is not in OD. and that is how they tell you to wire it. When my GV is in OD the Ex brake will not work. Also when I am in 4x4 the gear vendors will not work the way it is wired. I was disappointed when I got the GV when I saw the 1350 Ujoint on the back of it as the Dodge comes with a much larger 1480 but I had to change the 1480 on the back of the Driveshaft and the 1350 is still good. The 1480 had aprox 12,000 miles on it when I put the GV in the truck but I have passed that mileage with the 1350 by over 30,000 miles and it is still good. I looked around for the old style brownie but when I could not find one I bought the GV.
Jim O