Noob rear diff question
 

So have this 81 240d, what year range can I look at for different gear ratios that are "bolt in"

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R/C 107 - '73-'85 all w/ 6 cyl engines
W114/115 - all
W116 - all w/ 5 & 6 cyl engines
W123 - all
W126 - '81-'85 all w/ 5 & 6 cyl engines

Supposedly ANY 1985 and older diff from a W116, W123 and W126 will fit.

Gen 2 W126 diff will NOT fit.

Sourced from here.
https://mbturbo.com/gear-ratios/

V8 diffs wont fit directly as the yoke is bigger and needs to be swapped over. Also the washer behind.

larger rear tires will help fuel mileage

Whilst the some of the specified differentials will fit in terms of "fill the hole" not all of them are going to be especially fantastic when used in a 240D

The final drive ratio is important - especially if you have an automatic transmission and if you wish to have an accurate speedometer reading.

Speedometer gearing is matched to final drive ratio - shifting points more or less "matched" to expected final drive ratio.

If you tell us your objective we can advise on ratio decisions for your needs.

Awesome thank you!!

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Have this 81 240d 4spd, but has a 300TD swap, has the 3.69 rear now going for the 2.88 for better highway speed and possible mileage

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Also, will a VIN tell me the rear ratio if I xA t get to it to physically see it

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VIN

https://uploads.tapatalk-cdn.com/201...fa3c2fcbb4.jpg

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The serial number will tell you what it left the factory with. Look on the flat part of the diff where the rear cover bolts on and it is stamped there. You're on the right track with the 288. Unless you live in san fransisco then I go a bit lower.

Yup knew about the stamp just can't get to it where it is sitting ill see if I can find a VIN decoder to tell me..

Thank you!

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Well found a few decoders but nothing on the VIN tells the rear ratio...so I guess it will be that I have to have some help getting this thing up where we can get underneath it to look for the stamp.....

The VIN says US spec ‘83 300D. I think that means 3.07. 2.88 might be MY ‘85 only.

Sixto
98 E320s sedan and wagon
02 C320 wagon