[W126 Coupe] diff feed-back

[Divov]

I went to the breakers yard & got an exchange diff from a W116 which has ratios 3:27 - 1
  1.. The diff is dimensionally the same  (or very similar) to the SEC diff  & mounting bolt positions and rear rubber mount  are identical & will mount straight in without problem.
  2.. The main difference on the W116's (450SLC etc) diff is that the driveshafts are not the same as ours & have splined ends which go into the diff whereas the SEC diff has flanges onto which the drive shafts bolt.
  3.. A minor exterior difference is that on the SEC diff the breather valve stands vertical and on this diff the breather lies at an angle. This is of no consequence.
  4.. On the W116 diff it is simple to undo the back cover plate on the diff and remove a surclip which allows you to extract the driveshaft and similarly, on the SEC (W126) diff, removing the surclips let you remove a short splined shaft which has the flanged ends attached.
  5.. The SEC (W126) flanged shafts can be fitted in the W116 diff (in place of the whole driveshaft) and the retaining surclips refitted and now the W116 diff is ready to be fitted into an SEC. Simple simple simple!!
  6.. When you remove the diff back plate you do not interfere with the gears or anything. There are no nasty surprises like springs that jump out etc. You just get a ring side seat view of the innards of the diff gears - without any risk of changing any settings etc.
  7.. The 450SLC diff is not an LS diff. The ratios are 3:06 - 1, not 3:07 - 1 as reported on an earlier thread.
  8.. I'm not sure where the 3:27 - 1 diff I found (on the shelf) comes from. I'm sure it is from a W116 because the rear plate has a part # starting with 116 whereas on our SEC diffs, that same part has a # starting with 126 on it. I earlier reported that the diff I was offered off a 350SE was smaller than our diffs & wouldn't fit.  Perhaps I was wrong as that car was standing in the muck and my enthusiasm for getting fully underneath was understandably limited!! I think possibly the different drive shaft arrangement may have been what made the diff look different.... so check for yourselves. Perhaps the diff I have now bought is the same as the one I got offered for free....
  9.. With a 3:27 - 1 diff fitted into my 500, I roughly calculate that my top speed @ 6000 rpm in top gear will be only about 210 kph which for racing, suits me fine.  Fuel consumption will obviously suffer in sympathy. For street use, the 3:07 - 1 would probably be a better option. This is the 450SL / SLC diff.
Good luck & I hope this info will be helpful to someone.
Alec D.
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