w115 om616 240d

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

change differential w123. http://mbturbo.com/how-to-change-final-drive-w123/

When i searched for instructions, I could’nt find any, so i took some photos during my change, hopefully it will help some of you with your projects.

Instructions how to change on a w123

Compatible final-drives

Finding a new differential with a better gear ratio isnt that impossible for us with /8, since the differential is the same on a w1114, w115, w116, w123 and w126 (untill 1984) after 1984 the w126 diff doesnt fit. so a 1984 w126 will do just fine, a 1985 won’t

the diff I am about to use is a 2.65:1 comming from a w116 6.9 thats the one to the right, and i stole the yoke from the diff to the right

When shifting final-drive to one from a v8 car, you have to change the flange (the thing you bolt to the hardy disc) since the flange are bigger on the V8s, when changing the flange you will have to get data on what torque the bolt

Changing differential on a stricht acht

Start by getting the wheels up from the ground, and remove the bolts holding the driveshafts, on my w114 from 1968 the bolthead was 17mm, on my w115 230:4 it was 13mm, so there is a difference in driveshafts, so dont toss the bolts away if you have spare ones. I hope the splines should be the same, something i will find out tomorrow otherwise.

Remove the exhaust and the bolts connecting the yoke to the hardy-disc, this is important to do before removing anything else

17mm nuts, and 15mm bolts, these are finethreaded m8s if i remember correctly

use a prybar or something else to get the flanges free from the disc, the disc has these parts that moves into the flanges when tightened, if rusty, they will stick good, and be a pain in the ass to get loose, dont give up.

if you dont remove this before lifting the diff down, any bending will go to the rubberthingy holding the cardanshaft in place, those are prone to brake, so unnecesary force on those is prefered.

Flexdisc failure w123 superturbodiesel (2)
I also got the jack in place, since it’s needed later on anyway.

Remove the matt in the trunk, at the far end you will find four holes (hopefully covered with something)

Remove the plastic/rubber over the four holes and loosen the four nuts

these nuts are 19mm in size, and for the two furthest in you will need something like this
The back of the seats in the sedan makes it impossible to use a regular socket-wrench and it is way to tight to unscrew the nuts from underneath the car, unless you put a jack under it, removes the four m8 bolts and slowly lower everything, this is necessary on a w123 chassi, since they dont have the holes to acces the m12 from the trunk.


Next step is to loosen the four m8 bolts (13mm) that holds both the final-drive and the suspension in place, without the jack underneath the finaldrive, the whole thing will fall towards the ground, potentially damaging the driveshafts. it also makes the unscrewing a bit harder if the final-drive is constatly pressing against the bolts.

Didnt take a picture while taking down the differential, i lowered it a bit and used a metalpipe to knock on the driveshafts so they got out a bit, lowered, knocked, lowered until the driveshafts was loose, be careful not to damage the “brakepipes”

Here i have a piece of bord holding the exhaust up, as well as on jack holding the suspension “bar” up, without the jack in place, the springs will push the “bar” down, the jack has to be in place the whole procedure of lifting down the final-drive.

it doesnt realy if you have the car high up, but i found it easier to get the four studs on top out of the bar if it didnt flex, as it does if you let the springs push it down.


5 thoughts on “Final-drive, how to change w114/w115”

    1. thanks, this was the first diffswap i did, and unfortunately i havent updated it much, it lacks a few hints and tricks, but will get them in there soon i hope.

      its pretty much straightforward
      1. lift car up, remove tires
      2. get exhaust down, remove the calipers (easier to get the driveshafts down)
      2.5 remove the 13 or 19mm bolts holding the driveshafts in place in the hubs, use a hammer to “get them loose” if they are tight.
      3. loosen the hardydisc/flexdisc 15+17mm bolts. pry it loose, or hammer it if you are putting a new one in.
      4. get the four 19mm at the top, or get the four 13mm at the back, if you go in throu the trunk, keep the 13mm in place, if you go from below, start with the 13mm.
      4.5 use a jack so the diff dont drop down and brake your teeths when loosing the 13mm at the back.
      5. remount the oposite way

      if you go from below for the 19mm at the top, the procedure is more like the w123,

      its a matter of taste, and how well aligned the holes in the trunk are.

      where do you live? im in sweden, and a w123 cluster+ headlights for a w115 would be expensive to ship, what do you need?

    1. the 350SL r107 or 350SE w116

      you could also use the 300d/300td w123 but then you will need to swap the yoke/flange since the v8 are bigger.
      i dont know, but i think the 3.46 from the 350SE has the bigger flange, but might be the smaler housing.

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