Rear end failing - what are my options?
 

Hi kids! I have a 1980 300SD with 451,000 miles and going strong, but the rear end is getting loud. Anything tricky about a swap? Special tools?
I have a dead 1978 280SE W116 six-cylinder that I could use as a transplant, compatible?
How do the gear ratios compare?
Is there a tag on the boxes indicating ratio?
Do we have a table somewhere here listing ratios?
I would love to have limited slip, but is that especially hard to find in the ratio I need?
Any clues would be appreciated, thanks!
David in rural Oregon

The lower passenger side of the diff should be stamped with the ratio.
Your SD should have a 3.07
If the diff isn't the same you can swap the speedo with the diff...

I haven't seen this answered for our cars however other vehicles I've owned have had a mechanical drive gear that matched the rear end gear ratio. It was easy to swap the drive gear to keep the speedo correct.

The 85SD has an electric speedo. I haven't looked for the pickup.

Right rear end ratio should be a junkyard item. Rear ends are not a high failure rate on these cars.

No variable ratio speedometer drives for these buggies.

(Do we have a table somewhere here listing ratios?)

Diff info?

Sooo... A 3.69... Yeah, that is going to be a problem... Your top speed is going to be around 70 and it's going to be LOUD at that speed... But you'll get there quick...