You can have my 2.47 differential......
 

....When you pry it from my cold dead fingers. :D
Thats the verdict after 1200 miles and 4 mountain ranges in 3 days. I'm throwing away my 3.07.

Can you provide some additional feedback on how often you would drive in third going upgrade?

Would you leave it in fourth, with full boost, or would you drop it down to third?

If you did drop it to third, would you reduce speed to 65 mph or so, or would you maintain the typical 70+?

All driveability issues are of interest.

Astroman, I sure like my 2.88 behind the 617 turbo and 240D automatic.

The only times (3 to be exact) I had to downshift into 3rd were when I got jammed up by traffic going up a hill and had to slow way down. Then I just stepped onto the kickdown solenoid and away we went. Nothing better than motoring past all the new japanese cars buzzing thier way up the mountain... :D
In short, it's very driveable, and yes, I prefer to let the turbo carry the car up hills, not 4k rpm..

My car will downshift into third at 75mph pretty easily with the 2.47. Plenty of acceleration, too. I really think the 2.47 is the way to go.

Jim

See? put your findings on the "easter egg post" as well. Pretty fun driving at that low RPM eh?

You can also have the same effect by installing larger tires. I ran the biggest tire that would fit in the wheel wells in my 83 300D. They were large enough that the speedo was significantly off (80mph speed with the speedo at 65). It drove very well though and did increase the fuel economy.

-Tad

The stock tire is 195/70/14.

I currently run 215/70/14's on the SD.

I might guess that you could possibly run (but possibly not) 235/70/14's.

The difference between this huge tire and stock is 9.3%.

When your speedometer reads 65mph, the vehicle is travelling 71 mph.

You cannot come anywhere near the effect of a 2.47 rear with a change in tires.

Thank you for running the numbers. I should have before I opened my mouth. I was happy with my tire change, and it is certainly an option for people.

-Tad

I don't see how tire width would change anything. Seems like going up to a 75 or a 15" would only achieve this.

remember that as the width increases, the aspect ratio for the sidewall (70% of the width of the tire in mm) stays the same, but the height increases.

What are your RPMs at say 65MPH
Also how can you tell the ratio from one that is installed on a car (ex. part number and location)

I don't know what you guys are talking about as far as noise goes.

Had my '83 300D at 85 on the highway and it was happy and not loud at all. Didn't even sound like it was straining.

How much of a top speed increase didja get?

Typically you can find a tag or stamped number code that identifies the ratio. Most tags are long gone after 20+ yrs., but then again, I don't know how MB axles are id'd. That said, you can manually check it by chocking both front wheels (back and front of each tire!), putting the car in neutral, and jacking up one back wheel. Rotate the back wheel once (be precise) and count the number of revolutions of the driveshaft. The drive shaft will rotate half as many times as the ratio, i.e. a 2.47 would rotate the driveshaft ~1 1/4 times, but a 3.07 would rotate it 1.5+. This works well discerning well-spaced ratios, but close ones can be tricky like telling a 3.54 from a 3.73. In this case, you make a "clock" out of cardboard (with a protractor) with a big hole in the middle for the driveshaft and a slit to slide it on. Then you mark the driveshaft and then you can see exactly where it stops.