"To overdrive or not to overdrive, that is the question."

[GLack]

I have a 2005 2500 short bed 4 door p/u with the 5. 9 ltr. Cummins. It has the 6 speed manual with the "tow package" and 4. 11 rear end. My question is for any opinions and facts anyone might have on putting a "Gear Vendors" O/D unit on this vehicle. The eng is at 2500 rpm at 70+ mph and I would like to lower that to improve MPG.

Soooo, any opinions on or personal experiences good or bad with a Gear Vendors unit? Are they worth the $4000 bucks? Do they last? Is it a good company vs. any other comparable products? Do they stand behind their products? OR... . should I just put huge tires on the truck? Is changing out the rear end to a higher gear ratio cheaper?, overall better? Can I even put an o/d unit on my set up and not end up causing other problems in the transmission? I don't really tow anything, (don't ask me why I bought it with the tow package cuz I would have to say I was ignorant at the time) so my biggest concern is if I did put one on and I did tow something, how compromised might I be making the eng (?) or transmission (?) or... ... (?)

Is it worth the money vs. the potential fuel savings vs. wear and tear, if any? Genuine experience with Gear Vendors would be very appreciated. Thank you.

 

[HBarlow]

Personally, I think it would be a bad way to spend your money. I don't think the GV units have the strength to handle the torque of the mighty Cummins engine working against a load.

IMO it would be cheaper and wiser to change the differential gearing.

The bigger issue is, will reducing engine rpm actually save fuel? I think the answer is not much. With a gasoline engine it definitely would but I have my doubts about saving fuel with the Cummins. It would make the cab a little quieter.

 

[Hoefler]

What little fuel savings you might get will never pay back what you have to pay for the gear box and install.

 

[Regcabguy]

Consider a 285-75-17 tire. It's 34" tall and fairly skinny and should alleviate the high freeway rpms without killing your fuel economy.

 

[goodguys75]

Consider a 285-75-17 tire. It's 34" tall and fairly skinny and should alleviate the high freeway rpms without killing your fuel economy.

thats what tire and wheels i run... about 69-70 i am a hair under 2000rpm... . anything over that the fuel milage plumetts... .

 

[Fistfull]

I have a friend with a GV OD in a 96 2500 with a NV4500.
Two things, oil has to be changed often and it will not withstand shock loads.
He loves it though, 80 MPH and less than 2000 rpm... yea 3. 45s

 

[jelag]

I sold gear vendor for 15 years in the business that I owned... I suggested it for customers that needed the gear ratios for towing... or for better cruise speeds as you can get a gear vendor as an overdrive or under drive... . Because they use a cone clutch and transmit power on direction very well, they don't recommend them with the use of exhaust brakes..... We never had a warranty issue with them... and more than often helped customers who went looking for them in a junk yard and wanted to refit them to their vehicles... . and they really handle 15-18K lbs...

But not once did I ever promote them as a way to increase mileage... nor should you expect better mileage... from a mileage standpoint the investment will never pay unless you drive 60-75K miles a year..... its just not there. .

 

[TLane]

I had a Gear Vendors on a previous (Ford) truck. On that truck, they could not put the unit on the back of the transmission (ZF-5 manual), so they installed it in place of the carrier bearing.

Things I liked about it:

1) Being able to split gears and get pretty close to "optimum" engine RPMs.

2) Other people drool over it.



Things I didn't like about it:

1) Replacing the carrier bearing is a bad idea. The front and rear drive shafts are "synchronized" so the u-joints work properly. Putting an gear box there alters the sync, so when it was in direct drive I'd sometimes notice driveline vibration. I'd put it into O/D and then drop back out, and if I'm lucky it would be back in sync and the vibration would be gone.

2) You can't use it for engine braking in first or second gear. I missed that in the owners manual and got a nasty surprise towing my travel trailer down from a pass with switchbacks - the unit dropped into and out of O/D with quite a bang.

3) I had a shift solenoid replaced under warranty. Good news: the unit stays in direct drive if the shift solenoid doesn't work.

4) The unit started leaking oil around the shaft seals after about 40K miles.



I let the unit go with truck. On my next Ford, I wished I had kept it, bought adapters and new seals and put it on the next truck; but only because I had already paid for the unit. Now that I have a Dodge with a Cummins, I don't need it.



There is a competing unit made by US Gears; it uses more of a manual shift mechanism and might be better. I haven't had one of theirs so I don't that much about it.



My advice: either get bigger tires or change the rear end ratio. I think the rear end ratio can be changed for around $600 to $1000. I'd recommend 3. 73 ratio. Don't forget if you have a 4x4 to change BOTH axles.

 

[gsbrockman]

Are they worth the $4000 bucks? I don't really tow anything, (don't ask me why I bought it with the tow package cuz I would have to say I was ignorant at the time) Is it worth the money vs. the potential fuel savings vs. wear and tear, if any?

2005 was a split model year for six speed manual transmissions. I *assume* since you've stated the truck has 4. 10's that you have an NV5600 (reverse up & to the right; cast-iron giant). If your truck is indeed a G56 (reverse down and to the left) it has 3. 73's as 4. 10's were not offered on early model pickups.



$4k is a huge amount of money..... and I'd try 35's on the stock wheels for some rpm savings first. As already stated... ... the marginal money you'd save with and without a GV Overdrive would take forever to recoup.



Greg

 

[jelag]

This has made me think and poke around... I've found both sets of gears, to change both the front and rear for only $800 for the 2 ring and pinions... which is what I would do if I thought it would pencil out... . There is a 3. 42 set available for the same axles used in the GM products... On my 3500 dually with 19. 5" tires that would make my truck turn 1790 rpm at 70 mph... but the speed in 5th is too high if the truck won't pull the trailer up a slight grade... a few trade off's... .

I did email the manufacturer last night with the hopes of getting their input... of course this is a project that I've done in the past and can do again. . so their be no labor but a couple of hundred in new oil and I'm sure something else either on the way in or out. .

 

[Sean Flanagan]

Here ya go... (doing this from my phone. Sorry for typos and other weird stuff)
I have a GV unit that I picked up from a wrecked truck for $500 with adapter and drive shaft a couple years ago. It was a steal! I sent to to gear vendors for a rebuild. Another $500 later I was good to go.

I love this thing. It works better than expected. Let me tell you ,it is the only thing I have done that has any real economy gains. BI have tried a few things to*improve the economy... To get where my old '98 was.

Edge box, more power yes, makes the overhead meter lie even more, no noticeable mileage gain. Had to buy a new clutch...
Bigger tires, nothing other than screwing up the speedo. *If anything it is worse.
** Smarty, maybe 1/2 mpg and too darn much smoke at the altitude I live at. * More power, yes. *Lower EGT, yes. * Good thing I got a new clutch.
Air filter gizmo... Nothing except more turbo noise.
Exhaust. *Nothing but droning noise. *Sold it and put the old junk back on.

Gear vendor: A solid 2 mpg increase or more. *Under some circumstances, I can break 24mpg, but it is rare. *Before GV, I was at 19 back and forth to work, now 21 or 22. *And that is no bull hand calculated. *

I have had it for 60k miles and it still works as good as the day I got it. * I do change it's oil every 10k, *but that is a piece of cake. * Bought the oil from Amsoil.

High points: *
Real mileage gains!

1600 rpm at 65mph. *

Super quiet cruising on the highway

Fairly easy install.

It is tough despite it's small size. *I have flogged the thing. Edge box on max during acceleration and drop it into OD without the clutch. *Woosh! *No slipping or shudder. *

low points: *
can't use it in 4wd, which is ok because I don't go fast in4x4 anyway.

Shift is very firm. *While you really don't have to push in the clutch to shift, I do anyway or it is quite a jolt.

Because of the close ratio of the G56 it can't really split gears. *It is more like a 7th gear. *The GV is a 20% overdrive.

If you are going to use an exhaust brake, *you have to turn the GV unit off. *Their little brain box will do it for you so it is not a worry. *I turn it off when I gear down on a*hill anyway.

Getting the drive shaft angles right was tough. *Takes a lot of trial and error to prevent drive line vibrations.

Peak economy gains are on flat ground, unloaded, at 60-65 mph. *The gains drop the faster you go, and if you are towing, and if the hills get big.


*I tow a 26ft travel trailer with a boat behind that in the mountains of Colorado in the summer and a trailer full of snowmobiles in the winter. *I don't baby my truck.

I commute 60 miles round trip
to work with 60% highway, 40% city.

There you have it. * Would I pay full
price for one? * ... . Maybe... **

 

[JMarketos]

I have a 2005 QC 4x4 auto with GV unit installed, works great.

I disagree with HBarlow's speculation about GV strength- just read up on them, you'll find they are installed along with OEM eqt. in motorhomes etc. I have relatively few miles on mine (a few thousand). So far, I can say it has performed flawlessly. Search my other posts if you want, I have written in some detail about the GV.

I echo the other replies above- yes the GV will probably improve your fuel mileage, but you probably won't recover the cost of the GV install in fuel savings. I installed my GV to improve towing RPMs because (with the auto trans) 4th was too stiff and 3rd by itself was way too low (high RPM) for towing at highway speeds. Towing with the GV, I run in 3rd gear with GV engaged and RPMs are ideal. Towing MPG improved significantly with the GV, that's because the engine now runs in a better area of its efficiency range. My main reason for adding GV was to improve the high exhaust temps that resulted from running the engine in high gear, at relatively low RPMs and high boost. Yes I have also found that I can run the empty truck in high gear with the GV engaged, engine turns around 1500 (3. 73s, stock tires). That does result in improved MPG but again the break even point on ROI would be wayyy out in the future.

Like you, I also considered changing axle ratios. Although cheaper than GV, it's still significant cost especially if 4x4. And proper setup of gear pre-loads and teeth alignment requires someone who knows their stuff- many people just prefer not to mess with a properly working stock axle.

A shiftable unit like GV offers the ability to change ratios = flexibility. Changing axle ratios or changing tire size offers a step change, that remains as-is. That might leave you better off overall when empty, but you might find yourself limited if you ever have to tow anything relatively heavy. It's a tradeoff of $ vs flexibility. Frankly, my truck isn't driven many miles these past few years, so I'm not getting much utility from the $ I spent even for towing. But personally, I don't regret doing the upgrade. (Reading between the lines here, what shows through is: the original auto manufacturer really needs to provide a wider range of available trans gear ratios; IMHO that's still true today... )

When I was researching purchase of my GV (mid 2007), contacted also US gear. Person I spoke to told me they no longer manufacture the OD/UD unit (which would be competitive to GV).

Given your indication (not towing much etc. ), your most efficient route might indeed be a move to larger circumference tires. But be careful there too... if the new tires have more side wall flex and / or wider tread than the present ones, those characteristics will have a negative effect on MPG. Good luck !

 

[rscurtis]

How about simply upgrading to the later gearing in the G56, assuming you have that transmission with the early overdrive ratio.

 

[RustyJC]

Because of fundamental design differences, I'd suggest the U. S. Gear unit is a better application for manual transmissions while the Gear Vendors unit works better with automatics.



The U. S. Gear unit is an adaptation of the old Doug Nash OD unit which used components from the Ford T&C top loader 4-speed transmission. Being an all-gear unit, it can be used with an e-brake, and there are no minimum speed limitations on its engagement.



The Gear Vendors unit is basically the old Laycock de Normanville overdrive unit design as was applied to Austin-Healey, Triumph and MG back in the 50s and 60s. As was mentioned earlier, it isn't compatible with an e-brake since it transmits torque much more efficiently one way (from the engine to the rear axle) than it does the other (from the rear axle to the engine).



Rusty

 

[kscheffler]

I've had my GV for 90k miles and never had a problem change oil every 10k. I have kep fuel records since new and the GV on average will increase fuel performance about 1. 5 mpg but on flat roads it can be as high as 2. 5. The noise reduction and flexibility is wonderful. I would do it again without a doubt. The only down side is not to use exhaust brake but just turn it off and switch the brake on it is not a big deal. They have an auto disconnect function for the exhaust brake anyway. I don't tow heavy very often 10k; but do have some 1600 mile trips and it makes it a dream to go down the interstate at 78 mph at 1900 rpm; I have oversized tires to go with my 4. 10.

 

[GLack]

I would like to say thanks to everyone for giving me lots to think about on the Gear Vendors O/D question. A lot of excellent ideas and opinions based on logic and experience. I have a lot to think about and if anyone is interested I will post what I actually end up doing. Again, thank you for all the insight and experience.