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Old 07-10-2003, 05:22 PM
Obaid Rehman
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123 Differential Question

I need to replace differential of of my 1977 240-D 123 series because of the noise. The ones that are available with the old parts dealers have differentials of the following "ratio" and I am not sure which one would be the best. Help would be highly appreciated.

(a) 3.69 (b) 3.92 and (c) 3.48

I am told by some one that if the ratio is higher (eg 3.92) it is better then when the ratio is lower (eg 3.48). Please comment on this too.

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Old 07-10-2003, 05:41 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
The W123.123(240D) chassis uses a 3.69/1 ratio.
The 3.92/1 ratio was used in 1969 to 1975 220D's
The 3.46/1 ratio was used in the 1977-1981 300D non-turbo.
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Old 07-10-2003, 06:00 PM
Obaid Rehman
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Thanks MB Doc.
I am also told that there is another differential off a petrol MB with 49 grooves ( ratio not known to me). If I install it in my non-turbo 240-D 123 series, will it be any good in it? Will there be any improvement in acceleration?

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Old 07-11-2003, 04:15 PM
Obaid Rehman
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Need some more help please!
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Old 07-11-2003, 07:35 PM
tvpierce's Avatar
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Join Date: Feb 2002
Location: Portland, ME
Posts: 612
A higher number will give you higher revs (and consequently better acceleration). The drawback is that your engine will rev higher at cruising speed. So you're fuel economy will decrease, and your engine will be louder at a given speed. Additionally, your speedometer will be inaccurate if you change from your original gearing.

In the case of a differential with a gear ration of 3.69/1 ("3.69 to 1"), what the numbers are actually telling you is that the wheels will turn 3.69 revolutions for every 1 revolution that the driveshaft turns. So a differential with a "higher" number is said to be geared "lower".

Hope that helps.

Jeff Pierce
Jeff Pierce

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