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.