Diff swap, what do I need to know?
 

I am building up a 1983 300SD, performance injection pump, intercooling, different turbo etc. I want a highway runner that I can get some mpg out of, like 2000rpm at 70mph instead of 3000 range. What diffs fit back there and what ratios exist, I need to pull the rear axle shafts anyways for boots etc I would like to swap the diff too. I plan on building the car so it has power at lower rpm, my direct injection VW's and smart make me want to...and would like to get better economy out of the benz, it is hard to drive it when all the other cars get two or three time the mpg...

2.24/2.47/2.88 (you have 3.07 now). Only 85 and before diffs work. The 2.88 is in the '85 300d/300sd, the 2.46 is in the gasser W126s, the 2.24 is in the W126 coupe.

You're only looking at a couple mpg increase btw. Also, drive slower, it's not just rpms but air resistance too.

The 224 is I believe only from the euro 500 gassers. The us spec 500s run the 247 diff. If you can find a 224 good chance it is a limited slip.

There is a EURO 500SEC at our PNP, checked out the Diff, and it is 2:24.
and as of yesterday still had the Euro bumpers and white lights in the front bumper.

Charlie

Thanks for the info, is the ratio stamped right on the diffs? I am looking at changing were the power band of the engine, and want to lower the highway rpms to suit it thats all, I drive a Smart CDI when I want fuel economy!

The Gear ratio is stamped on the lower left facing the rear.
just scrape off the grease.

Charlie

2.24 on a SD is going to make it sloooow off the line. Its ok with a 2.47 and an '85 torque converter (2400rpm stall speed).....I highly doubt you'll see much more than a 2-3 mpg increase with all that work. My dad's 300SD now has a 2.47....and it gets maybe .5 mpg better than before....but its a lot quieter.

Put some taller wheels on it.

Charlie

Yes taller rear wheels is the way to go cheaply.

With a Diff swap, make sure you have the axle shims. Those shims are part of the diff, not the axle, even though they are mounted on the axle.

Those shims are unique to both parts, axle and diff.