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Old 10-13-2018, 10:22 AM
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The Howling-1987 300TD

I have a mystery howling noise in my 1987 Mecedes 300TD. When it started, I thought the muffler was going out, but I liked the low rumble. Then it got increasingly louder. Today, it is loud at 15mph and at 60mph it is unbearable. Because I had already replaced all four wheel bearings, I first suspected the rear differential. When I dropped the gear lube, it came out nice and clean. I refilled the rear transaxle with transmission fluid to see if the noise would change. After 100 miles, I replaced it with clean gear lube. There was no sound difference and the fluid was clean. Then I suspected the center bearing of the driveshaft. I had the entire driveshaft assembly replaced with no difference. It sounds like it is coming from the left rear, but my ears cannot be trusted. I replaced the left rear half-shaft and the sound still did not change. "Howling" is the best description I can think of. The sound does not change when I accelerate or decelerate or swerve. It gets progressively louder with speed, but not with engine or transmission RPM. Does anyone have any ideas?

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Old 10-13-2018, 01:44 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
I know you've already done this, but it sure sounds like a rear wheel bearing has had a short life. There have been several reports, here on the forum, about cheap Chinese wheel bearings showing up with premature failure.
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  #3  
Old 10-13-2018, 04:50 PM
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Does the sound get louder when you turn? Typically, wheel bearings make more noise when you turn away from the bad bearing. I had an aftermarket rear bearing go in just 50K miles.
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Old 10-13-2018, 06:14 PM
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Join Date: Mar 2008
Location: Buffalo NY
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If you put it up on stands, you can run it and listen for the source of noise from underneath.
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Old 10-13-2018, 07:37 PM
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1987 w124 300D
 
Join Date: Mar 2008
Location: Edmonton, Canada
Posts: 1,539
Rear end jacked up so both wheels are off ground, put in Neutral, turn car off.

Place your fingers against the wheel hub carrier near the center where the bearings are and rotate the wheel (either direction). If it feels anything other than smooth, like if it feels "gritty"... it's a wheel bearing.

Compare to the other side to convince yourself.

If you have a mechanic's stethoscope, probe around near the bearing on the back of the hub and you might be able to hear the bad bearings grinding / scraping.

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