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  #1  
Old 08-06-2016, 07:55 AM
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Rear Differential???

Hi Guys, first time user here.

Currently driving a 88,230E W124 Sedan 2.3 4 speed auto.

I'm looking to lower rev's a little on the highway.

Would adding the diff from a E300 diesel 4 speed auto achieve this.

230E diff= 3.27

300D diff= I believe high 2....

Thank you

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  #2  
Old 08-06-2016, 08:56 AM
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A few things to consider. If you drop the revs too much, the engine will be out of it's power band, lug and downshift giving you higher revs and lower top speed.

A quick way to change revs is to go to a larger OD tire. This is easy to do before you try a diff swap even if it is just for experimentation purposes. At this point you can calculate effective rear ratio to see if a diff swap is worth it.
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Old 08-06-2016, 09:17 AM
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Very good idea as the wheels are 15 on there and small tyres also,
Actually major gap between the fender and tyre.

Thanks I'll throw set of 16's on
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  #4  
Old 08-06-2016, 12:56 PM
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Rim size doesn't mater, outside diameter does.

It is possible to get 16" that has the same OD as your current 15" so make sure whatever 16 you try, the outside diameter is larger.
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  #5  
Old 08-07-2016, 06:46 AM
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I just measured the 16's on my wife's Merc and yes there the same
Overall diameter of the 15's.

So maybe a 16 with a taller tyre..
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  #6  
Old 08-07-2016, 07:22 AM
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Or a taller tire for a 15 wheel. It all depends on what tires / wheels you can easily come up with for testing.
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  #7  
Old 08-07-2016, 10:32 AM
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The diff may interchange with many other benz chassis. But be aware that there are several differences to consider, even within the same model. Is it an antslip rear? Does the car have anti lock brakes? What is the diameter of the input and output flanges?. You need to research these factors, or you will get half way through the conversion and face an unsurmountable problem. I really dont like tire swaps, its a crude approach. Tire swaps are likely to have profound effects on handling, load and traction. What usually happens with tires is that someone goes out and drops $2k on tires and rims, and reports amazing results. Nobody admits that they wasted $2k.

The other consideration is that dropping the revs by either a diff swap or fiddling with tires will screw up your speedometer calibration. Unlike something like a GM or Ford car, its very hard to find corrective speedometer drive gears. Your alternative would be to find a matching speedometer head, or installing a conversion box.

The least problematic way to address this is to find a five speed overdrive transmission. That will allow you to select an appropriate gear for any circumstance. The speedometer would work as normal without modification.

Last edited by Mxfrank; 08-07-2016 at 10:44 AM.
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  #8  
Old 08-07-2016, 12:02 PM
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There are several on line calculators on the inter web that show what works best. On the whole "just a little bit" in rev reduction is actually more than changing tyres or wheels will do - but that really depends on what you are trying to achieve.

Use one of the calculators and you are less likely to be disappointed.

Failing that you can quite easily work it out for yourself if you enjoy playing about with numbers.

If you go down the route of changing tyres and wheels, there are other on line calculators that will give you an indication of whether you'll have to hack out bodywork to make your chosen solution fit or not!
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  #9  
Old 08-07-2016, 05:04 PM
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Quote:
Originally Posted by Mxfrank View Post
I really dont like tire swaps, its a crude approach. Tire swaps are likely to have profound effects on handling, load and traction. What usually happens with tires is that someone goes out and drops $2k on tires and rims, and reports amazing results. Nobody admits that they wasted $2k.

In the case of our original poster, a test tire swap can be done at much lower cost than the trans swap you suggest to see if the car can even handle lower revs at speed.

As an example, if his stock tire is 195 75 15 , moving to a 205 75 15 or 215 75 15 will hardly deteriorate handling but will drop revs enough to see if making a diff swap is worth it.

With a 2.3 engine, he may not be able to pull a taller tire ( gear ) and can swap back to standard tires in 1/2 hr Vs your very invasive transmission swap.

The only viable 5 speed auto was found on early 90's 300SL / 300SE and that might not even bolt up to his engine.

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