dra7

I have being reading about a trans add on the adds 4 more gears to the stock trans. It gives you a gear between each stock gear and two additional over drive gears. They are a bit expensive but I like the thought of having a lower overdrive for heavy towing and an additional higher one for when empty. It would drop my 70 mph RPMs down to 1670 from the current 2000. There is plenty of HP and torque at 1670 for an empty truck and would sure improve my MPG.
This is the link on the add on http://www.drivetrain.com/new_overdr...g3spdauto.html
Any one using one and do you like it?

Haulin_in_Dixie

If you are doing 2000 at 70, I don't think it will help mileage at all. Slow to 65 and you will already be at 1800, it is the speed that can improve it. 2000 is about where they like to run cheap.

BBWD

dra7:

Got the Gear Vendors unit on my truck. Installed it at 11K and now got 130K on it. It is a good overdrive unit (over 60 mph) and my rpm at 70 is 1500 in OD. The unit added about 2-1/2 to 3 MPG. As far as adding extra gears, on an auto it is good for an extra OD gear only when running empty on the highway. You can go directly to the Gear Vendors site. They have dealers all across the states that will install for you. If the unit ever needs to be rebuilt (I'm told they are good for about 200K miles) the exchange fee is $600 and they will have one on the way before you pull yours so there will be mimimum downtime.

Also, I belive that U.S. Gear also makes a unit. Might want to check them out also.

John (DH)

sherman

Interesting,I have looked into the aux trasmission guestion extensively and I can't find anyone that has increased mpg while loaded.With the cost of this addon at $3000.00+ installed, there has to be a substancial increase in mpg.

Sleigher

I have had the Gear Vendor in my truck for about ten years.
It is easily the best money I've spent on my truck or anything for that matter.
While I didn't see huge gains in mileage the comfort factor of high speed travel more than makes up for it.
The 4.11 gears in my truck made for high rpms at 65-70 mph, as stated before I now cruise at around 1700 rpms.
Long tows up steep grades allow another gear between 2 and 3 which mean the difference between 30 and 45 mph.
The place I bought mine from is called Unitrax (Anaheim, CA) and they service it for free as part of the deal.
Get one you won't regret it.

Peter

Haulin_in_Dixie

I have played with 55 mph on my truck quite a bit. I have the choice of 1600 rpm in 6th gear or 2100 in 5th gear. Running direct in 5th gives better mileage. For one thing each gear set removes a percentage of economy.

12PACK

I know you get more gears going this route, but for someone who runs unloaded most of the time, wouldn't it be alot cheaper just getting higher gears? Going back to 3.55's if it's an easy swap.

sherman

Getting better mpg at 2100 rpm in 5th over 6th at 1600rpm is a big surprise,do you have any ideas on this one.

4x4not

2100rpm is more into the "sweet spot" of the power curve, and therefore the engine isn't working as hard. At least in theory

sherman

I'm surprised the gear heads out there in cyberworld didn't jump on this one!

bigblock2stroke

its all about bsfc

Haulin_in_Dixie

Sherman possibly in Florida with no hills, all flat you might do better at 1600, but in fly over America, 2100 does not labor the engine in any way, it sort of floats over small hills where 1600 takes quite a bit of throttle to go up them. 1800 to 2100 or even 2200 is where mine gets the mileage. 55 has always been a problem with 3.55 gears and 32 inch tires. A little low in one gear and a little high in the other. My best mileage is achieved at 1800 at 65 mph in od. But where I have to slow down, the direct works better than the od. I do on occasion get into Nazioise, and Ohio and have to crawl around letting cars pass endlessly.

sherman

Will the 3.55 and the oversized tires contribute to increased drag,1600 rpm is not working for your set up when your mpg is better at the higher rpm.According to Cummins, theoretically the mpg should be better at the lower rpm,but in your case it is not.It sounds like you tow a lot and have played with different set ups.

Haulin_in_Dixie

I am not going to win this one so why pursue it. I will only say that if mileage is better at 1600 why not run 1400 that is where peak torque is. Every engine has a spot in the rpm range that it runs on the highway using less fuel. Too low and you are into the throttle more to keep it moving, too high and you lose also. Many on here will attest to 1800 to 2000 being that range on the Cummins. Running lower regularly, you beat up on the drive line, lug the engine, etc. Running low rpms in od on the nv4500 backs off the fifth gear nut. Mine never did.

What does Cummins say about lugging? If you can not accelerate at the rpm then you are lugging. Also each gear change costs fuel mileage. Direct is gear free with the only gears used the rear axle. Overdrive adds two more sets.

When I am running out of fuel, happens now and then, I drop to 53 mph at about 2000 and add like 50 percent to the mileage with my empty trailer. I made a load of cars from Atlanta after putting in new rear axle bearings. The rear needed to be broken in and I could not. I ran the load at 50 mph in direct and got right at 15 mpg.

Its your truck, drive it the way you want. I can only tell you what my experience is with my truck.

Superduty

"its all about bsfc"

Actually it is all about part throttle BSFC, but that is spitting hairs...

I wish these trucks had a 7 speed double over transmission.

4rth direct (LO, 1st, 2nd...)
5th (1st OD) about 0.8:1
6th (2nd OD) about 0.65:1, just low enough that one could shift from 4th to 6th. The ECM could even have a shift gate lockout like it does on the Z06, although people hate it...

The thing about this setup is that the engine could run 1500-1600 down the road empty and then use 1st OD when pulling. The present 0.73 is a compromise for both towing and empty. Here we are running down the road in a 7000lb pickup with a 600 ftlb engine reving at 2000 RPM.

A 0.65:1 with a 4.10 and the ability to split into 5th would be great.

What would be even better is if someone made 5th/6th a true spit via an auxillary gear set and the ECM shifted it electronically via an air cylinder. Eaton had a transmission for big trucks that did this. They called it the TOP2. I never drove one, but I heard it was slick. One could keep the the conventional 6 speeds and let the engine worry about shifting the OD gears. Of course I'd want to override the ECM...