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  #1  
Old 09-26-2008, 09:08 PM
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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?

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  #2  
Old 09-26-2008, 09:11 PM
ForcedInduction
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No, its completely different.
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  #3  
Old 09-26-2008, 09:14 PM
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Quote:
Originally Posted by ForcedInduction View Post
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?
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  #4  
Old 09-26-2008, 09:52 PM
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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.
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1987 VW Jetta Mk II - Daily Driver
1992 W201 2.3 - sold
1985 W126 380se - sold
1985 W123 OM617.952 - sold
1981 W123 OM617.912 - sold
1986 W201 2.3 - sold
1979 W123 OM 617.912 - sold
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  #5  
Old 09-26-2008, 10:25 PM
t walgamuth's Avatar
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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.
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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.
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  #6  
Old 09-27-2008, 09:55 PM
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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?
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  #7  
Old 09-27-2008, 10:17 PM
t walgamuth's Avatar
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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
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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.
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  #8  
Old 09-27-2008, 11:03 PM
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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.
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1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR
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  #9  
Old 09-28-2008, 09:11 AM
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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.
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  #10  
Old 09-28-2008, 12:35 PM
High River Alberta Canada
 
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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.??
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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR
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  #11  
Old 09-28-2008, 06:50 PM
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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.
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  #12  
Old 09-28-2008, 07:49 PM
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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!!!
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  #13  
Old 09-29-2008, 07:09 AM
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I am thinking about that too. I'll probably take whatever I can find first.
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  #14  
Old 09-29-2008, 07:38 AM
ForcedInduction
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Don't forget about speedo correction.
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  #15  
Old 09-29-2008, 05:50 PM
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Quote:
Originally Posted by ForcedInduction View Post
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.

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