W123 differential - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 04-28-2017, 05:51 AM Thread Starter
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W123 differential

Hii Geeks,
I had recently swap my M115 engine to M102 985 engine with 5 speed manual trans, I didn't swap my differential and still using my old one for the M115 engine, I can feel that the acceleration is not that good and the car top speed also I think is affected 170 KMH which I think that the differential is the main cause so I need you confirmation on this, also I need you help to know what is teh best differential ratio to have as per my knowledge it is 3.69 is this correct

Regards,
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post #2 of 10 (permalink) Old 04-28-2017, 06:42 AM
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do you want better acceleration?
the only difference between your current fivespeed and the earlier fourspeed (besides smaler geardifferences in first to third gear) is that the new one has a fifth gear that lowers the rpm further.

the m102 in the s123 that came with a fivespeed (i had the 2.0 liter carburator in one car) had a finaldrive ratio of 3.58, and that would make the car a bit more sluggish than your current 3.69.

I would not say that the differential is the main cause, you are in about the same gearratio as the engine had stock (both in w123 and w124 chassis)
Since you have the 2.3 liter KE-jetronic version you ought to have some power in the engine, and i would not suggest going for a 3.92 differential that would be the next step for quicker acceleration.
I would guess the engine is the culprit, either something isnt working as it should, the KE-jetronic isnt setup correctly or your exhaust might be clogged (a catalysator that is old and limits flow can seriously slow an engine down)

you ought to have some power, 97kw (about 130hp) moves the car quite okay, i would look at the engine.

or do you feel it revs itself to much?
then there is options. but "acceleration" gets less good in that case.

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post #3 of 10 (permalink) Old 04-28-2017, 08:37 AM
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With a "low" top speed and a sluggish pick up I wouldn't suspect gearing just yet

1992 190E 1.8 <=>2.0 201.018 => Daily driver

1981 300D (non turbo) 123.130 => Project car - stripped to the bone

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post #4 of 10 (permalink) Old 04-28-2017, 08:51 AM
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the acceleration should not be affected at al, since in theory you have an engine with much more power.
besides in fifth gear, where it might be slower than fourth paired to the old engine (witch then was the top gear)

by "top speed is affected" what do you mean? its worse with the new engine compared to the old? or compared to the old car that engine was in? (the w201 has lower wind-resistance, and is lighter, so it would not be strange if the car feels a tad slower now)

Here you have a list of different differentials/finaldrives and what fits the w123
differentials, gear-ratios and compatibility | Mercedes-Benz turbo

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post #5 of 10 (permalink) Old 04-28-2017, 01:01 PM
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What I should have made clearer is that (generally speaking for W123s in particular) with gearing you can either be a super hero at the traffic lights but go deaf due to screaming engines at motorway speeds or have a much quieter life at motorway speeds but watch cyclists / mobility scooters burn you off at the traffic lights...

...the problem described in this thread sounds to me to be more related to poor engine performance than gearing (at the moment - based on what's been said so far)

1992 190E 1.8 <=>2.0 201.018 => Daily driver

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post #6 of 10 (permalink) Old 05-02-2017, 01:25 AM
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Quote:
Originally Posted by swampmonkey View Post
the m102 in the s123 that came with a fivespeed (i had the 2.0 liter carburator in one car) had a finaldrive ratio of 3.58, and that would make the car a bit more sluggish than your current 3.69.
The M102 2.0lt carb had a 3.69 diff, same as the M115 2.0lt, M115 2.3lt, M123 2.5lt I6, and 240D

The M102 2.3lt fuel injection engine sometimes had a 3.69, sometimes a 3.58 diff. The 280E sometimes had a 3.58, sometimes a 3.46 diff.

Here in South Africa we typically had the 2.3lt M102 with a 3.69 diff and 4-spd manual, or 3.58 diff and automatic, to compensate for the high and dry climate.

Quote:
Originally Posted by MR_BENZO View Post
Hii Geeks,
I had recently swap my M115 engine to M102 985 engine with 5 speed manual trans, I didn't swap my differential and still using my old one for the M115 engine, I can feel that the acceleration is not that good and the car top speed also I think is affected 170 KMH which I think that the differential is the main cause so I need you confirmation on this, also I need you help to know what is teh best differential ratio to have as per my knowledge it is 3.69 is this correct

Regards,
The M102 was a major improvement over the M115 in terms of efficiency and fuel economy, but was never going to have a massive performance increase. MB intended for the six-cylinders to be the more sporty variants. The performance you mention seems to be typical and correct.




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post #7 of 10 (permalink) Old 05-02-2017, 01:52 AM Thread Starter
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Hello all,
I don't know my current differential ratio that I use "For the M115", I believe that the ma102 2.3 differential ratio should be 3.69 I will check my current one and will update.
If it is not the differential that is affecting my top speed, what else I should suspect and how to test.

Regards,
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post #8 of 10 (permalink) Old 05-02-2017, 02:04 AM
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Quote:
Originally Posted by PlaneCrazy View Post
The M102 2.0lt carb had a 3.69 diff, same as the M115 2.0lt, M115 2.3lt, M123 2.5lt I6, and 240D

The M102 2.3lt fuel injection engine sometimes had a 3.69, sometimes a 3.58 diff. The 280E sometimes had a 3.58, sometimes a 3.46 diff.

Here in South Africa we typically had the 2.3lt M102 with a 3.69 diff and 4-spd manual, or 3.58 diff and automatic, to compensate for the high and dry climate.



The M102 was a major improvement over the M115 in terms of efficiency and fuel economy, but was never going to have a massive performance increase. MB intended for the six-cylinders to be the more sporty variants. The performance you mention seems to be typical and correct.
hmm, i looked at a 200gasser carb with automatic, and it had a 3.58, and im atleast 80% certain that was the same ratio i had on the 200T s123 fivespeed i have. (before it got the 2.47LSD it has now) might be a regional difference, in sweden the 240TD came only with 15" steel, and not 14" for example.

anyhow, the difference between a 3.58 and a 3.69 is not much, so little that i would not consider a swap "worth it"

@TS, i would look at the engine, as good as you can, that it performs as it should, are your exhaust in good condition, no catalysator that is clogged? is the timing correct, fuelpressure, have you had the exhaust "tested" that Lambda/HC etc values are correct?

the 2.3 is a rev-happy engine, down low torque isnt that much due to ratio bore/stroke, but at 3500rpm somewhere it should be happier,

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post #9 of 10 (permalink) Old 05-02-2017, 02:36 AM Thread Starter
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Hiiii, Regarding the exhaust I have a brand new one installed with the engine, I dont also have a lambada sensor, fuel pump also is a brand new bosch pump so I think the fuel pressure is ok, regarding the timing can anyone tell me detailed steps on how to check.

Regards,
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post #10 of 10 (permalink) Old 05-02-2017, 02:55 AM
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Quote:
Originally Posted by swampmonkey View Post
hmm, i looked at a 200gasser carb with automatic, and it had a 3.58, and im atleast 80% certain that was the same ratio i had on the 200T s123 fivespeed i have. (before it got the 2.47LSD it has now) might be a regional difference, in sweden the 240TD came only with 15" steel, and not 14" for example.
It may well be regional. Here in South Africa I've never come across a M102 2.0lt with anything but 3.69.

Quote:
Originally Posted by swampmonkey View Post
anyhow, the difference between a 3.58 and a 3.69 is not much, so little that i would not consider a swap "worth it"
The car that donated its engine to Donkey was originally a 280E 4-spd manual, with a 3.58 diff (The previous owner did the conversion from M110 to OM617). I drove that car a good long while in order to decide which of the two I would keep and which I would sell. Then I decided to keep Donkey. I installed the OM617 engine (still with a 4-speed manual) in Donkey, keeping her 3.69 diff and speedo, becuase I also didn't consider the 3% loss of speed worth the trouble.

It made a difference.

3% less top speed also meant 3% more revs per km travelled. It meant 3% more torque to the wheels. Donkey was much livelier with the same 300D engine than the donor car was. Their specification levels were the same, so their final masses were similar. Surprisingly, the fuel consumption wasn't affected much between the two. (Of course, the fuel consumption was greatly affected on Donkey by the conversion from OM616 to OM617. But I've mentioned that enough times elsewhere on this forum.)




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