I changed the 3.07 differential in my 300SD with a 2.47 from a 1982 380SE. All told, it took me about 6 hours, start to finish. Even with snow falling, it wasn't that bad of a job.

Here are some parts/tools you will need if you undertake this project:

+ 30mm, 12 point deep socket to remove the drive shaft yoke on the diff. I bought one from SnapOn for about $40 (I bought the impact socket, non-impact sockets are cheaper.)

+ 12mm, 1.50 pitch lock nuts (qty 4), for the differential mounting studs.

+ this is a great time to replace the flex disc and the pinion bearing seal.

+ a floor jack with a tall reach. I bought the 2 ton aluminum floor jack from Costco for $100 and it worked well.

Here's a tip - put the clips on the axle shafts BEFORE you bolt the diff in place. I needed a thinner spacing washer, and had to remove all bolts and drop the diff to swap the washers.

Unfortunately, I don't drive the 300SD during the salt season in Chicago, so I will have a couple months before I can give a drive report. I track the mileage of each tank of gas, so I will be able to report any mileage improvements.

Sounds nice, since my SDLs suspension is in worse shape than the SD... I plan to install a 2.47:1 in there first.

__________________
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]

When my rear boots fail at some point in the future I am going to get new cv axles, and put in a 2.47 if I can find one....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Took it on the tollway this morning and recorded the following rpm/speeds:

60mph = 2150 rpm (estimated)
65mph = 2450 rpm (estimated)
70mph = 2600 rpm (estimated)

0 - 60 increased by 2 seconds (11 seconds with 3.07, 13 seconds with 2.47), but it does not feel significantly longer in my opinion.

The car just cruises down the road quite leisurely. On my 1600 mile trip in November, the car was turning 3200 rpm @ 70 and was quite loud.

I'll be interested to see if the lower rpm requires a higher pedal settling which would offset any mileage increases. We have to wait until Spring for that.

Nearly a 400rpm drop at 70mph for me as I have 2.88:1s, I like those RPMs a good deal.

__________________
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]

I'll keep my 2.88's also. Nothing like cruising around 75mph and you are right in the sweet spot.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

What did you do to your Speedo to match it up to the 2.47? whole new speedo? Or did you have your existing one recalibrated?

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The 160mph speedo out of a gasser 126 is a direct replacement, already calibrated for the 2.47 gears. I verified the accuracy with my GPS unit, and it was off .2 mph @ 70.

I found a couple of boxes to recalibrate the speedo if you are interested in keeping your original speedor, but the boxes cost ~$100 and I paid $30 for the entire cluster from a 380SE.

what ratio differenital will my 1985 cali 300D have. i think i saw in an earlier thread that it was somehow special. anyone know?

if i have a 3.07 then i would love to go to a 2.47.

__________________

Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

Your 85 should have a 2.88 stock ratio.

I am looking at doing this swap as well into my '84 SD. Will a 2.47 from ANY W126 chassis work? Are there any mods that have to be done to the new diff to make it work in an SD?

Thanks
Brian

When I do the swap I want to find one from a 560SEL that has the limited slip inside it. That'd help a lot in off-the-line in snow around here.....generally what happens is my right tire spins out, while the left just sits there, if the left did something too, I'd save on tires and actually get going faster....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

More specifically, will a diff from a 560SEC work in my SD?

Bravo,

What year is it from? If it has the 4 mounting studs, it should work fine. Don't forget that you will need to swap the driveshaft yoke (the gasser flex discs have a larger bolt hole diameter).

Thorsen,

It is from an '86 SEC...