2.88 differential fuel mileage questions
 

What is to be expected in terms of improved fuel mileage if I were to switch from a 3.07 to 2.88?? Say cruising about 65-70mph?? How about in-city fuel mileage??

- Thank You.

Probably barely anything.

Ask someone who has experience with both an 81-84 SD and an 85 SD. Or is it only California SDs with a 2.88?

Sixto
87 300D

Several years ago, I swapped the slightly noisy 3.07 in my '84 300D for a good 2.88.

No real difference in economy (maybe a 1/2 mpg at best...I never could get solid economy info out of that car) but it did drop the revs at 65mph to 2750ish.

I have a 2:88 in the 85 with a 4-spd manual, and you will pick up 3 mpg.

I have never driven the 3:07 to compaire, but there is about a 6.7% difference.

85`s all had the 2:88 Diff. 300D and 300SD. If you do swap in the Diff, grab the Spedo also. they are geared together.

Charlie

charlie, do you see these 2.88 pairs from time to time during your travels? i might take one off your hands if you could find it.

I have monkeyed around changing diffs on quite a few vehicles. I expect on a diesel to improve equal to the mechanical difference. As charlie says it is slightly less than 7%. 7% would give about 2 mph more economy.

Changing from an auto to stick gave us a bit more than that in my 300 cd. It went from about 25 highway to nearly 30.

IIRC my '84 300D has the standard 3.47 diffy, and I'm considering the same swap to a 2.88. Is that worth the effort?

From the threads I've read on the subject it looks like my rpm at 65-70 mph would drop from 3,000 to about 2,500.

Same threads don't really discuss mpg... just that the rpm drop puts the 0M617 squarely into it's power band. What kind of mpg increase might I see with the 2.88?

Your vehicle has a 3.07 diff. Switching to the 2.88 lowers the rpms slightly and provides less noise at 65 mph.

Did all 123's move to the 2.88 gears in 85? My 85 TD seems to rev awfully high and I am wondering if the 2.88 only went in the sedans.

What's the rpm at 65 mph?

The 3.07 is right at or just above 3000.......depending on tires.

The 2.88 is at 2800 or just above.

"Awfully high" is relative.

I'll double check next time I drive, but I am pretty sure it is above 3000. I usually run about 70 and the tach hangs out around 3200. It runs 2500 at 55.

Pretty sure 2,88's were installed across the line in 85 since I have an '85 TD with 2.88s in it.

Read this thread. The mileage question is covered pretty well even if there are drastic differences in member's results.

I have both in 123 chassis (3.07 in the 82, 2.88 in the 85).

as others have said, 2.88 cruises at about 65 mph @ 2800 rpm, 3.07 is about 3200 for 65 mph.

its a difference mostly in noise. maybe 2-3 mpg difference, but its barely noticeable.

as having both, i personally wouldn't seek to swap to a 2.88 from a 3.07 unless there was something wrong with the diff and it had to be swapped anyways.

I see them from time to time, there were 2 a SD and a D in 2 different yards about a month ago. where are you located? they are heavy so don`t know what shipping would be.


SIRNIK84 put one in his 84 300SD when he did the 4-spd swap, said it really improved his performance, is really happy with it.

Charlie