Different differential gear ratios. Probably a 3.92 in the W115 and a 3.58 in the W123. Apx 9% difference in final drive output. It would definitely be noticeable.

https://www.benzworld.org/forums/w123-e-ce-d-cd-td/1611616-rear-differential-interchange.html

" Years, Model, Engine, Differential Ratio, Differential Case Size, Ring Gear Size

R107
1st Generation mounting
1972-1980, 350 SL/SLC, M116, 3.46, 1.1 Liter, 185mm
1973-1980, 450 SL/SLC, M117, 2.65 / 3.06, 1.3 Liter, 210mm
1981-1985, 380 SL, M116, 2.47, 1.3 Liter, 210mm
1981-1982, 380SLC, M116, 2.47, 1.3 Liter , 210mm

W114
1968-1976, 230, M180, 3.69 / 3.92, 1.1 Liter, 185mm
1968-1972, 250, M114, 3.69 / 3.92, 1.1 Liter, 185mm
1972-1976, 250, M130, 3.69 / 3.92, 1.1 Liter, 185mm
1969-1976, 250C/CE, M130, 3.69 / 3.92, 1.1 Liter, 185mm
1972-1976, 280/E, M110, 3.69 / 3.92, 1.1 Liter, 185mm
1972-1976, 280C/CE, M110, 3.69 / 3.92, 1.1 Liter, 185mm

W115
1968–1976, 200, M121, 3.92 / 4.08, 1.1 Liter, 185mm
1968–1976, 200D, OM615, 3.92, 1.1 Liter, 185mm
1968–1973, 220, M115, 3.92 / 4.08, 1.1 Liter, 185mm
1968–1976, 220D, OM615.941, 3.92, 1.1 Liter, 185mm
1973–1976, 230.4, M115, 3.69, 1.1 Liter, 185mm
1973–1976, 240D, OM616.916, 3.69, 1.1 Liter, 185mm
1974–1976, 240D 3.0/300D, OM617.910, 3.46, 1.1 Liter, 185mm

W116
1973–1980, 280S, M110, 3.69, 1.1 Liter, 185mm
1973–1980, 280SE, M110, 3.69, 1.1 Liter, 185mm
1974–1980, 280SEL, M110, 3.69, 1.1 Liter, 185mm
1973–1980, 350SE, M116, 3.46, 1.1 Liter, 185mm
1973–1980, 350SEL, M116, 3.46, 1.1 Liter, 185mm
1973–1980, 450SE, M117, 3.06 / 3.07, 1.3 Liter, 210mm
1973–1980, 450SEL, M117, 2.65 / 3.06 / 3.07, 1.3 Liter, 210mm
1975–1980, 450SEL 6.9, M100, 2.65 LSD, 1.3 Liter, 210mm
1978–1980, 300SD, OM617.950, 3.07, 1.1 Liter, 185mm

W123
1977–1978, 230, M115, 3.69, 1.1 Liter, 185mm
1977–1983, 240D, OM616.912, 3.69, 1.1 Liter, 185mm
1977–1981, 280E, M110, 3.58, 1.1 Liter, 185mm
1978–1981, 280CE, M110, 3.58, 1.1 Liter, 185mm
1977–1981, 300D, OM617.912, 3.46, 1.1 Liter, 185mm
1978–1981, 300CD, OM617.912, 3.46, 1.1 Liter, 185mm
1979–1980, 300TD, OM617.912, 3.46, 1.1 Liter, 185mm
1981-1984, 300TD, OM617.952, 3.07, 1.1 Liter, 185mm
1982-1984, 300D, OM617.952, 3.07, 1.1 Liter, 185mm
1982–1984, 300CD, OM617.952, 3.07, 1.1 Liter, 185mm
1985, 300TD, OM617.952, 2.88, 1.1 Liter, 185mm
1985, 300D, OM617.952, 2.88, 1.1 Liter, 185mm
1985, 300CD, OM617.952, 2.88, 1.1 Liter, 185mm
Euro Spec
1981-1985, 300TD, OM617.912, 3.46, 1.1 Liter, 185mm
1982-1985, 300D, OM617.912, 3.46, 1.1 Liter, 185mm
1982–1985, 300CD, OM617.912, 3.46, 1.1 Liter, 185mm
1978–1985, 240TD, OM616.912, 3.69, 1.1 Liter, 185mm
1978–1985, 280TE, M110, 3.58, 1.1 Liter, 185mm

W126
1st Generation
1981-1984, 300 SD, OM617.951 3.0L I5, 3.07, 1.1 Liter, 185mm
1985, 300 SD, OM617.951 3.0L I5, 2.88, 1.1 Liter, 185mm
1984-1985, 380 SE, M116.963 3.8L V8, 2.47, 1.3 Liter, 210mm
1981-1983, 380 SEL, M116.963 3.8L V8, 2.47, 1.3 Liter, 210mm
1982-1983, 380 SEC, M116.963 3.8L V8, 2.47, 1.3 Liter, 210mm
1984-1985, 500 SE, M117.963 5.0L V8, 2.47, 1.3 Liter, 210mm
1984-1985, 500 SEL, M117.963 5.0L V8, 2.47, 1.3 Liter, 210mm
1984-1985, 500 SEC, M117.963 5.0L V8, 2.47 /(Euro) 2.24 LSD/(Euro) 2.47 LSD, 1.3 Liter, 210mm "

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