Changing the Transmission for better mileage

You ask a good question. The thing that you would possible benifit from the most is maybe a taller rear axle ratio as you have OD now and a different tranny is not going to help much. Also your Dakota is a lot less areodynamic than your car and front wheel drives have less power loss in drive train too so it will never do as well. A few tips, remove or lower tail gate on highway, run stock tyrp tire of 75 or 83 profile with smooth tread at or near max pressure as this will reduce rolling resistance. Also change lubes in tranny and rear axle ans fresh changes can improve MPG a fractio or more if they were overdue servicing. Waht axle ratio do you have in truck now?

----------------- The SnoMan

There's very little you could do to the trans that would improve fuel mileage AND be cost effective. It shifts up early to OD in an attempt to obtain better fuel mileage, so you want to leave that alone. Take a look at the rear gear ratio. Changing up or down MAY get you better fuel mileage, and it may not. You want the engine to be just starting in to the power band at your normal cruising speed - that's where it's most efficient. But again, it's probably not cost effective unless you plan on putting another 80-100K miles on that truck. There are a lot of other small things you can do to improve fuel mileage. Close the tailgate. Lots of tests and studies have been done proving that with the tailgate down you get worse aerodynamics and more drag. A tanneau cover is even better. Eliminate weight. What are you carrying around that you don't need? Evaluate your tires. Off road/all terrain tires create a lot of drag. And they are heavy, which requires more torque to get them moving. Pick a good street LT tire, and watch the inflation pressure like a hawk. Synthetic fluids are said to help. But I've got to say I have never noticed a differance in my truck one way or the other. But with that many miles it will extend your maintenance intervals, so it might be worth it to you. Finally, evaluate you driving habits. That will get you the most bang for the buck.

the tail gate down has been shown to increase drag in wind tunnel testing.

Changing the diff ratio would be much simpler and cheaper than the trans. Get a lower numerical ratio (longer legs) for better mileage and reduced towing capacity/torque.

Not true in real life with most pickup trucks. Gate down, or off (possibly better than down) reduces wind drag and increases highway mileage on just about any pickup I've driven (and that's a fair number) A mesh gate (almost equivalent to none) can be used if you occaisionally need to carry something that could otherwise fall out.

I question that a lot because I have seen first hand otherwise. Even my 2000 K3500 pickup up about 1 MPG with gae dow verse up when I made to 240 mile round trips two days in a row, same weather and speed to same place. Having worked inflight test R&D for many years in the past I know how easy it is to do the same test with different varibles and have completely different outcomes and a wind tunnel is not the same as moving down the road with truck generating its own heat signature which expands the air under truck and changes the parameters.

----------------- The SnoMan

Tkae a 300 mile trip with gat up and one with gate down and I gaurentte that you will see a fuel consumption increase with gate up because fore reasons I posted earlier, the wind tunnel test does not bear fruit properly.

----------------- The SnoMan

I can't speak for you and the trucks you drive.

But I've seen a lot of tests done against wind tunnels and water flow. Gate up was always better. Also, I tested my own truck. Worse was gate down and bed open. Slightly better with bed open and gate up. Even better still was gate up and cover on. My own tests seemed to follow the mentioned test results.

That's a real truck, on a real road, with a real driver. What else can I say. I guess the only way to know for sure is for you to test your own truck, with you driving, on your roadways.

believe what you want. it helps. it doesnt. its your truck.

bear this in mind though ive seen a lot of bent tailgates riding around most of them laying flat. makes me wonder how they got bent in the first place. personally i keep mine up and have no complaints.

for what its worth.

Honestly, I have been able to tell a difference with the tailgate down, when driving on the interstate. It seems to not have as much resistance. And with the rear glass opened there's not nearly as much wind blowing in. So I am assuming(hopefully correctly so), that I am getting better fuel effeciency that way(It may just be a mental thing though.).

The truck has the Mark III conversion kit on it so I am assuming it already has street tires on it. And since it is a conversion truck, I don't plan on driving it offroad much more than into the yard to move stuff whenever necessary.

Due to the nature of the job I am gong to be taking I have decided that I will be going with a the 15,000 mile synthetic oil from I believe Castrol. That way I will only have to change the oil once every two months minimum as opposed to every 10 days minimum, like I said before I am going to be driving up to 320 miles a day in the truck.

This one I picked up on VERY early into owning the truck. In fact I've gone as far as to traveling down the 55MPH highway instead of the 70MPH Interstate. Oddly enough my truck got the best improvement there. I went from getting 16MPG to almost 19MPG just by doing that. Not sure if having the tailgate down had anything to do with that though. I changed to a K&N Air filter but it does't seem to have helped much. Not as much as I had hoped, and not nearly as much as putting one in my Bonneville. I also switched to a Flowmaster Muffler, though that didn't seem to have any effect on the truck either.

Seems like the Dakota likes the 50 to 55MPH range the best, Although I like to drive 60 to 65MPH. Unfortunately on the Interstates around Middle Tennessee, if youre driving at least 75MPH, you're like to either get ran down, if not ran over, by a Semi, or come close to causing an accident, if you don't cause one.

One more thing I've noticed about that truck too, is that it seems to want to run a heavy mixture of gas -vs- air, which is why I bought the K&N filter. In fact until I bought the K&N, the truck would sputter out and quit once it got anywhere from 1/4 to 1/2 a tank. Now sometimes when I drive the truck it feels like the truck is running with some kind of limiter on it. I guess the only way I can describe is its as if the truck is driving uphill and having to drive at a lower gear to achieve the same speed, even though I may be on level ground or even a downhill. Is something possibly wrong with the transmission?

I just wanted to say Thank you to all for your quick responses about my truck. I will go looking into getting a lower difference ratio tomorrow.

They iignore it because they do not want public to know that is hurts MPG when they spend a fortune convincing them to pay P/U to replaces cars and that would hurt sales and profits and how do you sell a P/U without a tail gate? I agree that if you have a cover on bed that helps but with gate up and no covers there will be disrupted airflow and drag and the nature of that drag will change with speed and the faster you drive the worse it will be. AIr flows over cab and down in bed only to reach a barrier to be force back up again rather than straight out back of bed and this causes more drag with takes more fuel to overcome.

----------------- The SnoMan

These have got to be biased test because the shock wave created by gate up would vary a lot with speed and there might be a lower speed in which your senerio is played out but not accross the board and water test mean nothing as it acts differentlly than air to disruptions and not of these test factory in the hot expanded air traveling under truck and exhaust from truck too into slip stream. Plus these result can vary with small change in air density via tempature and altitude and even humidity can play a roll to. It simplyit do more efficent to drag a barrier wall through the wind than a mooth flow out of bed. If you beleive otherwise it is your right too if you want but it does not make it correct and being a pilot I really understand areodynamics and flow. Many years ago we had a test C141 that had a flat house for antennes attached to aircraft behind the rear cargo doors that was about 8 ft in diamet (rahter than the tapered tailcone A/C came with. It was found to effect speed and fuel consumption so much (even on a on a 150ton A/C) that when testing was over a specail tail cone faring was made to put on A/C when the rear mounting area was not being used for testing. You want airflow to colapse smoothly behide vehicle and not have to re-expand again to drag a flat tail gate wall through slipstream pushing air back up only to have it fall off again suddenly. This can cause a lot of drag.

----------------- The SnoMan

Before you do you need to figure out what you have now because if it fairly tall now in effective ratio, making it taller may huirt more than help.

----------------- The SnoMan

SnoMan wrote in news: snipped-for-privacy@4ax.com:

But there isn't any "they" acting in unison. Instead there are many pickup truck manufacturers in competition with each other. Each wants an advantage over the other. Don't you think that at least one truck maker has thought about this issue by now?

My understanding is that the air flows over the cab and by the time it comes back down it is long past the gate, hence the gate doesn't catch wind like a sail. This is also consistent with my childhood experiences of riding in the back of trucks. When you sit in the bed facing forward the air does not hit you square in the face as if you were riding a motorcycle.

Furthermore, if there were significant gains to be made by removing the gate or by installing a net gate, then practically every truck owner would have one by now. Pickups have been around for a long time. If removing the gate worked it would be widespread knowledge by now amoung truck owners.

Sit by the tail gate going down the road and feel the wind. Also "they" do not tell you that they use 93 octane in EPA tests or that they are hand built vehicle not random pulls and that the average speed for highway test is 48 and that Detriot tests the cars themselves not a independant lab. Do not be so nieve to think that there is not cooperation amoung competitors on some makers that is to all of their benifit

Maybe they would if they really new but then if they did they might not buy a P/U either so it is a catch 22.

----------------- The SnoMan

WRONG!! Try to follow this. When the air flows over the cab and into the bed with the gate up, a air cushon is formed, sorta like a cover, additional air flows across this cushon, makes the truck more aero.

Roy

Ever see an SSR? Not much of a pickup, but it's got a standard hard toneau.

Ever try to keep something lite and unteathered in the back of a p/u? The air in the box is FAR FROM still.