Gear Vendor swap

[Jurek]

I am thinking about swaping GV from TH 400 to 97 2500 4L80 trans./2wd/. What do I need to change/ splaine sleeve coupler for shafts connection, main cupling adapter? Can it be run without 2nd VSSB? Whats happen with lock up conventor speed when I shift from overdrive to the 2nd over. I plan to use it as 2nd overdrive only. I know I have to shorten the driveshaft. I have 3.73 in the rear and 285/75/16 , getting about 16/17 hwy mpg. Can I get better with 2nd overdrive. I have Kennedy 3,5 exaust with down turbo pipe. Any opinions. Thanks.

[Edahall]

I doubt you will get any better fuel economy running a double over drive with the setup you got. You might even get worse since you'll be below the torque band on your engine which I'll get into later. The only reason I can see for doing it with your setup would be to lower the engine noise or to take the strain off your transmission. If you do a lot of heavy towing, you could extend the life of your 4L80E transmission by towing in 3rd (direct drive) and using the Gear Vendors to provide over drive. If you read my signature below, you'll see that on my 1990 Suburban I've got a Gear Vendors, 6 speed manual, 3.73's and the same size tires as you. At 65 and with double over drive, my Cummins engine is only turning over at around 1400 rpm's. However, the difference is the Cummins puts out its power lower in the rpm range compared to a 6.5L so it works out fine for me and on top of that, it greatly lowers the engine noise in the cabin. When I tow, I use direct drive on the NV5600 and use the gear vendors for my over drive. It should take a lot of the wear and tear off of this expensive transmission. With your setup, I believe the double over drive would lug the engine. You might think about changing to 4.11's or 4.56's should you decide to install the Gear Vendors.

[Jurek]

What mpg do you get on your suburban. I always like to heve a cummins but end up with 6.2 and 6.5 gm diesels. How hard was to stick cummins in to the chevy, was suburban diesel to begin with.

[Edahall]

What mpg do you get on your suburban. I always like to heve a cummins but end up with 6.2 and 6.5 gm diesels. How hard was to stick cummins in to the chevy, was suburban diesel to begin with.

To be honest, I have yet to measure the gas mileage. I'm planning to take a 6000 mile road trip in another 2 more weeks so I'll get a chance to measure the fuel economy. I'm hoping that I get low 20's. I have wide 305/75/16 tires and a 2 inch lift which is not good for mileage. I don't expect as good fuel economy as my 82 6.2 Suburban which would consistently deliver 30 mpg. The 6BT Cummins is kind of an overkill as far as moving this vehicle solo down the road. Even when towing a 9000 lb trailer, I never even had to drop it out of overdrive pulling up a 6% grade. A better match if fuel economy is your main objective would be the Cummins 4BT. People are reporting as much as 35 mpg with this engine in a full size truck.

The Cummins fits right into the truck like it was meant to be there. There is plenty of room in the engine bay and I had no clearance issues. The trick for doing this retrofit is to do your research and buy all the correct parts and components before beginning the project. One issue is weight so a tough front end is needed. Turns out a solid axle works out better under the weight of this engine.

[GMC Hauler]

To be honest, I have yet to measure the gas mileage. I'm planning to take a 6000 mile road trip in another 2 more weeks so I'll get a chance to measure the fuel economy. I'm hoping that I get low 20's. I have wide 305/75/16 tires and a 2 inch lift which is not good for mileage. I don't expect as good fuel economy as my 82 6.2 Suburban which would consistently deliver 30 mpg. The 6BT Cummins is kind of an overkill as far as moving this vehicle solo down the road. Even when towing a 9000 lb trailer, I never even had to drop it out of overdrive pulling up a 6% grade. A better match if fuel economy is your main objective would be the Cummins 4BT. People are reporting as much as 35 mpg with this engine in a full size truck.

The Cummins fits right into the truck like it was meant to be there. There is plenty of room in the engine bay and I had no clearance issues. The trick for doing this retrofit is to do your research and buy all the correct parts and components before beginning the project. One issue is weight so a tough front end is needed. Turns out a solid axle works out better under the weight of this engine.

I wanted to contact you directly, but your profile does not allow private message.

I am interested in this swap. I am not going to do it now, but a few years down the road after I get my money out of the 6.5. I want to put the 12 valve in and the NV5600, no GV needed.

My current vehicle is the 96 2500 4X4, 8600GVW (heavy rear axle version).

Any additional info you can provide, if desired, in a private message, would be appreciated.

[Edahall]

Here’s some pictures of the swap posted in the following thread:

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=36921

I also enabled my private messaging.

The NV5600 is a nice transmission because of the close ratio. With this transmission, you always have the right gear no matter the situation. The NV4500 is much cheaper to buy but the space between 3rd and 4th gear is super wide. You have to run the engine just about to the governor before shifting. Also, they are not as strong particularly in O/D.

[Edahall]

What mpg do you get on your suburban. I always like to heve a cummins but end up with 6.2 and 6.5 gm diesels. How hard was to stick cummins in to the chevy, was suburban diesel to begin with.

For those who are interested, my 1990 Suburban with the Cummins returned 25.5 mpg on our trip.

The 5000 mi road trip started in Los Angeles CA and went all the way to the southern tip of Texas then to Houston then northwards to Columbia, MO then through Cheyenne, WY and back to Los Angeles. The Cummins engine and 6 speed manual transmission combination performed flawlessly. I kept my speed at a conservative 65 mph for most of the trip and I used my foot rather than cruise control. I used 2 cycle oil in the fuel which I heard helps slightly with fuel economy. The wind throughout the trip was not in my favor. I had strong head winds for most of the trip. The engine was very happy running at 1400 rpm’s at 65 mph with double overdrive from the NV5600 and Gear Vendors and had enough power to pull itself over most of the hills without downshifting.

Overall, I am very pleased with the setup. My 82 diesel Suburban got even better fuel economy but had much less power and was a ½ ton 2 wheel drive model. I believe with narrower tires rather than the wide 305/75/16 tires, I will be able to match the fuel economy of my 82 Suburban. Lowering the vehicle would help as well. It now has a lift kit on it but I’m looking at the possibility of installing an air suspension that would not only improve the ride but be able to lower the truck while on the freeway for less wind resistance and better handling. For the whole trip, I spent about $600 on fuel and the lowest price for fuel was found in Harrison Arkansas for $2.70 followed by Kansas City MO at $2.74. The most expensive place for fuel by far was California at $3.17. I used Gasbuddy.com to find the lowest prices on fuel which saved me probably around 30 cents per gallon.