[W126 Coupe] 2.82 Rear Diff for 84 500SEC

[Gerry Van Zandt]

The 3.07 isn't all that bad in highway driving. At 80 MPH you're  
doing EXACTLY 3,500-3,550 RPM; at 65 it runs around 3,000 RPM.   
Redline for a 560 is what, 6K or a little higher -- there's plenty of  
headroom.  I drive my 89 560SEC from Portland up to Seattle quite  
regularly (a 2.5 hour trip) and it's really not a problem.

I'm still getting upwards of 15 MPG average per tankful.  The last  
tankful, all highway driving, was 17.59 MPG with the 3.07.  16 and 17  
MPG for tankfuls with all-freeway driving are not at all uncommon.

The benefit at low speeds and off the line far outweighs the engine  
running 700 RPM higher at 80 MPH, compared to a stock 2.47 car.

An 84 500SEC or a 380SEC is a direct bolt-up for a 3.07 from a sedan.  
The later cars (560s) require some slight mods -- the 3.07 gearset  
must be placed in a 560 pumpkin.  You do have to calibrate the speedo  
with an adjustment box.  Mine was about 10-12 MPH off.  This is easy  
to do and you can tuck it behind the instrument cluster back in the  
dash.

A 2.82 is a good compromise in terms of ratio, but it's not enough of  
a difference, IMHO, to warrant the time and cost of doing a  
replacement.  The 3.07 is a large jump and the results are dramatic.   
If one is doing the swap for better off the line quickness and such,  
I'd just go whole hog.  Those of us who have done the switch wouldn't  
go back.

Cheers,
Gerry



On Jul 20, 2007, at 9:15 AM, mbcoupes-request at mbcoupes.com wrote:


>

> As an aside, if you do a Lot of highway driving you might find the  

> 3.07

> from a 450 a bit Busy...granted it will feel Great off the line  

> though!

>

> Jonathan

>


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