Took my 97 S420 in for 90,000 mile service and have noticed a whining sound coming from the rear for quite some time. At first I thought it sound more like bad tires. The Mercedes Service Rep informed me it was my rear diff. He told me, "I would not worry about." I consulted a friend, who I think has some experience in mechanics and he also told me the same, however, he also informed me about Hypoid Gear Oil, it will make a difference. Is this an expesive repair or replace? Although the car still rides very nice, that whining sound really annoys me! Help!!

Thanks

wlk1997

First, "hypoid" refers to the kind of gear, not a kind of oil. It this case, it would be the pinion & ring gears in the differential. Hypoid gear oil is oil formulated for use with hypoid gears. It has an additive package that can handle the extreme pressure that these gears can create.

Chances are you already have hypoid gear oil installed in your diff (see above) . Anyway, as a first step to solving your problem it would probably be advisable to change the oil in the differential. You may be running a bit low, or it may just be time to do it. Alldata specifies 85W-90,90 GL-5(Gear Oil, API Service GL-5). If it quiets down, then the problem is solved (for a while at least). Ultimately though, the whining is caused by a misalignment of the gear teeth. This can be caused by wear or bad assembly. Either way, the the only way to permanently fix it will be to rebuild or replace the differential.

My previous car (SLK320) had a slight whine in the differential for 50,000+ miles and never caused any problems. I found it was a lot cheaper to just turn up the stereo a bit.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Bob, thanks for the info! According to the dealer, they did change gear oil and he did inform me that it might quiet a bit or not. It did not. Any ball park figure of how much it would cost to rebuild?

I would look into a MB rebuilt, from what I have been told MB uses a sophisticated method of setting up the gears. its not like your fathers chevrolet where you could set it by the pattern on the ring and pinion. Or live with it, it cant be that bad.

I can't speak for the differentials, but I recently installed an M-B rebuilt transmission and I consider it money well spent. In addition to getting that "factory quality", their rebuilt stuff comes with a two year warranty as well.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Any good leads on a rebuilt S420 1997 Rear Differential?

Click the "Buy Parts" link above and ask Phil to give you a quote!

He is gracious enough to provide this website free of charge, so give him the opportunity to do business with you.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

I decided to go the MB rebuilt route on my transmission, thru the dealer. I did talk to independent shops but no one would give more than a 90 day warranty, its insurance especially on the road.
The question is who will install it and warranty it, its not like the good old days when you would yank the axle shafts and replace the differential.