Swapping for 300SE Differential

[tomsmb]

I heard a rumor that a diff from a 300SE was a simple swap which gave a lower numerical ratio thus  lowering the rpm at highway speeds.  Has anyone on the forum done this?
Was it an easy swap? 
How do you determine that the diff you are swapping in has a lower numerical ratio? 
What does it do to acceleration in the lower gears? 
Is the 300SE axle  the same "Swing axle" configuration? 
Are there really any benefits from doing this?

[Garry]

Tom,

There are pages and pages of information on doing this and what effect it has, how to tell what ratio the rear differential is etc etc.
Do a search under "rear axle swap" or try just rear axle.

[ja17]

Hello,

As Gary has indicated, there is a lot of detailed information on this conversion already on this site.   300SEs and 300 SELs have air suspension and these will not work on a W113.

You need a diff from a Mercedes W108 sedan with a V-8 engine 1970-1972, models 350SE, SEL (3.5 V-8 engine) or Mercedes W108 sedans 280 SE, SEL (4.5  V-8 engine).

Quite  a few are still around but are dissapearing fast.

[wbain]

There was one 300SE model that would work but these are rare. It's the 300SEb which is a W108 with the M189 alloy engine and steel springs. Personally I would not use that car because it could be easily restored. Mr. JA17 has one and I lust after it.

Find 280SE/SEL 4.5 and swap rear ends.

Oh and Joe, thanks for the info on the flywheels.

[ja17]

Hello Warren,

You are correct, a rare  300SE with springs was produced (european delivery only) 2,700 made total.  However, being a six cylinder the rear gear ratio is not the desirable upgrade (3.92 or 3.69 ratios).   The V-8 axels, as you know, were 3.27 and 3.46 ratios.

[tomsmb]

Thanks everyone.   In reviewing all the stuff on the forum I learned early on that the swap was effective for manual transmission cars and mine is automatic.  So much for that.

I've lived with the high rpms at highway speed for 11 years so I guess I can continue. 

[ja17]

Hello Tomsmb,

On the contrary, most of these conversions have been on automatic cars!

[julianmaba]

Tomsmb - after your reviewing the forum on ratio changes, did you see if folks who have tried this (move to a higher ratio diff i.e. 4.5L) were happy with the higher final drive ratio and, specifically any negative reactions to the change in acceleration and auto shift performance? Please let us know. With the higher ratio, one would have less acceleration, but maybe not enough worry about?

[tomsmb]

Everyone seemed to be happy with the lower rpm on the highway and none of the posts I read complained about sluggish acceleration.