Some of you may have read my recent thread regarding a true cold air intake for my 350SLC Improvements to M116 in early 107 (true cold air intake) where I mentioned I am planning to use this car for a little motor sport, hence my search for performance improvements.

I recall hearing that the 3-speed, torque converter transmission (722.0?) in my car is virtually the same as the 4-speed unit (722.1?) fitted to the six cylinder (eg. 280E, 280SE/L, 280SL/C) W107, 116 & 123 and various diesel models of that era. I have heard that the similarity extends to the 3-speed actually having 4 ratios, with first not being accessible. I know the ratios of the 3-speed correspond with 2nd, 3rd and 4th of the 4-speed which makes for a very tall first gear in the 3-speed. My 350SLC can do a 0 to 60mph (almost 0 to 100km/h) sprint entirely in first gear!

Is it possible to modify the 3-speed (eg. valve body mods) to allow the true first gear to be accessible? Alternatively, can the 4-speed be bolted up to and used successfully with the V8 engine (iron block M116 in my case)? The addition of a lower first gear together with the torque converter would really launch this car well. It would possibly even allow the use of a taller diff than the present 3.46 to give lower cruising engine speeds with better fuel economy, yet still with good acceleration from standstill.

I had considered the possibility of trying to source the 4-speed manual transmission that was available for the 350 and 3.5 models, however they are rare in Australia and I have also heard they are very costly to repair. On the other hand, the auto transmissions of the 1970s have a very good reputation, better than either that of the fluid-coupled autos of the 1960s or the autos of the 1980s and 1990s.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.