W202 final drive ratio change (diff swap?)

[thephatmaster]

Hi there, Apologies if this a a double post - I posted earlier and it disappeared into thin air.

I think I'd like to do a diff swap and need some advice.

My W202 (facelift, manual, C200, with ASR) screams away at 3000+rpm at motorway speed (70mph). This is all very 1999 - when cars didn't have 6 speed manual, or 7-8 speed auto boxes.

I drive long distance mostly and wish to escape the 1990's gearing. I'd like to bring the rpm down to 2500 - 2700 at 70 as that's where max torque is (and presumably best brake specific fuel consumption values).

Presumably the C200, being lower power than some, was fitted with quite a short final drive ratio. I have seen anecdotal evidence that the manual C180 had 3.91 gearing, which is the shortest ratio if i am not mistaken?

Ive done some research and concluded:

1. The ratio fitted can be found stamped on the lower part of the final drive (diff) housing (I am yet to check what mine says, but will next time I'm under there);
2. There are various FD ratios avaiable across the W202 range ranging from 3.91/3.92 to 2.88;
3. The facelift W202 takes speed readings from the ABS sensor, so no speedo swap to worry about;
4. There were two sizes of propshaft coupling and two sizes of half shaft fitted accross the W202 range.

On (4) I was wondering how I can identify the various different sizes to ensure my propshaft and half-shafts are plug-and-play.

On (2), I'd like to know for buying-research purposes whether certain ratios were standard fitment on certain models - e.g. 2.88 and the like for big diesel engines, 3.91 for small petrol engines.

Any advice greatly appreciated.