380 diff in 300cd? - PeachParts Mercedes-Benz Forum

Alberta Luthier · #1 05-29-2006, 09:57 PM

I'm considering buying an 86 380 diff. , Seller says 180k.
Will it fit my 83 300CD? Is it a BIGGIE to change? I've done quite a bit of mechanical work on various gas guzzlers years ago but I am a Newbie to MBs, anything I should know about it? What is it worth?
I appreciate your opinions.
Alberta Luthier

Hit Man X · #2 05-29-2006, 10:05 PM

'86+ have different mounting flanges... so they will not work for sure. I'm not sure if early W126 diffs will fit the W123s or not.

Brian Carlton · #3 05-29-2006, 10:11 PM

Agreed.

The diff from the '86 will not fit earlier vehicles.

Alberta Luthier · #4 05-29-2006, 10:26 PM

Ohhhh you guys are GOOD! I've been buying a lot of small expensive parts for my new ride and I REEEALLY am glad I didn't buy & ship a diff that won't work.

What I need I suppose is a list of years and models that will work in my '83 300CD and have the holy 2.47 ratio that I yearn for!
I have searched and found a few bits and pieces but clearly was/am confused.

Brian Carlton · #5 05-29-2006, 10:31 PM

Quote:

Originally Posted by Alberta Luthier

Ohhhh you guys are GOOD! I've been buying a lot of small expensive parts for my new ride and I REEEALLY am glad I didn't buy & ship a diff that won't work.

What I need I suppose is a list of years and models that will work in my '83 300CD and have the holy 2.47 ratio that I yearn for!
I have searched and found a few bits and pieces but clearly was/am confused.

I'm not sure if we have confirmation that the diffs from the W126 fit the W123. If they do, then you can get a diff from any V8 from '81-'85.

The W123 never had a 2.47 ratio installed and, I don't believe anyone on the forum has put one in the vehicle.

Alberta Luthier · #6 05-29-2006, 11:01 PM

Quote:

Originally Posted by Brian Carlton

I'm not sure if we have confirmation that the diffs from the W126 fit the W123. If they do, then you can get a diff from any V8 from '81-'85.
The W123 never had a 2.47 ratio installed and, I don't believe anyone on the forum has put one in the vehicle.

I have some gas engine experiance but I would rather not be the guy who first attepts this

In an effort to make my question pointed I have overstepped my knowledge, a classic Newbie error I suppose....
What I should ask is: 'what do you reccomend?'
I love my new ride, but the engine is turning over faster than I would preferr at 125 km (maybe 85mph?)
It seams to have more than enough power to pull taller gears. (the roads here are not very congested)
Should I change to larger diameter wheels/tires?
Any thoughts?

Brian Carlton · #7 05-29-2006, 11:11 PM

Quote:

Originally Posted by Alberta Luthier

What I should ask is: 'what do you reccomend?'

Should I change to larger diameter wheels/tires?
Any thoughts?

Well, I suffered from the same malady and I found and installed a 2.88 axle from an '85 SD. Together with 215-70-14's, the engine rpm's are now down about 10% from stock. The engine turns just under 3K at 70 mph. It's quite happy at this speed.

However, if you routinely run 80 mph, then the 2.47 is preferable. The W126 diff is common with the W123 provided that the year is prior to 1986.

You can definitely get a 2.88 if you can find a '85 300D or an '85 300SD

TheDon · #8 05-29-2006, 11:12 PM

Quote:

Originally Posted by Brian Carlton

You can definitely get a 2.88 if you can find a '85 W123.

its got to be a gasser w123 right

Hit Man X · #9 05-29-2006, 11:13 PM

That's what I believe also as the early W126s had a smaller ring gear too (180mm I recall reading on here).

Hit Man X · #10 05-29-2006, 11:13 PM

Quote:

Originally Posted by TheDon

its got to be a gasser w123 right

Those are geared deeper. The 280E I almost bought had a 3.49:1 I think!

TheDon · #11 05-29-2006, 11:16 PM

Quote:

Originally Posted by Hit Man X

Those are geared deeper. The 280E I almost bought had a 3.49:1 I think!

so an 85 w123 diesel.. which i have .. i thought 3k rpms at 70 mph was pretty high for this car.. i was thinking 2400 rpms would be a sweet spot at 70

Brian Carlton · #12 05-29-2006, 11:27 PM

Quote:

Originally Posted by TheDon

its got to be a gasser w123 right

The diesel W123's had the 2.88 in '85.

The gassers (V8's) had taller axles.

#13 05-29-2006, 11:38 PM

Quote:

Originally Posted by TheDon

so an 85 w123 diesel.. which i have .. i thought 3k rpms at 70 mph was pretty high for this car.. i was thinking 2400 rpms would be a sweet spot at 70

That would require something like a 2.4:1 ratio. I've never heard of one that high in a 617. I suspect it would be too high for driving around town (you would always be in 3'd) and you would probably run out of power long before you ran out of rpm at high speeds.

The cheapest (partial) solution is to run 205 tires, which only gives you about 4% higher ratio than stock. You can feel the difference pulling away from a stop, but its not too bad, and you run about 100-150 rpm lower at highway speeds.

t walgamuth · #14 05-29-2006, 11:39 PM

i believe the 123 280e carried a 354 from the factory. the 115 280 carried a 369. i suspect maybe the 369 was used with the less powerful carbed cars.

tom w

Brian Carlton · #15 05-29-2006, 11:53 PM

Quote:

Originally Posted by TheDon

so an 85 w123 diesel.. which i have .. i thought 3k rpms at 70 mph was pretty high for this car.. i was thinking 2400 rpms would be a sweet spot at 70

Actually 2800 rpm is the sweet spot, IMHO. Your are right there at 70 mph with some larger tires.

The 617 doesn't start to complain until you get above 3K. Now, if you routinely travel at 80 mph, that's another discussion.