Rear diff whine after fluids swap
 

Put some RedLine fluid in the diff of our "new" 245K mile E300D. Now it has a pretty good "whine".

Backlash is the typical put it in drive and clunk goes the rear end with this 95.

Dont beleive the 95 called for synth gear oil. Thinking of swapping back dino 90w but...first

does this whine indicate too much wear, or is is simply a function of the lighter synth fluid and a loosely set up ring/pinion? Meaning, is it critical I put heavier lube back in? Or can I let it "sing" thru the colder winter?

I've had the clunk before, in almost all the 300s I've owned, but never such whine from the R&P.

If it made the differential noisier and it does not call for synthetic probably should change it back to dino. If you change it back to dino please let us know if the noise stops.

About the clunk, what is the condition of the transmission mount, differential mount bushings, flex discs and center support?

IIRC certain versions of the 95 called for a special fluid. Ones with ASD, perhaps?

I have the same whine in my 85' 300d. I've had the issue since I started driving it. I topped off the fluid yesterday and that didn't help. Any suggestions?

Use a heavier grade oil. 75w-140 synthetic should be perfect. It's a shame the Redline makes it whine. That's expensive stuff and the whine would drive me crazy. My diff is starting to whine a bit when I hit the "sweet spot" of the throttle. I might try an XXw-110 grade oil first and see if that makes it quiet, if not I'll bump all the way to 140.

Even though its 50F here in Buffalo right now, most of us NEVER use the 90-140W. I'll be doing a transmission fluid and filter change this weekend. At the same time , I'll drop the RL synth ( and save it!) and refill with dino 80-90w, which is what I believe the car calls for. Will advise on result.

Unsure of how to know whether the car has 'ASR'. Is that electronic limited slip?>


I dont like the noise. I can almost count the ring gear teeth at a crawl. Gives me a pucker factor. I've grenaded rear ends before, but never with 125 HP and an automatic trans! :)


Jack, the whine ( well at least the whine in our car) is typically from excessive backlash. Truly any ring/pinion setup properly with the required 008- .010 backlash should be relatively quiet regardless of fluid weight. ( although I;ve installed Richmond gearsets before that wont quit whining with the right backlash and contact pattern. )

I've got M1 synthetic gear lube in my '95 E300 with ASD, no whine. The (replacement) diff was catching initially during sharp turns, with regular old dino lube, after my indie installed it. I added the small bottle of MB special additive for LSD differentials with the M1, and no more catching.

I don't think any additive will help here.

I would try and source some 85w90 Liqui Moly 235.0 gear oil, I believe that's the original spec for non-ASD cars and it's what I have in mine. I found it at Napa (I think) locally for around $9 a bottle. Sometimes it's best to keep with "approved" MB fluids, at least that's my thinking, even though many use non-approved stuff with no issues.

Well that'll happen if you drain the saw dust!

What weight oil did you use? If you used the proper weight in synthetic it shouldn't be "lighter" at all.

Indeed Paul as swapping back to 80-90 dino GL5 made no difference. Still "whiney". Oil did not look like oil with less than 10K on it.

Maybe next time I'll try the 85w90 Liqui Moly 235.0 gear oil.

Likely too much backlash, as I suspected. Dont know why I did not notice it until after the fluid change. My sons car, but I test drove it initially, ( bought at 233K) and afterwards while doing service items.

Thanks everyone for responding.

Synthetic versus conventional makes no difference.

You'll need to go heavier. Try a 75w-110 if you're anxious about going to a 140. It's a good intermediate oil. A worn out diff is going to be noisy. Thicker oil helps cushion the teeth and helps dampen the noise.

Yup. But not before winter. Will have to put up with a bit of noise.

As you wish.

Whenever you see a newer Fotd truck driving around, know that they are filled with 75W-140 gear oil.

Reference this chart to debunk the "thick gear oil" myth.

Here is my 2 cent experience and I've stated this many times before.

When you switch from conventional oil to a synthetic oil on a high mileage diff, you have to open it up first and clean out all the old oil and debris. The synthetic was very good detergents that it dislodges any debris and suspends it in the oil.
Unfortunately, there is no differential filter to filter this oil. So circulates and destroys the wearing surfaces which causes the whine.
If you can not open the cover, stick with conventional oil. Preferably, the recommended 85w90.

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