[W126 Coupe] Help! : diff ratio's

[Divov]

Thanks.
I understand from other posts that the diff casings are the same between the 500 diff and that of the pre '80 450SEL & SL and it is a simple bolt in job.

Rummaging thro' the shelf full of diffs at the breakers yard, there were the diffs with the big squarish mounting rubber situated aft (that's my 500 type diff) and then an equally large diff with a big horizontal hole in an aluminium casting on the rear which was obviously some alternative mounting arrangement (and without the squarish mount). Then there was a 3rd diff which was considerably smaller coming from the smaller Mercs.
My understanding is that the 350SE diff is externally identical to the 500 diff but I will only be stripping that 350SE diff out on Tuesday and then I will know for sure.
Assuming that I am right & the casings are identical and also identical to the 2:47 LS unit, then I would have hoped that the crown wheel & pinions would be interchangeable as the diffs are a perfectly simple bolt-in job - But this is a wild guess & I hoped someone had been down this road already.
Regards
Alex

  ----- Original Message ----- 
  From: Steve Nervig 
  To: Mercedes Coupes Mailing Lists 
  Sent: Sunday, April 29, 2007 3:18 PM
  Subject: Re: [W126 Coupe] Help! : diff ratio's


  Alex, first off, let me say that I am not an MB diff expert, so verifying what I say would be a good thing.


  My understanding is that MB has generally had two sizes of differential housings and gears. There is a smaller size (1.0 or 1.1 liter oil capacity, 185 mm dia ring (crown) gear) and a larger size (1.3 liter oil capacity, 210 mm dia ring gear). There also appears to be some changes within these two categories. See Job 35-500 for some visual clues on differences. 


  My belief is that the two sizes are not interchangable as a unit in a particular chassis because of mounting configurations and that the gears are not interchangeable between housing sizes.


  I've heard that the smaller size generally came on cars with less than 200 HP and the larger size on cars over 200 HP.


  I've also been told that changing or installing a gear set in a housing requires a special tool jig set and can't be done properly without it. In the past, I've set up rear ends (non-MB) with shims and machinist blue, but apparently this isn't how an MB rear end is set up. Something about crush washers on the pinions seals. How an improper set up would manifest itself, I do not know. Maybe you could get by with it for limited racing, and the only problem would be a leaky pinion seal. Maybe not.


  So apparently, the trick is to find a suitable donor car that has the same configuration housing and replacing the whole thing, without opening up/changing the gears.


  I'm sure there is someone who can either confirm or poke holes in the above statements.


  Regards,
  Steve Nervig




  On Apr 29, 2007, at 3:54 AM, Divov wrote:


    This website is just great!  Without it I would be floundering around in the dark.
    Thanks to the various inputs, I have located a 3:46 diff from a 80 350SE saloon and the best of it is that it is available free, gratis & for nothing!!
    Now, what I am scheming is the following:
    This 3:46 diff is not LS so what if I take the 2:47 LS diff available from the friendly scrap yard and strip the crown wheel & pinion from the non LS 3:46 diff and fit that into the LS unit. Is this do-able? Does anyone have experience of whether the crown wheel & pinions are interchangeable?
    Thanks guys.
    Alec D
      ----- Original Message ----- 
      From: Barry Corno 
      To: Mercedes Coupes Mailing Lists 
      Sent: Saturday, April 28, 2007 5:45 PM
      Subject: Re: [W126 Coupe] Help! : diff ratio's



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      From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Divov
      Sent: Saturday, April 28, 2007 8:21 AM
      To: Mercedes Coupes Mailing Lists
      Subject: Re: [W126 Coupe] Help! : diff ratio's



      Thanks for that tip Barry.

      I take it that it is also the diff with the big square rubber mounting situated aft?

      Its good to know that such a ratio exists but down South, SL spares are pretty thin on the ground.

      Would the 450SL have this type of diff or is it only from the 500SL?

      The 450SL is an absolute dog but a friend had a late 500SL (same shape as the 450) and though it was years ago, 

      I recall the acceleration was reasonably impressive from the passenger seat.

      Do you know if your 3.07 diff is an LS diff?

      AD



      Alex,

           My 3.07 is out of a 450SEL “78”. I believe it is not LS, but someone on this site would know

      For sure. 450 SL’s have the 3.07’s.You need to know that you will be turning around 3,000 RPM’s

      Around 65 MPR and your speedometer will need to be re-calibrated.

      Gary Dempsey has put 3.07’s in his 560. What a difference in that car also.



      B.C.

        ----- Original Message ----- 

        From: Barry Corno 

        To: Mercedes Coupes Mailing Lists 

        Sent: Saturday, April 28, 2007 4:52 PM

        Subject: Re: [W126 Coupe] Help! : diff ratio's




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        From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Steve Nervig
        Sent: Saturday, April 28, 2007 6:46 AM
        To: Mercedes Coupes Mailing Lists
        Subject: Re: [W126 Coupe] Help! : diff ratio's





        On Apr 28, 2007, at 5:46 AM, Divov wrote:



        Dawid,

        The 500 is really a bit of a slouch off the line. The 560 is a rocket in comparison.

        My 500 (at highveld altitude) does about 230 kph in 3rd (at 6000rpm) but max'es out at only 240 in top. At 240 it is only revving around 4200...

        The 500 mill is free revving and goes to red line willingly (except in 4th!)

        That 2.24 diff ratio on the 500 really really makes it an old mans car. 160 kph @ 2900! - its hardly working up a sweat.

        Your 560 does about 7 sec  0 - 100 kph & is way, way faster. I think partly from more beans & partly from 

        better ratios.

        Clearly the 560 was aimed at being more sporty - and certainly is.

        I have only 170KW vs your 220KW. That's a serious difference... 170 KW moving 1600kg aint no ball of fire.

        Alec





        Alec, it seems like you would benefit from an even lower rear end (higher numerically). You mentioned that you were going to try to find a 2.65, I believe, to replace your 2.24? Isn't there a 3.07 available and wouldn't that be even better?



        I know Barry Corno's 380SEC really improved in acceleration with the change to the 3.07.



        Steve





        April 28 2007

            Steve is right on the improvement. I did loose 1 ½ mile per gallon, but have picked it back up

        With cats removed.  It is a cheep fix for a 380 PIG. On the pre 86’s it is a bolt right in Diff from

        Any pre 80 SL or SEL.



        B.C. 380 SEC AMG  514K


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      The MB Coupes Website!
      W126 SEC Mailing List
      Postings remain property of MB Coupes, L.L.C.
    The MB Coupes Website!
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    Postings remain property of MB Coupes, L.L.C.




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  Postings remain property of MB Coupes, L.L.C.
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