125 k is about 78 mph, so yup I guess i like to drive 80. ( I'm a pretty safe driver, but the roads here really aren't very crowded)

At 70 mph the tach reads 3200rpm. I'd like to aim for 3000 rpm @80mph.
Is there a common MB wheel and good tire that will fit the '83 300cd I have, to achieve this?
thanx Alberta Luthier

You cannot achieve 3000 @ 80 mph unless you switch to a 2.47...................

I think that this thread addresses the 123/126 differential interchangeability.

http://www.peachparts.com/shopforum/showthread.php?t=153435&highlight=2.47

Good Luck,
Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S

Yep, I forgot about him. Clearly the diffs are interchangeble. The W126 diffs do fit the W123........just be sure that the W126 is 1985 or before.

Thanks for the info.

reads this title... Nah! not likely!
Thank you all for such a good response to my questions.

rudolphgreen’s thread ‘holy 2.47 sleeper’ was informative but left me thirsting for the 2.47 In that thread, reiner and t walgamuth were saying a 247 came out of a 380

B.C. ‘The W126 diffs do fit the W123........just be sure that the W126 is 1985 or before.’

So If I have this right…. I can use a 2.47diff from a:
1980-85 W126 (does that mean an.SD? SDL? Or other models too?
1980-85 380?...gasser?
Or perhaps a 2.88 from a 1985 300D?
Have I got that part right? And are there any other years models for a 2.47 or 2.88 diff that will be easy for me to get the required parts from, and bolt up to my 83 300CD? Sorry if I seem a little dense, as I am newly afflicted I haven’t yet learned all the models.(and now while the wife is out of town I find myself studying models rear ends???)
Thank you all for your patience and assistance.

The 2.47 will be found on the gassers from '81-'85. I believe that any of them will do.

You can't use the diff from any of the diesels from '81-'84 because they will have a 3.07.

You could use the diff from the '85, which is a 2.88, but it appears that you'll prefer the 2.47 if you routinely go 80 mph.

I'll be curious to hear how drivable it is with a 2.47. I spend hours at 80 mph at 3500 rpm with my 3.07 and 205 tires. Lower rpm would be nice, but not at the expense of insufficient power to cruise up hills at highway speed. Personally, I don't think I would try to go any higher than 2.88 unless I had some info from someone who has done it first.

If you're in Colorado, I would say the 2.47 would be unbearable.

Here in the flatlands of Chicago, the 2.47 is manageable because the land is flat. My wife and I drove out to western Illinois yesterday, and when going up hill from a river valley on I-80 @ 65mph, the engine was a near maximum fueling (can't say full throttle) to maintain that speed. That was with the AC off; with it on I was loosing speed.

In July we are driving east to Virginia; I'll report back how well it crosses the Appalachin Mountains.

Thanks, that's what I was afraid of. I would like to have lower rpm, but I don't want to end up with 240D-like performance on the highway. What these things really need is an overdrive.

I agree. The 2.88 is taxed on a decent grade (estimated at 4% or so). The SD can barely hold 65 mph on that hill. The 2.47 would require a downshift and the use of 3800 rpm to hold 70 mph in third. Even more moderate grades will have you mashing the pedal in anticipation.

The 2.47 is great for flatlands.........but........that's about it.

I would actually prefer a 5 speed manual. The non-locking torque converter doesn't help economy either.

My sentiments are the same as Brian's ie the 2.88 is the right gear set unless your driving across like Kansas all the time.
And the car should be a good running one too, with an ALDA tweak to get off the initial starting line, valves lashed properly and good injectors, etc.

I'm running a 2.88 in my '83 300Dt and its great! I highly recommend going to a 2.88 in most cases. But, if I had to haul a bunch of people up hill a lot (around here we have some fairly steep hills) I'd probably have kept the 3.07

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I'm an hour east of the rockys, mostly flatish with a few low hills, then quite flat east from here. While I find 80 mph very comfortable I don't want to over gear it. I've been thinking that as I learn to tune/tweek the engine I'd get a few more usable horses and I'd like them to have long legs. Maybe I ought to reconsider the 2.88 and go higher profile wheels/tires later, if it seems to still have the potential to turn them.

Are there other models/years besides the 85 sd.sdl., that have a suitable 2.88? I'm hoping to locate one on this side of our border because shipping etc.

The 85 300D also has a 2.88, I'm not sure what else does.:

http://www.adsitco.com/category.asp?CID=416

http://www.adsitco.com/category.asp?CID=418

BTW, this is not a recommendation for Adsitco, just some reference info.

1985 300D
1985 300SD

That's it.