my 83 300 cd has been making a whining/ grinding noise for a few months. I thought it may have been one of my cv joints because the dust boot was torn. I changed both today hoping for the noise to be gone and it made no difference. When i had the cover off the diff to remove the C clips, i saw no metal shavings and it had plenty of oil. It even has new oil now. The center carrier bearing is new as well. I am 99% sure it is the diff making the noise. I'm sure some of you will flip but i put the back of my car on jack stands, blocked the front tires and rigged my linkage to keep the car going around 30mph on the speedometer. That is where i notice it driving and also started hearing it up in the air. When under the rear, its very loud behind the diff when driving, it seems to get louder and change tone depending on load. There is a 1985 300sd at my local PNP that i was planning to get the 2.88 diff out of to swap. what do you think the noise is? will swapping the diff solve the problem? Thank you!

benzturbo's 300cd diff noise - YouTube

If you don't mind going through the trouble, remove the axles and run just the DS and differential. That removes any load from the differential and eliminates the axle and rear wheel bearings as a noise source. No need to put the cover on, the diff. can run dry with no load on it. Also, don't rule out the hanger bearing.

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'83 300D, 126K miles.

The sound for sure comes from the diff. I was thinking the same about wheel bearings. It seems to be making the most noise from where the drive shaft goes in to it. Pinion gear bearing?

Well the other rear end is an upgrade although you should get the head unit as well. The pair are also resellable remember. Then perhaps pull the bearing in your current rear end and examine it. You will have to do the pre load properly if you change the bearing.

I agree! I think i may get the 2.88!

Replaced my diff with the 2.88 from the PNP and it's great! Quiet and now a highway cruiser thank everyone for the input!

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83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect