Yeah 3.46 definitely needs overdrive. I drove my drift car(v8 3.69) to an event and it was a long 1+ hours at 65 and 3700 rpm.

I was looking at the w140 300se and s320 and they are both m104 powered and have a 3.69 early hydro trans car and 3.46 later electro. I'm curious if they are both 210mm gear diffs. Is the six or eight bolt side bearing cover a definitive 185 vs 210mm feature? It is on the old generation diagonal swing axle cars.

I read over the linked page about swapping gear sets from one to another and it sounds like a pretty serious job anyway. But so is modifying a subframe for non MB diff case. The asd with a small master cylinder to activate it is a cool idea I've seen too. Or an abs pump...

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When I said 210 I meant 210mm diff in my '95 S124, sorry about the confusion.

I believe all W140 cars have the 210mm diffs. It's pretty easy to tell them apart the 210mm is noticeably bigger in size compared to the 185mm and different shape.