RE: Re: RE: M1009 Differential
Mileage isnt all about lower gear numbers (higher ratios). You need to keep in mind that your engine wants to run at an optimal RPM.
Take my 1009 for instance. I have stock 3.08 gears still, and the 700R4 transmission. At 65mph, I am running 1524 RPM. When I finally switch to 3.73 gears, I will be running 1839 RPM.
Now, the optimal Torque/HP combo in the 6.2 engine occurs in the 1800-1900 RPM range. This is where your ideal engine conditions are, such that if it were setup for constant speed for a pump or something of that type of use, it would be set to run at that RPM. This is where you will get the best mileage under a 'load'.
I do agree, that it is possible under certain conditions, that the 1500 RPM might produce a better mileage (nice flat expressway), but how many of us routinely drive just that?
Now lets talk in terms of the stock tranny, since thats what most 1009 owners have.
With the stock 3.08 gears, at 65mph, you are turning roughly 2300 RPM. With 3.73's it will be 2776. In order to match the final drive ratio of the overdrive tranny even with the 3.73's you would have to go down to a 2.59.
I had set out writing this with the intention of proving a gear change is warrented in the 1009. What it seems I have done, is really a tranny change is needed followed by a gear change (incidentally, I was already headed on this path). The problem with just 3.08 gears and the stock tranny, is you dont have enough gears in the transmission to have the 'power' you want for every day driving.
For a great site for running all these #'s go to
http://www.grimmjeeper.com/gears.html
They dont list the 3.08 gears, but for all practical purposes the 3.09 is the same. The 1009 has a TH400 transmission stock, and the overdrive I have installed is the TH700R4. The transfer case is a NP208.
Glad to answer any more questions...