DID I GET THE SHAFT? / I think I was sent the wrong differential.
 

The differential I ordered was to be a 2.66 ratio from an 85 SD

This is looking like a 3.11 from a 123 / Is this correct?

http://www.greasemachine.com/benz/Picture%20054.jpg

http://www.greasemachine.com/benz/Picture%20056.jpg

Looks like a W123 alright. I don't think there is a 3.11
The ratio is stamped on the face where the cover is attached, lower left corner.

THANKS
2.88 it is!!

Good! you got an '85 diff.
Now, something bothers me. Why a 123 case number? For a 126 car, right?
MB does use some 123 parts, even 115 parts in 126 cars, its not unheard of, for economic reasons, why make a special part for every darned thing in the car, right? I just don't have a 126 handy to check. If I can I'll stop at a friends shop and see if there is on on the lift.

You should check to be certain the width of the existing diff case, measured at the faces where the axles go in and rest, and compare to the differential you bought. You need a long dial caliper set up on a machinists magnetic base, I frankly don't know how I'd measure that. Checking MB specs would be easier maybe someone can do that for you.

If there is a slight difference in this dimension you may need the spacer rings that fit the axle shafts where the splines go into the casing. These shim rings (one at each end) are precision ground to a specific thickness depending on the application and determine the slop that exists between the axles and the housing. They should just allow just enough freedom to move the axles in and out and the clips will go on with a little effort. OTOH if there are 20 - 30 mils (.020 in) slop it's excessive and you need thicker shims O/W you will have a thump when first accelerating or worse yet the clips may come off :eek:
MB used to sell the shim rings in a kit buts its an expensive kit and may not be available. I llike to get the shim rings when I purchase the differential as the items are removed from the donor car.

I seem to remember putting different shims in a 126 diff when installed in a 123 car, you are going the reverse way around so that is why I mention this. Hopefully it will just go in and you'll not have any problems. Let us know.
It should make for a nice ride! My '83 300D is much better off with the 2.88 in her. What a touring car!!! :D :D

I was told it came off a 126 but it will be installed on a 123 so it is exactly what I wanted!