subspd

What milage increase on an auto should be expected?

Mcmopar

I had one in one of my old work trucks, I loved it. I pounded the truck to death, the only thing that did not break was the GV. I had 4.56:1 gears so it was a must!!

Big Nate

In these new vehicles with automatic transmissions and their lockup converters there would be a gain in mileage if the engine has enough torque to push the vehicle at a lower RPM without using more fuel. This means an engine that has lots of low-end torque and a flat torque band like a diesel could benefit. The down side is more transmission heat and heat build up in the auxiliary unit. If you have a little more heat but a long way from critical you are fine.

How much mileage depends on weight, engine condition, driving habits, fuel grade, terrain... and many other factors.

I need some detailed info I hope to get from this forum like:
What Overdrive gear splitting systems are available?
What vehicles do they cover?
How much torque can a stock converter hold before slipping?
What is the critical heat limit on transmissions?
Can the unit be in OD when engine braking?

Personally I am interested in 06 Dodge stuff but any info is welcome and hopefully other folks will benefit from this as well.

JohnInNH

I have a gear vendors OD in my 06 6 speed. I get over 3+ mpg increase and a huge difference in top speed (I think it's computer governed at 112 or so MPH)

Towing in 5th over actually lowers transmission temp. Being direct drive.

6th over is sweet 1750 rpm at 70 mph :-)


Cons: $$$ and fluid change required every 10K miles

Big Nate

Thanks for the info, which fluid are you talking about, the GV fluid or the transmission fluid or both?

JohnInNH

The GV fluid.

mitternocht

The oil in the GV unit needs to be changed every 10K miles.

morkable

holy,, how come so often I wonder

Kevin

Jim O

I have a gearvendors that I installed my self 53000kms ago (35000miles) as some one said when you wire it up through the 4x4 switch the unit will not work in 4 wheel drive. I also had to wire mine up so that the exhaust brake would not work when the gv is in overdrive. As Mitternocht said there is a friction clutch to give you reverse and some engine braking. Also someone said that you have to change the oil every 10000miles and that is true. I found that with my NV5600 I can tow in 6th over up to about 50 degrees farenhiet after that my exhaust temp comes up. I usually tow in 6th as it is about 250rpm lower that 5th over. I found about 2mpg difference bobtailing but I have not noticed any increase in milage towing, but I know that the ability to split gears makes it so you spend less time on the hills.
What I like is 1650 rpm @ 75mph. To be able to go down or up one half a gear.
what I do not like is the cost of the unit, the 1350 front u joint appears small to me ( the the driveshaft people that shortend my shaft said it was ok) and you have a little more slack in the drive line and you have to change the oil in the unit frequently and it is expensive as well as inconveniant.
would I do it again you bet. It is very nice to have with a NV5600 it is a must with a G56.
Jim Otto

JohnInNH

It only holds a quart.

Use GM #1052271 SAE 80W-90W, API GL-4 Rear Axel Lubricant or Penzoil #409 SAE 80W-90W, or GL-1 Mineral Gear Lubricant

From page 41 of the GV manual.

(The 4 at the end of the GM # was a typo. Edited for typos)

Note... Updated info from GV for synthetic is GM 12346190 + Mopar 04874459

Big Nate

Jim O, you mention towing in 6th and over, do you have any more info on this?

Flat terrain?
Trans temp.
Load weight.

Thanks

dieselengineer

Does anyone have feedback on an US Gear overdrive unit?. Is there the same backing issue with this unit?

Jim O

The Oil recommended by GV is GM 12346190 or Mopar 4874459 or Castrol Syntorque. These are Synthetic Gear lubes, they say you can use GM1052271 not 1052274 like JohninNH said but it is not a synthetic and will result in harsher shifts And if you have the towing sump (like you would have on a truck right) it holds a litre and a half not a US quart or .946 litres like John says. The GM synthetic is Twenty one Canadian Dollars and some cents and the Mopar synthetic is within pennys of the same price. I have not been able to find Castrol Syntorqe in Canada but I am now using Amsoil MTG it was just recommended to me by Gear vendors and By the way they do NOT recommend Mineral oil at all. So I stand by what I said before It is an expensive oil that is required and although there is not much of it it is an inconveniance to change it every Tuesday and Thursday.
Jim O

Jim O

To tow in OD it has to be fairly flat but if you watch the Pyro you can get away with it on some grades. As for trans temp I have a NV5600 and do not have a guage on it. the Gross weight with the fifth wheel trailer is 20500LBs. I have a 3:73 ratio and If I had a 4:10 I could tow in 6th over most of the time but as I said the exhaust temp comes up over 50 degrees ambiant temp (farenhiet) at 60 mph If I run 70 MPH the exhaust temp is cooler but I use a lot of fuel. My trailer has a high front Bedroom and moves a lot of air.
Jim O

mitternocht

Yea, I noticed that on cold mornings even running empty the Cummins will warm up rather nicely as soon as you get into 6th over; well faster than running in just 6th.

I’ll have to check the manual to say what it says about engine braking with OD on/off.

I guess the worst thing that would happen while going in reverse is that the clutch holding the ring gear could slip putting you into “reverse OD.” I’m not sure how much torque that would take. The unit is good for 30K LBS gross recreational, 25K LBS commercial, 1200 HP and 4500 Ft-Lbs torque (forward Spike) so I’d think it should handle backing up under normal conditions unless you are trying to pull out a stump in reverse with your Crazy Larry or something.