3.27 Diff. for my 240D Turbo - PeachParts Mercedes-Benz Forum

Graminal95 · #1 08-13-2008, 04:19 PM

Well I just bought a 3.27 diff. from a euro 380slc and am waiting for it to arrive. I was hoping to get a LSD from a 450slc my buddy had and swap the ring gear but no luck, it was an open diff.

I'm heading off across the country in a few weeks and wanted to be able to cruise on the highway quietly. I have a 3.69 in there now and could have gotten a 3.47 but thats only a 6.3% difference where as a 3.27 is 12.8%. I have access to a 3.06 but I think its going to be to tall for the 240D at 20.6% so I'm hoping the 3.27 will be a happy medium.

So at 65mph thats 3350rpm for a 3.69, 3150rpm for 3.46, 2950rpm for 3.27. I figure that with the addition of the turbo, and about 40% more power, the 12.8% reduction in mechanical advantage should still make my car faster then a stock 240D, I hope

I just put a new clutch in a found out that the release bearing is the earlier type which is 6mm longer and will not allow the fingers on the pressure plate to fully relax allowing full lock up.... so out comes the tranny again.

Anyone need an early release bearing with about 5min of use?

bgkast · #2 08-13-2008, 04:50 PM

I calculated that 1st with a 3.07 from a stock turbo car would be close to second with a 3.69 rear. The 3.27 will be even worse than second with the 3.69. It will be rough on the clutch and hard to start on hills!

t walgamuth · #3 08-13-2008, 05:46 PM

No the 327 will be better than a 307.....this probably will work ratio wise unless you live in San Fransicso and have to take off on very steep hills....

if it will fit.

Tom W

bgkast · #4 08-13-2008, 05:54 PM

For some reason I read that as 2.27.

Is there such a thing as a 3.27?

Graminal95 · #5 08-13-2008, 06:00 PM

I think your going the wrong way with your calc.

Just think about it like this, (not trying to be condescending, I just write like I speak)

MPH = RPM * Tire Diameter / Gear Ratio * 336

So lets say second gear with a 3.69 diff. that 1000rpm * 24.2in / (2.32*3.69) * 336 = 8.41mph per 1000rpm

then lets look at first with a 3.27 so 1000rpm *24.2 / (3.91*3.27) * 336 = 5.63mph per 1000rpm

8.41321
Or a 3.07 diff. in first is 1000rpm *24.2 / (3.91*3.07) * 336 = 6.00mph per 1000rpm

Or if you take 3.69 / 3.27 = 1.128 or 12.8% then lets take first with a 3.69 1000rpm * 24.2in / (3.91*3.69) * 336 = 4.99mph per 1000rpm then add 12.8% or multiply by 1.128 and we get 5.63mph per 1000 rpm

In this way you can take any diff. ratio and find out how much faster or slower % wise your engine will be turning for a given gear and mph.

so its not that much faster take off wise, as max speed in first will be ~28mph instead of ~25mph

Graminal95 · #6 08-13-2008, 06:02 PM

Oh, well then excuse all my maths, 2.27 would be crazy on the clutch......

3.27 only came in the R107 380sl/slc in europe so a rare find and hopefully a good find, but I won;t know till it gets here

winmutt · #7 08-13-2008, 08:21 PM

Quote:

Originally Posted by Graminal95

Oh, well then excuse all my maths, 2.27 would be crazy on the clutch......

3.27 only came in the R107 380sl/slc in europe so a rare find and hopefully a good find, but I won;t know till it gets here

I will get a 2.47 pretty soon I think. About the LSD diff, what was it geared for? Are you sure it will fit?

Graminal95 · #8 08-13-2008, 08:49 PM

The LSD came on some euro SL's and the 450sl that my buddy had did not have an LSD. If it had I would have pulled the diff. apart, taken the diff out of the LSD case and swap the ring gears over and then set up lash..... the older diffs had lateral bearing caps that could be removed and shimmed to set lash and bearing preload.... but on the later ones like most of us have, the case has to be stretched to give the proper preload on the bearings. This makes messing with the internals a huge pain even with the right tools.

A 2.47 with a manual tranny? Do you have a funny first like the post 83 cars have?

I will be interested to see how the clutch holds up, and how your hills starts are.

rudolfgreen · #9 08-13-2008, 10:23 PM

Mutt dont you already have the 2.88 back there?? AFAIK the manual ratio is different from the auto.
The 2.47 might be too low with the manual trans, but the 2.65 might be sweet.

#10 08-14-2008, 12:26 AM

A 3.27 would be about perfect for a manual with turbo. too bad there are no speedos that will work with it in a W123.

winmutt · #11 08-14-2008, 08:27 AM

The manual and auto gearings are fairly similar, not sure what you mean by funny first? I do already have a 2.88 and have no problems starting up the fairly decent hill infront of my house. The 2.47 will follow the VNT install.

Graminal95 · #12 08-14-2008, 10:22 AM

First gear for post 83 240D's were 4.23 instead of 3.91.

2.88, damn I would have figured that it would be to hard on the clutch but I guess not.

I calc. out that first gear with a 2.01 diff would be the same as second gear with a 3.69. I know I can start in second gear, but its hard on the clutch, so I guess 2.88 should not be to bad especially with a 617.

winmutt · #13 08-14-2008, 11:13 AM

As I said 2.88 is just fine. However I have a 5 speed I plan on installing one day, looks like 2.47 will be out of the question, I may end up with a 3.27 even.

Interesting tidbits on the LSD. Ther is an aftermarket solution but I have heard poor reviews. How different is the LSD case that it requires swapping the internals out.

Graminal95 · #14 08-14-2008, 08:57 PM

The LSD case is the same, I was going to swap out the diff itself so I would have the 3.27 ring gear on it and not the 3.06 that it had originally. If I had wanted a 3.06 and LSD (and the diff, was actually an LSD and not open) then I could have just bolted it in.

Is your 5 speed a proper one from a w123, or out of something else like a BMW....

Graminal95 · #15 08-25-2008, 10:16 AM

Well I just got my diff. today and they did not clean the diff and check the ratio as they stated.

Q: Can you tell me the gear ratio for this diff. Its stamped on the lower left of the rear cover. It should say something like, 3.46 or 3.06.... http://www.peachparts.com/shopforum/attachment.php?attachmentid=56235&d=1214319835 Aug-08-08 A: 3:27

http://picasaweb.google.com/GWCullen/EbayDiff/photo#5238453569071438018

and it turned out to be a 2.47!!!! Great just what I need for the 240D!!

http://picasaweb.google.com/GWCullen/EbayDiff/photo#5238453657081549554

What do I do now?

I tried calling the seller but the phone line has been disconnected, of course.

I hope he responds and says he has the right one and it will be overnighted to my door, but I don't think that will be the case.