I have a 1981 240D manual transmission that I love but have been very frustrated by running out of gears at 25mph .(shifting from 3rd to 4th). And at 70mph on the freeway it's downright frightening!!!
So I swapped in a 2.88 rear end, replacing the 3.69. The 2.88 rear end is a one year only, 1985 300D, TD, CD, but not the SD.
I've read this would make the car an even bigger slug than it is but, quite the contrary, it even seems to have better acceleration. Also now, I can shift from 3rd to 4th at about 48mph and freeway speeds are much, much more quiet. A word of caution, if you go looking for a 2.88 from a parts car, get the Speedo from that car as well as the gearing in the Speedo is matched to the differential.
Buy the way I also have another 240D that has the OM617, 5 speed conversion that I did the same swap on and now at 70mph I'm cruising at 2200 rpm's.

Could swear the 85 SD's had the 2.88 also. Another one year only, because 85 was the last year of the Gen I

You are correct, my 1985 SD has the 2.88:1 from the factory also. The OP is incorrect.

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What size tyres have you got?

I'm surprised that a little 240D is able to cope with a 2.88 rear end any where except flat little Holland (with no wind!).

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1992 W201 190E 1.8 171,000 km - Daily driver
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Don't leave that there - I'll take it to bits!

IIs there any time you have difficulty getting underway from a stop? Some 240d engines seem to have a little more power than others. I attribute this to several things but still it is what it is.

Also did you notice any difference in fuel consumption? Base oil consumption? I wonder at what rpms peak torque is present. Car still does okay on hills if you drop a gear? You may be the first to attempt this. I did not think the 240ds could cope with this other than perhaps the automatic versions..

Keep in mind that these little engines have really nice torque so no problem what so ever from a standing start, I actually feel like its faster. Before 1st was a throw away gear, basically you came out at 5 or 10mph, now you can stay in it up to 20mph. I'm using standard wheels and tires. It's a completely different animal from before and I couldn't be more pleased. Mercedes just had it geared way too low.
No fuel consumption data yet but expect a nice bump up.
The 85 SD is a w126 and this chart shows it's probably not compatible:

differentials, gear-ratios and compatibility | Mercedes-Benz turbo

Actually, 1st-gen W126 1.1L rear ends fit into the W123.

The 300SD 81 - 84 3:07 and 85 2:88 Diff will fit in a w123. The spedo`s will not.
They are electric. The w1123 are mechanical. And the shape is different.

I have an 80 240D as a DD, and do not see how you get to 4th gear at 25mph.
When I drop to 40 mph I grab 3rd gear to keep the eng at a proper RPM range w/o lugging.

I swapped in a 3:58 Diff from a 280E so I could have the 150mph spedo.
That small of difference did not make any difference from a start.
But going to a 2:88, I would say you are on the edge of lugging the engine and slipping some on the clutch.
We are talking about 67 HP here.

I swapped in a 4-spd in our 85 300D, and it has the 2:88 Differential. For the most part it is ok.
But try starting on a steep hill, and you are going to be reving the engine and working the clutch just to get her going. Most highway grades are ok, but I was on a friends
very steep driveway. I needed a couple gears lower than 1s gear.

There is a guy with a 240D some place in Kansas that installed a 3:07 in his 240D, and has good luck with it.
But Kansas is pretty flat.



Charlie


sent from my pos computer

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I don't agree that Mercedes had it geared way to low. I think it probably just needed the the 5th gear that you could get in Europe.

I'm also having a hard time wrapping my head around crawling around at 25 in 4th. With mine I'm flat to the floor in 3rd before I get around to shifting up to 4th at around 40 to 45 depending on traffic conditions.

- Peter.

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1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
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1984 123 200
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1972 Cadillac Sedan DeVille
1971 108 280S

Exactly. 4th is of no use below 40mph in a 240D. At 25 in 4th some SERIOUS lugging would be going on and that's very bad for the engine.

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Most of the "5th geared" vehicles have a lower geared differential to remove the benefit!

I think on the whole the W123 was built for a different time where road speeds were slower.

If in the US of A the old fashioned 55mph maximum was forcibly regulated the gearing wouldn't seem too slow!

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Guys, keep in mind LA is FLAT and easy weather...

The 240 has very little weight, so, as long as stock or smaller tires are used this would work... Clutch wear is going to be much increased. ..

Yes, the 85 SD also has the 2.88

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You were in 4th gear at 25mph? You were shifting WAYYYYYYYYYYY too early. You're right, 1st barely gets you moving, 5 mph perhaps.

My 190D shifts like this:

1st to 5 mph
2nd to 20 mph
3rd to 40 mph
4th to 60 mph
5th to 80 mph

That's how I shift normally. 1st and 2nd I usually shift at 2500 rpm. 3rd and up I'll shift at 3000.

If you were in 4th at 25 mph that engine was lugging.

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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
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Way, way different from a 240D, 4sp

This is the part that makes no sense to me, and, I think, robs some of your credibility. I can't see how a switch from the 3.69 to the 2.88 would make the car peppier.

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