well, i changed my diff. oil, but the noises continues. how can i tell if it's the inner or outer bearing? i've never messed with wheel bearings before...anything i should know before i delve into this?

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1985 300D Turbo "Eunis"

I think you are right My rotors are new (replaced all of them over the past 8 months) and pads too, but the parking brake shoes on the right rear were veeery corroded when I had the rotor off, might be because they don't work on that side....I only have functioning parking brake on my rear left wheel, thats it. I think I will be having that fixed soon.......probably a good idea, I'll order some parts and bring it in when its a little warmer out/I have time to leave it there a day. The squeaking has been getting less and less lately now....so I am assuming the new rotors are "worn in" to the position of the very corroded parking brake shoes....the old rotors had grooves about .2" or so on the insides where the shoes rub, the new one probably had to wear in a little to fit the shoe's position, as I am assuming they are seized in that spot....oddly enough the left ones looked/work fine.....

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Refer to post #12 Brian Carlton and post #15 whunter.

i'm officially stumped. i jacked her up and spun the rear wheels manually, and both made a scraping noise when i turned them. it sounds as if the brake pads are slightly touching the rotors. the car rolled backwards when i let it down, until i put the parking brake on, so i know that works. any ideas?

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1985 300D Turbo "Eunis"

Its normal for the pads to rest lightly on the rotors and make a slight scraping sound. The front wheels can be spun nicely to check for too much drag, for example if the caliper pistons aren't releasing due to build up in the bore. The rears can't be spun likewise because of the gearing in the diff.
I have been trying to identify a grinding noise that increases with speed, I believe its the inner bearings, darn it! that isn't something I want to deal with because changing them is not an easy job
If you suspect your pads are dragging, just drive a few miles then slow down and come to rest without using the brakes. Feel the rotors, they should not be hot. Warm maybe but not hot if you haven't used the brakes to stop the car for a while. It takes a back country environment almost to do this but is a good method of checking for caliper problems like that.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Are we still troubleshooting the bearing noise while driving, or is this something else?

If you can spin the wheels manually, there are no brake dragging issues. The "scraping noise" is just the pads sitting on the rotors. It's normal.

Just because you changed the oil in the differential doesn't mean the differential whine will go away. It may be reduced a bit but likely will not go away. Once the gears wear to a state that causes this kind of whine, its not a matter of lubrication to get it to stop.

To me it just seems to be a design issue. Many other vehicles with high mileage never develop a differential whine. If the specified change intervals are followed (30K miles with dino gear oil) then that may help prevent the gears from wearing to the point of whine.

You could replace with a used differential but the chances are pretty good the replacement will whine too. And you don't want to price a new differential from the dealer.....

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

rear rotors and inspect the parking brake for damage.
It may be full of rust.

how long will the diff i have now last? the whine is pretty loud. i put mobil 1 synthetic in it, if that makes a difference in its longevity. also, it didn't get any quieter after i changed the diff. oil.

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1985 300D Turbo "Eunis"

at this point, i'm not sure if it's wheel bearings causing my problem. i plan on taking the calipers off, putting the tire back on, and spinning the wheel by hand. hopefully that will eliminate 1 or more possibilities.

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1985 300D Turbo "Eunis"

There is one differential wear mode that you can test for with no disassembly. With the transmission in neutral reach under the car and turn the driveshaft back and forth to observe the drive train slop. If the driveshaft turns very much back and forth with the car sitting still then you may have a badly worn differential. This is also obvious in those cases where you put the car in park and it will still creep forward or backward a good distance before settling against the transmission stop. Same likely reason - differential wear.

If its not doing this then the next likely wear point is probably the bearings inside. These really should last a long time with proper lubrication, but I suppose there are always exceptions.

Personally, I think if you have little drivetrain slop as described above, you should drive the car until something else under there goes wrong, like the axle shaft boots or something. Then consider a differential replacement as part of that repair.

400K miles is nothing for a well-maintained differential - especially if the transmission is shifting properly (not too hard) and the driver is moderate.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Have you checked the wheel wells for objects (such as cats, small dogs, or moles

i took my car in for my mechanic to take a look/listen. he said it's definitely differential. the car does move back a lot when i put it in park, too. how hard is it to replace the diff?

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1985 300D Turbo "Eunis"

In the shop on a hoist = 0.5 - 1.5 hour if all fasteners are corroded.

I just had this problem. I had a bad wheel bearing in the left rear and I have a noisy differential ever since I put in a new differential mount, rear shocks and springs.

One fix caused another problem.

Could be your differential. Pump out the fluid and do what the other guys said with the synthetic. My pinion bearing is giving my noise. Mine starts whining at 40mph and increases with speed not RPM.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup