Rear Diff Question
 

Can a W124 rear diff with a 2:65 ratio fit and be used on a 1985 W123 with a 617-952, that originally has a 2:88? If it does, is it a drop-in fit without modifications and spacers?....and if not what are the necessary modifications needed to make it fit and work?

No, its completely different.

What about a rear diff out of a W126? Let's say a 2:47.....too tall for a 617..? Are there any W126 ratio that is somewhere in between 2:47 and 2:88?

You may be able to use the rear diff from a w116 450se/sel. That's a 2.65. The 617.952 can push a 2.47 gear, you will need to downshift manually if you need to pass or climb a grade.

there is an early 126 247 that will fit without major surgery. Yes with an automatic you can run a 247 rear with a 617. I don't know if you can get a working speedo in the correct calibration though.

Has anybody tried a rear diff transplant into a taller ratio into a W123 with a turbo 617? Any ideas on what are the engine speed gonna be on a 2:65 and a 2:47 respectively when cruising at 70mph on a flat level road?

Several folks have done the 617 247 swap with success.

Myself, I have a 123 with a 300d na euro motor running a 307 diff and the five speed overdrive which about equals a 247 final drive ratio. Its very fine on the highway and the only real drawback is getting it going, especially if starting off on a steep hill.

And I have gotten as high as 36 mpg highway with it.

Tom W

2.47
 

I have a 2.47 in my 83CD and it's great. 1st gear is usable now and 3rd is good for getting out there starting a pass. It's an automatic so slips what? maybe 5-600 rpm. A 2.47 would be way tall with a manual tranny though. However I think I would like a manual trany and a 2.88.

Also for all sorts of mechanical (and it seems sometimes like magical) reasons some of these motors just make a little more or less power??? My CD was a very peppy car with the 3.07 and it really (seat-of-pants) doesn't feel much slower with the 2.47. My 84 SD runs pretty good but never has had the power the CD does, if I ever get running as well as the CD I will start looking for another 2.47 diff for it.

I have a 4-speed and the 2.88. The pickup from a stop is nice, and it's fits perfectly for starting up a hill, but sits just below 3K rpm at 70mph. I am looking for a 2.47 right now because I am going to be doing a good bit of hwy driving in the coming year. I know it's going to be a really slow start, but I need to give it a try.

I will find that very interesting, please let us know how that works out. I would very much like to have a manual and a 2.47 but am afraid the engine won't be able to pull the car into the best power band in high gear... but maybe with a manually controlled vnt turbo (or a smaller turbo that spools up at lower rpms)and a modified I.P.??

I would like to install an intercooler and a vnt, but I have bigger fish to fry at the moment. From my calcs, I should be at about 2430ish rpm at 70mph. That is right around the max torque range.

I might try to put a 2:65 out of a gasser W116 then, if I come across one of 'om and see how it does.....a 2:47 would be great but, it's a bit hilly here in 'Bama.....

reason I want to convert is that I need a newer one since my 2:88 is sort of making clunks already, especially at full stop from P to R and from R, N to D... so instead of putting another 2:88, why not try a taller geared diff......

Thanks for all the replies Gentlemen!!!

I am thinking about that too. I'll probably take whatever I can find first.

Don't forget about speedo correction.

I was just thinking about that on my drive home from work today. How interchangable are the speedos from those cars to a w123? If they don't interchange, I wonder if some of the internal gears could be swapped to fix the ratio.

That would fix the odometer but the speedometer uses a magnetic barrel to drive the speedo needle.

swap the gear out of the tail housing on the transmissions.

That's not how the speedos are calibrated in these cars.

The transmission drive is identical in all of MB's models. What changes is the speedometer calibration based on the differential ratio.

So you probably want to get the speedo out of the car you get the diff from. Or if you are feeling very generous drive around with your speedo way off and sell the speedo to me (if it came out of a car with a 2.47, it was already gone out of the car my diff came out of)

Unfortunately the speedo on a w126 2.47 ratio is electronic and will not work on a w123 except the 1981 TD.

Then swap the tailhousing from a W126 300SD.

I could easily be wrong but I think they went electronic in about 85 (when they also changed the diff mounts) and the ones before (I don't know how long before) were interchangeable.

anybody have any idea what w116 years we are talking? put close to 10k on the 2.47 and it is outstanding..
but it has been just a little bit tall, and need to be watching the speed.:D the xcntry cruise was exceptional though.:thumbsup:

Not sure on the years, but here is a reference list of potential diffs found in this thread

R107
---------
380SL,SLC RATIO 1:2.47

380SL,SLC,560SL RATIO 1:2.47 ABS

450SL,SLC RATIO 1:2.65

450SL,SLC RATIO 1:3.06

W116
----------
280S,SE RATIO 1:3.69

300SD RATIO 1:3.07

450SE.SEL RATIO 1:3.06

450SE.SEL RATIO 1:2.65

W123
----------
230,240D RATIO 1:3.69

280E RATIO 1:3.58

300D RATIO 1:3.46

300DT 85 RATIO 1:2.88

300DT TO 84 RATIO 1:3.07

W126
----------
300SD 85 RATIO 1:2.88 ABS

300SD TO 85 RATIO 1:3.07

300SDL RATIO 1:2.88 ABS

300SE,SEL RATIO 1:3.46

380,500 RATIO 1:2.47

380,500,560SEL RATIO 1:2.47 ABS

420SEL RATIO 1:2.47

W124
----------
260E RATIO 1:3.27

300D 1987 RATIO 1:2.65

300E RATIO 1:3.07



Side Note.. I believe the 2.65 is a LSD, 2.47 off a 420SEL and 560SEL is a LSD and 3.27 from some W124 are LSDs.

Correct me if I'm wrong, but everything on the list except for the w126 and the w124 will work on the w123 right?

My understanding is w116, early r107s, and first generation w126 (diesels versions are direct plug in and play) would mount up to the w123, but may require change of flange to accommodate the w123 flex disk and has to be mounted with a slight tilt to get a proper angle for the driveshaft. . All W124 and later generation w126 will not work because of different mounting.

True to some extent, but actually all w126 are electronic. All w123s are most likely cable driven except the '81 TD and all w116 is cable driven.

Anybody else have any more info on this (specifically to the w116 2.65)?:bulb: