Hi All new to this forum but not Pelican. Just picked up a 71 220 with a manual 4 speed transmission. It revs too high for my taste on the freeway here in SoCal so considering swapping the diff with one that has a taller ratio. According to my info I have a 3.90 to 1 ratio. I realize I will lose some low end acceleration but thats OK. I used to have a 240d so I can live with slow.

My question is what year and model Mercedes should I be looking for that the diff will fit or hopefully be a be a direct bolt in to mine?

Obligatory first post picture attached. THX!

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I'm going to guess that a 6-cylinder c107 or w123 would be ideal since I believe they use the same rear subframe and should bolt right in.


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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,

A:

All 4, 5, & 6 cyl. cars from 1968 thru 1985 use the same basic diff ("small center section" in MB speak). Ratios range from 4.36 to 2.88. '75-76 W114/115/116 cars will have 3.69. Taller ratios appeared in later cars.

Thanks for the replies. For got to mention that this car is a gas engine and not a diesel so any opinions on how "tall" I can go are appreciated. I realize we are getting into a subjective area. I'm in San Diego, not Nebraska so we have a few hills but nothing huge.

Also, are the diffs marked externally to ID or do Ihave to open up an count ring gear teeth? 123s were pretty plentiful in the junkyards a few years back.

Given that you have a manual box (internal ratios> 3.9, 2.3, 1.4, 1:1), a final drive ratio of ~3.45 might be manageable.

The center section main cases are stamped with the ratio. It is on the lower rear corners of the machined rear surface of the case, adjacent to the rear cover. Clean off yours to see what it is.

Thanks for the reply.

I have to find my notes and math formulas from when I did this on a car years ago with the same 1:1 final drive trans ratio. Thinking from memory speculates that going from my 3:90 to a 3:45 will lower my rpms by about 400 to 500 at 70 mph.