Well - I have found the MB diesel "easter egg"
 

Some of you may know that an "easter egg" is something cool hidden in software (basically). Well I think I may have stumbled upon something that the MB engineers may have hidden in the MB diesel. I swapped out the rear end with a 300 SE. I can't believe the difference! Instead of running at 3K at 65 its just a hair over 2.5K, right at the edge of the turbo catching - absolutely perfect for cruising at 100 where before I was afraid of blowing the engine. Even the 160 MPH speedometer dropped right in without any recalibration (hard to believe). I know what you are thinking - damn that thing is slow off the line now - the funny thing is it seems like this is a whole new car - instead of shifting from second it will always start in first and run through the gears - once the turbo kicks in it will work any other 300SD on the road! (well, have only tried her against the roommates car). It seems this may have been the rear end that was originally designed for this car and they had to change at the last minute. I always knew something was a bit off. I have been working on these cars every day for a long time now and this is the best thing I have ever done to one. Why did they do this? Was this a US requirement or did they not want the diesel 5 model to be faster than the gas 6? Hmmm I would like to talk to these engineers….

What year model was the SE?

I'm not sure - it could have been a 380 SE too. I bought the rear end awhile ago from a member on this site. One small note: This morning I got to try it out on some fresh snow - Didn't fare as well as the low rear end but once you are going its all good - probally be fine with some snow tires as I am running bald summer tires .... (car is getting ready for some major upgrades and restoration - photo is new interior)
I will try to get some shots of the rear end next time I have the car in the garage.

seats (excuse the dust :( )

Perhaps you're too young to remember the 55mph national speed limit that was in effect when these cars were built. MB tuned them to have the sweet spot between 55 and 60.

Yes I am far too young to remember those times, this car happens to be the same age as me. It seems like the rear end they fitted to the car was not tuned at all, always starting in second gear and already in fourth by fifty or sixty. I think that may have been a quick fix for some government-supplied law, no? The SD was a US only car correct? They only had the 5 CYL turbo in the euro 123s? I have seen a couple 123 diesels that drove like this perhaps the SD was so de - tuned because of the US only status? I am just very surprised that with a simple gear change the car feels like it is finally in balance. Each gear shifts at the perfect point right back to ~2500 all the way up. Definitely hits the power band of this engine like I always thought it should be. As you can tell I am very excited, I was working on replacing the tired automatic with a five speed for this very reason, now I think a rebuild is all she needs….

Yes, that is EXACTLY what they intended! 2nd gear start was to improve fuel economy. And the car had to be in top gear by 55 because that's as fast as we were allowed to go - anywhere in the United States, ever! In the mid 80's I had a job that involved travelling to Ft. Hood, Texax. I was advised to drive 53 mph on INTERSTATE highways in TX, because 56 would get me a ticket. Times have definitely changed.

hee i do remember those days. if you had a yankee plate you had better slow down to 55 or below when you hit the mason dixon line going south:D
it took soooo long to get to florida in the bug:eek:

I'm very interested in this. How difficult was the rear end swap? Was this a weekend job? Did you swap out the rear end housing or just the differential and assorted other gears?

How did you adjust the speedometer? How was the top speed affected? Has MPG changed much? Last question for now, what is the ratio of the SE gearing? :confused: :confused: :confused:

Can you give us the final drive ratios of your old and new pumpkins?

Cool!!!! I have a 380 SEL parts car and i would love to do this!! Do you really have to change out the spedo too or can you leave the factory one in?? Also what kind of fuel economy could you expect doing this?? 35mpg??

Me Too!! Me Too!!!:D :D

The 85 300D had a way taller rear gear as well, I've wanted to know what one felt like. I feel the 300D's are geared way too low as well. Though we don't have the second gear problem..

R107
---------
380SL,SLC RATIO 1:2.47

380SL,SLC,560SL RATIO 1:2.47 ABS

450SL,SLC RATIO 1:2.65

450SL,SLC RATIO 1:3.06

W116
----------
280S,SE RATIO 1:3.69

300SD RATIO 1:3.07

450SE.SEL RATIO 1:3.06

450SE.SEL RATIO 1:2.65

W123
----------
230,240D RATIO 1:3.69

280E RATIO 1:3.58

300D RATIO 1:3.46

300DT 85 RATIO 1:2.88

300DT TO 84 RATIO 1:3.07

W126
----------
300SD 85 RATIO 1:2.88 ABS

300SD TO 85 RATIO 1:3.07

300SDL RATIO 1:2.88 ABS

300SE,SEL RATIO 1:3.46

380,500 RATIO 1:2.47

380,500,560SEL RATIO 1:2.47 ABS

420SEL RATIO 1:2.47

W124
----------
260E RATIO 1:3.27

300D 1987 RATIO 1:2.65

300E RATIO 1:3.07


Here ya' go fellas....Good reference, I suppose.:)

Just to clarify. The numbers 85 and 84 in the list above represent years 1985 and 1984 correct?

Yes..,

When considering a rear end swap one has to also consider the tranny ratios. Did MB change ratios of the automatics between cars in the same class (W123 for example) Did they change them much between models with same engine (W123 vs W126)

Sorry I know I should know some of this. Im still trying to stuff all this into my head. If someone has a list of trannies I will try to find time to make a spread sheet file with rear end and tranny's listed together if folk think it would help.

So it was a 380SE diff. That makes sense. I had a 300SE and it felt like the engine would hit redline before 100mph. The dragstrip crowd will pay plenty for a 300SE diff :)

Sixto
95 S420
87 300SDL

Well it seems it was a 380 SE then. The swap was very simple. Pulled the old one out, switched the input yoke with the smaller SD one, bolted everything back in and dropped in the 160 MPH speedo. Nothing more to it.

Oh and just so you know my old rear end was that of the 80 300SD, according to the chart 3.07. No wonder she feels a bit different....

How have your 0-60 times changed?

I have not yet checked 0-60 but I will post results soon.

Where did you find the rear end ratios? I have an '84 230e clunker that I would use as a rear end donor for my 300d if I thought it would make a difference, but I don't see the 230 listed. I think the car originally came from Canada, not the US. How can I find out the rear end ratio?
-andy

I found a whole bunch of rear axle ratios in the 123 and 126 model CD's. I'd scan and post but it would probably take four separate posts.

adsitco.com

Here, click here!

Actually, the 230E has the same differential as the 240D. A 3.69! That old 4-banger must be pushing the revs out, huh?

Thanks for the adsitco post. A lot easier to understand than the MB Manuals.

I don't care how cold or how much snow there is, I'm hitting the junk yard this weekend!

Here's another link to an online calculator of tire size:

http://www.miata.net/garage/tirecalc.html

Take the height of the proper tire and plug it in, and figure out MPH with the different differentials at certain RPM, go to

http://www.prestage.com/Car+Math/Gear+Ratios+and+Tire+Sizes+/Calculate+MPH/default.aspx to figure it out. Very simple to use.

Its very accurate...:)

Oh, so a four speed 240D will hit its 5400'ish governed redline at about 105 mph with size 185/70/R14 tires.

A 300D with a 3.07 should go up to 123 mph.

etc., etc.,:)

FWIW, my 83 300TD and 84 300D both have 3.07:1 final drives.

Only one problem with that 240D calculation - it doesn't have the power to get there! Factory reported top speed for a 240D is 84 mph. Mine is especially strong, and will bury the 85 mph speedometer, but 105 is verrrrrry optimistic.

True, but if you get a long slope downwards, a 240D should be able to reach it.:)

I'd LIKE to see an '83 240D showing 105 mph on the speedo!

I can get the rear end from a 380SEL in a local salvage yard. The Adsitco site lists it as 1:2.47 ABS. Will the ABS part make any difference? Will being taller than the '85 'Ds 1:2.88 and my current 3.07 be too much for my little TD?

Side question: Is there a DIY way to recalibrate the mechanical speedo?

115
 

Can I use a 123 reareand in my 115 240d or is there a 115 rearend that will work better?

I am assuming the 115 240d will have a 3.69 and I will want a 3.07.

Surprise
 

Look what I found

Used Differentials : 115

Model/
Description: Notes:
Part Number:
220D,240D RATIO 1:3.92 135-1510
280,280C,300D RATIO 1:3.69 135-1511

:eek:
No wonder the 4 banger is really banging at 85. I will check mine and then look for a 3.69 or 3.45.
Thanks,
Brian

The 116.036 rear is the 450SEL 6.9.:D I would like to change my
3.07 to somthing around 2.65, to lower rpms some.

A 2.88 is fine. I mean, where are you going to go 130 + mph(if you can get there)? A track perhaps? That's about it!

In the Spring(in New England, Spring comes in June), I plan to take a car to the track, just to give it some excercise. Maybe record the whole thing on DV. I don't care about racing, I just care about letting the poor things stretch their legs once in awhile.:)

I guess I should worry about going 130 + mph, since I only have "T" rated tires on my cars.:eek:

If the 3.69 rear end from the 280C I can get to is good, I wonder if it will help the 20.9seconds my TD did at the 1/4 mile...

Does anyone know if a rear differential from an 1986 560 fit into a 116 1980 300SD without any problems?

In 1985 the 300D Turbodiesel came with a 2.88 gear. It also came with a higher stall converter.

My 1984 300D Turbodiesel came with a 3.07 gear. In 1990 I modified the air filter system, which reduced lag and improved performance. Details of this are well documented in this forum.

In 1999 based on information from "Stu Ritter" in Colorado I replaced my torque converter with a 1985 model with a higher stall. '82- early '84 have a smaller pilot hole for the torque converter. Late '84 and '85 crankshafts have a 35 mm pilot which this torque converter fits.

I attribute my off the line performance, smoke right rear with ease, to this modification.

I drive the Florida Turnpike alot at speeds up to 95 mph. The 2.88 gear would be extremely favorable for sound reduction, reduced engine wear and fuel economy. But to give up this acceleration would be a crime.

I believe the stall difference is 400 rpm's higher.

Did you have to have the pilot end of the torque converter to
fit the smaller hole?

No the crankshaft on my car had a 35 mm hole. Lucked out

I have an '85 300DT and I didn't realize that it had a 2.88 rear end. I always thought it had the 3.07 since at 75MPH the engine seems to rev fairly high. My tach doesn't work so I have no idea what the RPM's are. I go up a fairly steep hill on the way home and it does fine. Off the line its OK. The MPG's though are nothing to brag about. Last fill up only got me 21.8 MPG. That's my usual average.

My fuel economy is a consistent 20.85, city highway combined.

Re: Well - I have found the MB diesel "easter egg"
 

OK, I have the opposite problem, I have a 300D (NON-turbo) with a poor acceleration. I would like to increase the ratio, to allow better acceleration. I don't cruise at more than 70 mph, so there is no risk of engine damage due to over revving.
I would also like to keep the Speedo and odometer calibration accurate.
How do MB adjust for the different ratios, effect on the speedo?
If they use different speedo drive gears, are they sold as a set? or a single piece?
How else could they do it?
Is the answer to buy a speedo calibration kit (for rallye cars) and set the cogs to compensate?

I have found two 280SE (One 2.8L I-6 and one 4.5L V8) (W108) in a salvage yard. The rear ends are marked 3.92 and 4.08. In my quest for better off the line perfomance I must ask, will these swap into a W123 with little fuss? Next to the 280's there is an '85 300D with the 2.88 rear. I may be willing to pull it and ship it for somebody.

I would love the 2.88, but I'm worried about speedometer calibration. Does anyone know if the speedometer from that 85 300D would drop into my 81 300TD without fuss, and be accurate? My TD seems to have an electric speedo (no cable).

82-300td: Did you note how many miles were on that 300D? My differential already whines like a *****; if I were to get a "new" one it would be nice if I could get a low(er) milage one that would (hopefully) be quiet ;). How much would it cost to pull & ship?

3.07 to 2.88 is very little change
 

3.07 to 2.88 is very little change. The RPM required for 60 mph will now occur at 64. This is probably less than your current speedo error. If You read high like mine does it will probably be more accurate afterwards.
I think the differential that Breckman installed was actually something like 2.67 or 2.46
I think the taller gears would improve my off the line acceleration with more time in first gear. Its pretty useless right now.