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Old 12-15-2009, 08:39 PM
Oldbeaver's Avatar
MBZ 1993 turbo diesel
Join Date: Jul 2007
Location: Chile
Posts: 52
Need a 3.92 differential for a W124 diesel.

Hello all!

I am looking for a 3.92 differential for my 300E 1989. At present, I have a 3.46 differential, but I think it is too long.

What MB models carried a 3.92 differential?

Originaly, my car had a 3.07 differential. When I swapped the gas engine for a diesel, it became far too long. Then I discovered a used diff in a dismantling yard with a 3.46 ratio. The donor car was a 201 (W201 I suppose), probably a C280?

It looked very similar bolt to bolt, and after interchanging the palliers, it fitted in place. The car performance improved quite a lot.

However, the engine is revving too slow even now. I can drive for the city at 45 miles/h at 1500 rpm. Maximum speed I have attained so far (donīt like to run too much) is 105 miles at 3500 rpm, while max performance of the car is at 4500 rpm. I rarely drive the car at more than 2000 rpm. Only in slopes or over 65 miles/h.

The engine donor car had a final ratio of 4.09.

I know there are several experienced guys in the Forum, that may be able to help. Do you people know which Mercedes models used 3.92 final ratio differential, which is compatible with a normal W124 differential? This would ease the search for the differential.

I also have a 3.07 diff just in case.

Thank you very much in advance,

Old Beaver

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Old 12-15-2009, 11:03 PM
awsrock's Avatar
Registered User
Join Date: May 2008
Location: Tinley Park, IL
Posts: 633
Wow, a 3.92??? I don't know if they make any of those. That 3.46 must be from a manual model. The highest ratio from a 124 that I have heard of was a 3.27 off of the wagons (I could be wrong though)

Anyway, the automatic turbo w124 diesels came with 2.65 diffs, so going up to a 3.92 sounds kind of extreme to me. The only benefit I can think of that giving you is really quick acceleration off the line.

Why do you want to run it at higher rpms? There should be sufficient power the way you are running it now. Heck, some of us 124 and 126 guys lust for the 2.47 or super low 2.24 for better highway cruising.

However, I guess it really depends on what gear ratios your trans has, and what kind of engine you are running. Is it the om603? Are you manual or automatic? Something sounds weird about going 105 and only being at 3500 rpm with a 3.46, since the 2.65 maxes out around 125 or so.

Also, if you are in Chile, I suppose there could be a lot more parts available there than what we are used to here.
1987 300SDL s200g, Herlevi pump, Elbe manifold, 2.47 LSD - 203k
Past: 1987 300D - 264k

Last edited by awsrock; 12-15-2009 at 11:10 PM.
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Old 01-08-2010, 02:49 PM
JimFreeh's Avatar
Benz addict
Join Date: Mar 2007
Location: Hampton Roads, Virginia
Posts: 3,354
3.92 was installed in the w115 220D. Some had 4.07 as well.

Your 86 and up W126 has a different diff mounting than the earlier w126, which interchanged with the W123 and W115/W114 pumpkins.

Also, the V-8 cars had a larger diff, 1.3L vs 1.0L capacity.

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Old 01-08-2010, 03:53 PM
aaa aaa is offline
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Join Date: Nov 2008
Posts: 1,075
The mounting is completely different on 86+, so I would think that the older diffs are out of the question.

But yeah, something doesn't sound right. For example, if the rpms are too low why don't you just downshift? I didn't hear anything about wanting off the line acceleration, so if you ignore that you can get the extra performance that way.

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