Yes. There was a makeover on the diff mounting starting with the US the model year 1986. All 1981-1985 w126 diffs should bolt on.

When changing the yoke on the Diff. and replacing the nut back on, you will have to set the friction pre-load. You will have to know what the preload is so it doesn`t get beyond what it was set originally. well maybe some for wear, but read this thread. this is the one that got it through the bone structure for me.

Arther Dalton mentioned a Torque O meter torque wrench. so I did a search on E-Bay to see what they looked like. Finally found one for $32.00 with shipping, and a Snapp-on.

www.peachparts.com/shopforum/showthread.php?t=233540

I have a 2:47 out of an 85 SE and one out of a 83 SEL. after 85 MB changed the Diff. mounting. don`t see how 86 thru 91 will fit a W123.

Charlie

Some MY 1985 500SEL's had the later looking diff with fins- they look like the genII w126 differentials. First gen w126's do not have fins unless they are on the rarer late model 1985 500SEL's.

the car I pulled this from had 88 500SEL written on the side by the yard. since I do not know the cars as well as most of you I assumed it was correct. Here is my finned differential mounted in my car. when I pulled this I verified it had the same mounting scheme as mine. I assume that others would do the same amount of checks assuming the knowledge needed for the scope of work to change the rear differential in a MB. I carried a picture of my diff in my phone to compare when I bought mine. sorry if my post was misleading, but someone said a finned cover differential would not fit and I can tell you that a finned one does fit. so instead of being critical in posts, please just add to the details. I never claimed to be an expert, I am just trying to share my little bits I have learned

I have an 85 SEL diff in my garage and it does have fins, Later model W126 diffs definitly will not work unless you manage to change the entire subframe.

My 84 SEC also has fins. on the back.

One interesting note, The 500 SEL and 500 SEC's have aluminium A Arms, while the 380 SEC, SEL, and SDs have steel A arms.

Here is a shot I pirated from eBay of a 420SEL diff. 2nd Gen w126s should have the same mounting points. But obliviously not the same as the w123, w116 or first gen w126.

http://www.peachparts.com/shopforum/...1&d=1231203857

There were 500's still made in 1988 but it have had to have been a euro model as none were made for the US market. That said, it was probably a mistake on the part of whoever marked the car.

See the attachment here for comparison of First Gen and Second Gen diffs.
http://www.peachparts.com/shopforum/attachments/tech-help/62313d1230080192-rear-differential-replacement-options-diffdifferences.jpg

Thank You guys so much for this. I have the 88 420 sel in the back yard with some of his buddies to keep warm with. It' s a balmy -53 degrees' celcius out there and the car is under a lot of snow... back tires flat and near impossible to see without a whole lot of work on my part to dig and jack. I could do it but have been sick for some months now and trying to conserve the energy for priority type of work. (essentials of life) so thanks for doing some of my "leg work" for me.

I have been out there in my unheated garage for a day and a half struggling with putting new rear axles in.
Did 'nt think this job was too difficult until trying to manouver under the car with many layers of clothes on. Fat belly. Gloves that impede dexterity. toque that kept falling off, frostbitten back from laying on frozen concrete. Can't hardly see because eyes are leaking some type of fluid out of them from the cold. Farts freezing etc.
I kept having to bring in my propane torch and aerosol cans of penetrating oil inside the house to warm up. I practically needed to spoon the old oil out of the diff to drain! (very thick).

I think the old axles were so hard to get out because the hub was shrunk more than the shaft of the axle in this cold weather. Everytime I hit it with heat the metal would frost up for a split second before actually warming the metal. A little heat goes a long way into getting these axles out and the new one's in was no different as far as heating the hub to expand for clearance. (makes sense if you think about it)
I used a small plumbers tip with a campstove sized propane bottle ,I think my next purchase is a tiger torch or a furnace!

As far as the actual job went aside from issues relating to working in extreme temperatures, it was straight forward with the help of this site and all the great advice.

I did run into one problem on the drivers side diff/axle seal.....it shattered.
Did they really make this seal body out of plastic?
I guess I must have bumped it the wrong way upon reassembly.(cold)
I only noticed because I could not get the c-clip on the axle . When I pulled it out there was a chunk of plastic binding it up. I put it back together with a large chunk of the seal missing but if this temperature holds up...I don't think that oil will be leaking out of there anyways, it is too thick.
I would like to put the new seals I will be purchasing into a new diff unit with taller gears if I have to do the whole thing again anyways. Will see if I can find one cheap. Parts cars are hard to find up here.

I know of a 82 300sd down the road...what size gears came in those?

Why can none of the parts places encountered find these seals?

No worries to Lutztd as far as his advice goes.... I am doing the research...right here. I appreciate your insight to the project you encountered for your coupe (nice wheels). You can never trust those junkyards and their regard for specific years to the vehicles they salvage. I am not out anything but in fact gained sufficient knowledge for this future project. I know you were just trying to help, it's not your fault, how could you know the year to be any different than what you were told by the guys you got the diff from. We challenged everyone to come together to answer this question if nothing else,thanks man.

With the pictures provided I am satisfied that this project will have to wait until I can get the proper year and style of diff. Clearly the 420 sel diff will NOT fit my w123 wagon chassis. The many exibits complete with pictures and illustrations explained this thoroughly.

Thank You all.

Next question...how hard would it be to swap the subframe out of the 420 sel into my 81 wagon?
Would it be too big being from a w126 chassis? I like the word resilient far better than rigid.

and I like anything but frigid for the next while.

I just checked my 83 SEL and 85 SE diff. and both have the finned covers.

Charlie

They should have 3.07, I have them in my 84 300D, but I much prefer 2.47.

A good comprimise is an 1985 300D or 300SD should have 2.88 and you can use a stock speedo from a 300D.

2.24 is also available but is too tall.

Icefire, did you change the gear in yours to 2.47? I love your car. I want to do the same only with a 85 up 6 cyl diesel and a 5 speed. but your color is exactly what I would look for in a car.

Lutz, I still have the 2.24 gear in my 300 SDC, the new diff in in my shop. Its winter here and I didnt want my SDC to get rusty so its sleeping in storage. First thing in the spring ill be installing the 2.47.

I ran a 2.47 for 2 years in an 85 500 SEL with 83 300 SD drivetrain. I was very happy with the comprimise between the takeoff and cruising speed.

When I sold the drivetrain from my "85 SDL" I kept the diff, so its going into my SDC.

your project sounds cool, I'd love to built an 88 CE, with a 603 and 5spd. I may get round to it sometime.