Hey all, well i have a w123

2 door coupe' 1985 with turbo diesel engine, however the car used to have a m110 engine in it, so the diff is 3.58 or something.

I got myself a 3.06 ( closest i could find for the 3.07 straight swap ) In Australia we didn't get w123 turbo 300D's, only NA, so the ratios are 3.46 on them all here.

Anyways so 3.06 ratio diff is downstairs. ( from a v8 engine 450slc )
https://mbturbo.com/gear-ratios/

I've read the guides here
https://www.peachparts.com/wikka/W123Differential
and here
https://mbturbo.com/how-to-change-final-drive-w123/

but i read that i may have to swap some spacers and a yoke ?

can anyone help with a guide for them with pictures/tips or something please ?

it would be greatly appreciated. The engine makes too much unsettling noise down the highway with this diff.

3.58 m110 ratio to a 3.06 is a 17% reduction in engine rpm

so 4000rpm down the highway/motorway is now 3320rpm, should ease up on fuel consumption and keep it closer to peak torque for everyday driving.

Also, it is a 4 speed manual, so each gear should last longer before needing to change and i wont be crying for a 5th gear as much

Why not go even lower and get a 2.88 diff or one from a 380sl with a 2.07 diff?

there are still hills around here. Also, it's all what i could find. i looked at a dozen or so diffs and this was the only one under 3.46 ratio. Also didn't want to kill all accelleration

From the ratio guide that you linked, you can see that the oil fill volume for the 3.06 from the C107 is 1.3L, and the volume for your 3.58 is 1.0/1.1L.
The ring gear diameter of the 107 diff is 210mm, and that of the 123 is 185mm. Both diffs share a common mounting pattern, but the 210mm diff is wider than the 185mm. If the half-shafts from the 107 are used, it will all go together. Yes, the pinion yoke will have to changed to the one from a 185mm diff.

Thank you.

I saw this.

https://www.pelicanparts.com/More_Info/1233500410.htm?pn=123-350-04-10-M1192&SVSVSI=R107&KeepHeader=&ByPassCat=Y&null=

the same part for both the r107 and my w123 300D, says it fits both.

I guess the only way to get a difinitive answer is to try it and see how it goes and post back.

Your "definitive" answer will be to measure the width of the differential. As previously mentioned, one is 185mm and the other is 210mm. I swapped the entire axle/differential combo to eliminate sourcing spacers. You will likely need to replace the pinion yoke. Here is a good video from YouTube "university" that explains how:
Diff rebuild - how to set pinion bearing preload Ep.1 #1023
Andy the Mechanic

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

hmm,

would a w124 diff that is 185mm bolt straight in then ?

I'm doubtful because the mounting is likely to be different. The later models have a different subframe.
I've found the ratio for mine on a 420SEL. In the late 80's the subframe and differential mounting changed. I believe 80-85 or maybe even 86 had the same mount.

I dropped a 5 Cylinder Turbodiesel into my W123 (240D) with a manual transmission. The stock gearing spins the motor at an unnerving RPM; my solution was to bolt the differential out of a non-turbo W123 (300D) wagon - this was a direct bolt in replacement. I don't recall the ratio but it lowered the RPMs 11% or 12% (off the top of my head - again) the result was a blast to drive since nobody ever expected to see tire smoke from the diminutive 240. The swap required me to cut about 4" out of the front driveshaft and shift linkage and modify the transmission mount somewhat but it was WELL WORTH IT!

I have a 280CE that I put a turbo diesel in, and I left the 3.58 rearend in. But then I have a 5 speed in it, so when on the highway, the overdrive kicks in and lowers the RPM's to a comfortable level

__________________
Von
Fairport, NY
1973 Unimog 416 Doka
1980 Unimog 416 Doka
1981 Unimog 416 Doka
1984 Euro 280CE w/diesel conversion
1985 300TD Estate wagon
(I really need to stop buying these things!)
http://vonsmog.com

I have only a 4 speed :'( and 3.58 diff.

Instead of the yoke swap, i got a r107 driveshaft rear section from a friend and i measured it and it's the same size as the w123's one.


you said you swapped the entire axle/diff combo.


does that mean you just swapped the r107 diff as well as the 2 axles that go between the wheels and that's it ? and the 2 axles you used were the ones that came with the r107 diff ? as i have those, they came with it.


i looked up on wikipedia the r107 and w123 have a different wheelbase width, so i am a little concerned that even if i use the r107 cv axles, it will push the wheels out too far.

r107 = 70.5 inches
https://en.wikipedia.org/wiki/Mercedes-Benz_R107_and_C107


w123 = 70.2 inches
https://en.wikipedia.org/wiki/Mercedes-Benz_W123

1/4" ish isnt going to matter to the driveshaft length.
Get the rear shaft section, and it's all bolt up.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thank you.


All i need now is a new centre bearing as well as the rubber coupling thing ( name ? ) that goes between the drive shaft and the diff. I already have the rear drive shaft section from the V8 450.

So i'm looking for part numbers to make sure i get the right stuff.

....It's called a 'Guibo' and Peach Parts has it, I only use the original M-B ones as if it tears / breaks whilst underway, your car will likely be ruined beyond repair .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better