I need help identifying the source of a noise that I think is coming from some part of my manual transmission (but I don't know that for sure so don't jump to that conclusion right away ).

This is for a 1984 190D-2.2 with 5-speed manual transmission.
250k miles on the car, and maybe 90k miles on a new, dealer-installed manual transmission (p/n 124-260-00-01, I think it's a 717.410).

In the past month or so, a warbly whirling sound has started. My wife described it as a muffled version of the sound turkeys make. It's hard to describe a noise in writing, so I'll also mention that it's *not* a grinding, scraping, or rumbling sound, nor is it a shrill squeal. A whirling sound is the best description I can come up with.

It is only present when there is a load on the drivetrain, either while accelerating hard, or while decelerating in gear. The sound is not vehicle-speed-dependent and is not there when cruising at a steady speed.

The easiest way to cause the car to make the noise is as follows:
1) Coast along at speed (25, 45, 65 mph - doesn't matter) with the clutch pedal depressed and the transmission in gear (no noise yet)
2) Release the clutch pedal slowly - as soon as the clutch starts to engage the noise appears, and continues as the car is decelerating while in gear.
3) Gently step on the accelerator to stop the car from decelerating - the noise goes away.
4) Mash the accelerator to the floor - the noise comes back.

In step 2, the noise is the same in pitch and volume regardless of vehicle speed or transmission gear (I only tried gears 2, 3, and 4). It slightly decreases in pitch and volume as the engine & vehicle speed drop while decelerating.

It's hard to tell, but the sound appears to be coming from somewhere forward of the middle of the car (i.e. it doesn't sound like it's the driveshaft support bearing or rear axle or rear wheel bearings, and the lack of dependence on vehicle speed seems to support this observation). This leads me to think it's most likely a transmission or clutch thing.

The noise isn't there when the car is stopped (clutch pedal depressed, or clutch pedal out with transmission in neutral). If you rev the engine (while the car is moving or stopped) with the clutch pedal depressed, the noise still isn't there.

The noise also appears in a slightly quieter form during really hard braking, with or without the clutch pedal depressed. Here I speculate that this is because the hard braking is causing the driveline to decelerate, much like the engine-braking scenario described above.

Transmission fluid level is OK, fluid is Redline MTL, last changed maybe 2.5 years ago.

If anyone has come across a similar noise or knows what this might be, let me know. Or, if you can think of another test to help diagnose the problem, that would be great too.

Thank you!

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1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

Should not be present already at ninety K since installed if the transmission was new. You are basically describing the possibility of a bearing going bad in the transmission. Hopefully it is something else.

At the present time I have a car doing exactly the same in a toyota echo five speed at about 150 k miles or 240 K kilometers. It is slowly getting worse. Originally it was only noticeable at periods of changing loads. Now it is constant maybe four K miles later.

I think It is the driveshaft carrier bearing or mount.

I wouldn't expect the driveshaft carrier bearing to make a sound if it depends on accleration and deceleration (or at least I hope because I'm about to replace mine because of a noise I hear at all speeds).

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

My driveshaft support bearing is actually bad too. It's failed for the 3rd time in the past 60k miles so I'm familiar with that sound too, unfortunately. The winter slush and salt and sand seems to be hard on it. It's an easy one to diagnose; totally vehicle-speed-dependent and if you put your ear to the floor in the back seat you can hear it clearly. Previous times, I just replaced the bearing. This time, I ordered a repair kit from the dealership which comes with some extra metal caps to shield the bearing from dirt and grime.

Anyway, back to the original problem, I'm about 90% certain that it's not the driveshaft bearing (since it's bad and I can hear it as a distinct, separate noise), but I do appreciate the suggestion!

Part of my motivation to fix the 'mystery sound' ASAP is because I plan to take the driveshaft out anyway to replace the support bearing, so while the car is apart I'd like to do anything else that is needed.

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1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

If its a gearbox bearing, you are looking at a rebuild or replacement.

It sounds like a gearbox bearing problem probably not the main shaft bearings, they could be bad as well though.

If not fixed early, you may have gear/shaft damage.
It would be worth examining the oil for metal particles.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I went to a transmission & clutch shop and one of their guys test drove the car with me for about 30 minutes. He thought there was nothing wrong and didn't hear anything abnormal. They didn't charge me for this, which was nice of them. He said that the first thing they'd try is changing the fluid in the transmission.

So, on the advice of a post on this forum from Marshall Booth (who owned several 190D 5-speeds), I changed from the Redline MTL fluid to Mobil 1 Synthetic ATF. No change whatsoever in the noise. The original fluid level was fine and the fluid didn't appear abnormal or contain any metal chunks.

On the weekend, I replaced the driveshaft support bearing and changed the differential fluid (using a synthetic gear oil). One of those two things fixed it - the noise is 100% gone. I would have expected the noise to be more vehicle-speed-dependent if it came from the bearing or differential, but what can I say - it's fixed.

So, to the person who said that it might be the driveshaft support bearing (and I disagreed ), there's at least a 50% chance that you may have been right after all! I would have liked to have changed the bearing and differential fluid separately to totally confirm the source of the noise, but it was more practical to do both jobs at the same time. At least it wasn't a transmission problem - that's a relief!

Thanks again to everyone for your suggestions and advice.

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1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

Yes it was great that the transmission bearings where not the issue. I have been hearing more complaints recently on manual transmission bearing issues on non mercedes cars.

It may be because the cars are staying on the road till higher total milage than they ever did before. Or the manufactures may be using lesser quality bearings. In my toyotas case I was suprised they sold a complete bearing kit for my transmission then found out it was a common enough problem with this brand to justify it.

Yes it was great that the transmission bearings where not the issue. I have been hearing more complaints recently on manual transmission bearing issues on non mercedes cars.

It may be because the cars are staying on the road till higher total milage than they ever did before. Or the manufactures may be using lesser quality bearings. In my toyotas case I was suprised they sold a complete bearing kit for my transmission then found out it was a common enough problem with this brand to justify it. Toyota seems to have kept the issue quiet.