Now that I have put a few thousand miles on the 2.47:1, I can say that it is a little bit high for the average 617 and other folks who have suggested a 2.88:1 seem to be spot on, IMHO anyways.

While we did not net the 4-5 mpg increase in mileage we had hoped for (during this experiment) we were able to maintain our average fuel economy of 25-28 mpg (and sometimes 30 mpg but not consistently) while increasing the cruise speed from 55-60 to 75-80 mph.

Over the past 20 tankfuls, mileage numbers have been consistent, with calculations altered for the 7.29% speedometer error.

It's a great gear on the highway.

I've recently driven from California to Texas a couple of times and drove the W116 for test purposes and trunk space. On the first leg of that trip I drove non-stop 75-85 (where I could do so safely) with the A/C on and got a full 610 miles on 19.5 gallons, for about 31.2 mpg.

The hills do slow the car down, but it will climb the 'Grapevine' in 4th gear at 70 mph at a little bit off the kickdown switch and I have never had to kick it down into 3rd.

Driving up into Big Bear, California is another story. There are sections where the grade is as steep as 16% in some sections and climbs several thousand feet. That climb involves a lot of downshifts and WOT.

It's a great highway gear to be certain, but as other have posted, I think the 2.88:1 is about as far as one should go.

Hope this helps...

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Now this is amazing to me. Even our Volvo S70 and Volvo XC70 Cross Country continuously hunt between 5th and 4th gear on the Grapevine when maintaining 70-75 mph.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Keep in mind the old 722.120 transmission requires you to depress the kickdown switch for full throttle. Your cars are computer controlled I believe and the ECM probably tries to keep you in an optimum rpm band.

It will normally downshift from 3rd to 4th at about 30 mph...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership