I remind you that I disagree with the attempt to lower the revs on the SDL.

It starts to finally run well at 3000 rpm and above. Why do you want to burden it with higher exhaust temperatures and lower rpm's? It makes perfect sense for the five cylinder engine that likes to run at 2400-3000 rpm, but, this engine likes to run at 2900-4000 rpm's and it's quite happy to do that.

I drive in the city quite a bit and would rather not spin ~2600rpm at 45mph when I could do maybe 2100-2300rpm with the 2.47:1

I do agree it feels fine at higher RPM over the 617, but I'm curious how it'd do with the taller axle. Worst case, I'll swap it back to the 2.88:1

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

is smoother and sounds and feels fine running higher rpm, i think it will still benefit in fuel economy and longivity by running a lower rpm.

the 560 sel rear end may have posi on at least some of them. i am not sure why i think this. my mb buyers guide doesnt mention it.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

.........ahh.......that's why you have 4th gear........you'll be turning 1900 rpm

Ah, touché

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

And, if anyone needs one, I have a 420SEL diff (2.47 late style) which I thought I could put in my 300SD but as it turns out... nope. PM me!

I wonder if you could swap those gears from the 2.47 into your housing? Setting up gears is not that hard especially on a housing on your work bench.

It might work, but the 2.47 gears are physically larger (185mm vs 205mm?) and the 2.47 case is physically larger.

What yrs./models are these in? I am thinking of putting one in my 83 300D. I know it will be sluggish, but 90 % of my driving is flat highway so I want the fuel economy.

Any modifications needed for it to fit?

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81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

i think brian mentioned the years about 8 posts back.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I don't believe there were any W123 cars that used 2.47 differentials. I also do not think you can use the W126 differential in a W123.

How much of an increase in your mileage are you expecting to see? If you think you are going to see consistent 30's then save your pennies.

Please reference my mileage chart at www.pokrefke.com/benz/benzmileage.htm (Note: the diff was changed from a 3.07 to 2.47 in February 2006)

Using the stock 3.07:1 differential I drove 12,209 miles and used 468.7 gallons of fuel for an average fuel economy of 26.04865 mpg.

Using the 2.47:1 differential I drove 11,791 miles and used 426.9 gallons of fuel for an average fuel economy of 27.62005 mpg.

The economy increased 5.69% or 1.571406 mpg using the 2.47 differential.

Although the engine does turn slower and makes for a much more quiet car, you are just not going to see a huge gain in economy.

are you cruising the same speed?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hmmmm...........20% reduction in rpm's............5.7% improvement in economy.


........sorry.........couldn't resist........

Are you two still having that "discussion"?

Tom,
Aye, still the same speed.

Not sure what the discussion is about, I just didn't want someone to make the swap thinking they were going to get vastly improved fuel mileage.