w123 om602 turbo coupe

Different gear-ratios in differentials http://mbturbo.com/gear-ratios/

change differential w115. http://mbturbo.com/how-to-change-final-drive-w115/

I am changing the rearend on the coupe, from the 3.58 that came stock with the original 280CE engine, to an 2.88 i got from Garrett Sowards in Sacramento,

removing differential w123


removing the differential on an w123 is a tad harder than on a w115, or maybe it is just that i am more familiar with the way the w115 works.
(the w115 has these holes in the trunk that makes it possible to loosen al four bolts on top of the differential without breaking your wrists or not having enough play to acctualy use a long arm to get them loose)

either way, in the order i do it.

lift the rear of the car up, make shure it stands secure, remove tires, and any exhaust system that might be in the way of the driveshafts.

loosen and remove the bolts from the flexdisc, 17mm and 15mm wrenches is needed, i would suggest you make shure the flexdisc is loose from the flange, as it could be a pain in the ass to get them seperated when you are laying with the differential ontop of you and everything else is loose.

remove the four bolts at the back, with a jack underneath, lower it down

try and loosen the four 19mm bolts that holds the differential up to the “subframe” or what its supposed to be called.
i found it easier to remove them from the back of the car, instead of trying to do it up between the Cardan-shaft

this tool worked perfectly for me, was just long enough to reach the bolts at the front over the arm ****’…

tools rearend

the long for getting them loose, and the shorter socketwrench to be able to reach from the back, se the other picture

you also need a 15mm and 17mm wrench (and i use a 15mm socket and socketwrench) to loosen the cardanshaft from the yoke.

+ 13mm socket to loosen the four bolts that holds the whole ordeal up.

9 thoughts on “Final-drive, how to change W123”

  1. I have been wanting to do this for years on my W123 280E from 1981. It has an OEM differential with 3.69 and it is awful to drive on the highway plus the MPG. If I am lucky I get 20 MPG. Anyhow I bought a differential that has 2.47 gears in it of a R107 approximately the same age. My car has 566K miles and the 2.47 differential I am told 105K miles. What I hope to accomplish to drop the RPM significantly. It has been awhile since I drove the car on the highway but I recall that it would do 4000 RPMs at barely 80 MPH. I hope to reduce the RPMs a lot with this differential. Will keep you posted and maybe you have an idea how much it would drop. I did look at 2.27 differentials as well and read through so many blogs that it was much bigger and drive shaft had to be shortened.

    1. hmm, yeah the 3.69 is very high geared.

      make shure you have acctually bought a diff from a r107 before 1986, since they after that get a different layout that wont fit your car.

      the car will do like 60mph at 2000rpm with the 2.47, it will be more sluggish, especially since the m110 is a rev-happy piece of machine

      the 2.24 is a tad to low, a 2.47 might be to depending on how you wish to drive it, but i am very certain that you will get better mileage,

      no, the 2.24 isnt sizewise any different than the 2.47 or 3.69. in terms of cardanshafts etc, althou the gearings are bigger.

      if you get the diff from a v8 from a w116, w126 or r107 you will have to swap the yoke/flange. either you change, and do it by feel, or get a shop/or yourself to correctly torque tighten it in place. many people have been succesfull with the “plug/play” way, but i do it the real way.

      to do it correctly you have to swap a “bushing/washer” that is “crushed” and keeps the bearing at the correct torque, a way to go around that is to, get a NM when loosening the stuff, and then retighten it a tad tighter.

      thats how ive been told, and have learned it by experience anyhow.

        1. the 240d w123 is supposed to have a 3.69 differential stock, althou, there shouldnt be an issue going for a 3.46 from a 300d.
          i run the same engine with both a 3.07 and a 2.88 differential

    1. yes, besides the swap of the yoke.
      done both w116 2.69 and w126 2.47LSD diff on two w123s.
      aswell as one 3.27 w126 on a w123

  2. 83 280ce Euro RHD swap 3.58 to 3.07 makes the car lazy from standing upto 30mph but 3200rpm at 80mph so quieter on the motorway and more interesting to drop down from 4th the 3rd at 60pmh as its more responsive between 40-60. Mpg is the same on combined as what you gain on at high speed, you lose pulling away. 19mpg around town and 23mpg on a long run

  3. I’m having serious thoughts about getting a 3.07 that the 300D Turbos had thru 1984 for my ’83 240D with manual transmission. I found out that my 240D can only do 80+ mph downhill and top speed flat out is now only 76 mph on level ground. So I can only conclude that a stock early 80’s 240D with stick shift could only achieve a top speed of 84mph or so on paper. At 70, it’s felt that it maybe had a little bit left in it, I thought maybe 10-12 mph left. And I’ve read stories about owners of those gutless 240s being able to cruise at 70 or even 75 all day. So, if it’s possible, how much money would I look at spending for it? It’ now becoming due for a rear end service and some work on it anyway. P.S. I’ve enjoyed proving that there’s at least part truth in those diesels being built to go fast and run forever.

    1. i have two w115 with the 240d engine from the w123.
      one has the 3.07 diff, the other a 2.88 diff.
      both works and drives good, and i have no problem reaching 70mph on flat ground, 80mph might be the end of it thou.

      id look at valves, fuelfilter and airfilter of your engine. clean the one in the fueltank aswell.
      Some people praise the sea-foam, althou i havent tried it myself.

      depending on where you live it might be more or less easy to get ahold of a 3.07 diff, in europe significantly harder than in the US.
      Where do you live, i have a friend in California who has helped to send multiple diffs to me for reasonable prices, he also does work on the w123.

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