Sorry guys - another 300SD funny noise post - PeachParts Mercedes-Benz Forum

300sdToronto · #1 08-19-2012, 05:36 PM

I hate to post another "funny noise" post but I have searched the forum and tried the obvious with no success. So I am turning to our collective wisdom for help.

The noise in question is an annoying, warbling whine. It gradually builds in volume and frequency (tone goes higher) and then ends abruptly, rather as though some component has come up to pressure or speed and is now "happy".

Further info:

- the noise seems to come from the CCU/gear shifter area. As it only happens while the vehicle is in motion I can't be more specific than that.
- the noise happens when I am accelerating between about 20 and 35mph and consistently goes away by the time I have reached 2000 rpm. It happens regardless of whether the rate of acceleration is gentle or hard.
- the noise also occurs if I lift off from the accelerator while the vehicle is in motion
- it's loud enough to be annoying but not loud enough to disrupt conversation, for example
- it happens intermittently and most consistently when the vehicle is cold
- car is operating fine apart from the noise.
- the noise has not happened in reverse (backing up)

What I've tried:

- Turn off CCU in case it's a blower motor issue. Nope.
- Replace seals on turbo air intake u-tube. Nope. Drove around the block with the u-tube off in case the new seals weren't seated properly. Nope. Did find a broken air cleaner mount in the process ...
- Popped hood and tried to replicate the noise with the car in park by revving through the right rpm ranges. Nope. I think this eliminates belts and belt tensioners, one of the usual suspects?
- Checked appearance of engine and transmission mounts and drive shaft flex disks. All looking OK. Did find and repaired a broken muffler hanger in the process.
- Checked transmission fluid level. OK.
- Checked differential oil level. OK.

I am now running out of ideas and if anyone has further ideas please post. As I said, the car starts, drives, shifts, corners and brakes just fine with no apparent change in behaviour apart from this damned intermittent whine at low rpm's/speed. The car is the 300SD in my signature - a 1983 with 165,000 kms.

ROLLGUY · #2 08-19-2012, 05:58 PM

Sounds like a center support bearing to me.....Rich

300sdToronto · #3 08-19-2012, 09:34 PM

Any hints on how I inspect the bearing or otherwise figure out if it is good or bad?

ROLLGUY · #4 08-19-2012, 11:29 PM

Quote:

Originally Posted by 300sdToronto

Any hints on how I inspect the bearing or otherwise figure out if it is good or bad?

I think if you take the time to remove it (to inspect), you might as well replace it. It may be original, and time to replace it anyway.

dude99 · #5 08-20-2012, 12:23 AM

Might also be worth checking the flex disks. It does sound like the support bearing though.

toomany MBZ · #6 08-20-2012, 07:21 AM

Visually check the flex discs and can you rotate the center bearing?

If so, you may want to replace it.

300sdToronto · #7 08-20-2012, 01:28 PM

Of course, the car is not up on blocks any longer.

I assume the centre support bearing is half way down the driveshaft? Do I need to remove the metal cover or shield underneath the drive shaft to get at the centre bearing?

ROLLGUY · #8 08-20-2012, 01:29 PM

Quote:

Originally Posted by 300sdToronto

I assume the centre support bearing is half way down the driveshaft? Do I need to remove the metal cover or shield underneath the drive shaft to get at the centre bearing?

Yes

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