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  #1  
Old 09-01-2011, 10:49 PM
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Strange Noise 1980 300D

Just got the car a couple of weeks ago, runs great, drove it on a business trip about 600 miles round trip and no issues. Noticed yesterday when slowing down, between 3-4mph I have a grinding noise. Sounds like worn brake pads, rubbing the rotor. The sound is there whether I am using the brakes or not. Inspected the rotors and they look fine, through the wheel. Looked underneath and the rubber boots on the CV joints looked fine. Next step is to raise the car and check the wheel bearings. Any other ideas about what this could be?

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  #2  
Old 09-01-2011, 11:28 PM
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How about the inside surface of the rotors?

Sixto
87 300D
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  #3  
Old 09-02-2011, 10:13 AM
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Thanks, I am going to look into a little more this weekend. It looks like I have to take the wheel off to check the inside of the rotors. I think it has to be brake related.
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Old 09-02-2011, 10:17 AM
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I'd start with the brakes. Could be pads all worn out. Or it could be a dragging brake. Feel the rims after a decent length drive. If one feel much hotter than the others you've got a dragging caliper.
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  #5  
Old 09-02-2011, 04:03 PM
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Comments based on assumptions due to post-count:

The parking brake on these cars is an internal drum on the rears, so if the noise is from the back, it may be there. Or it may be something like a broken spring inside the rotor. They're not too complicated, but can be a rusted dirty mess depending on location.

The pads on the brakes are easy-as-pie to remove and check. But the calipers trap a lot of dust and dirt. If the pads are dragging just a bit, you can thoroughly clean the calipers, use hi-temp brake grease on the sides to lube them.

You may get various input about collapsed brake lines. Maybe, maybe not.

Since you just got the car a few weeks ago, a brake service to include a fluid change may be in order anyway if the fluid's dark. Plenty of info here on those topics.

Grinding noise could also be a bearing. Another not too difficult task with plenty of info.
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  #6  
Old 09-06-2011, 09:19 AM
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The noise is coming from the exhaust system. At idle the muffler and hangers are vibrating causing this noise. The rubber hangers look fine, anything else I can do to fix this?
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Old 09-06-2011, 08:23 PM
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What's the condition of the motor mounts? At idle in gear, or N, or P?

Even though a "grinding noise" from the first post doesn't sound exhaust related.
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Old 09-07-2011, 11:53 AM
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Actually as odd as the description may sound, I have the same thing on my '85 -- but only when the AC is on.

It SEEMS like a low-speed grinding because from the driver's seat you become aware of it when the engine slows down close to idle at very low speed (especially in a parking lot), and there is less road/drivetrain noise in general to mask it.

Took me a while to figure it out. First time I was sure I had a dragging park-brake pad. Then I realized it was doing it briefly when the car was stopped, more so on really hot days.
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2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

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  #9  
Old 09-08-2011, 12:27 AM
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I looked back under the car and noticed one of the rubber hangars for the muffler was broken, this explains the vibrating and the noise when coming to a stop. Can I buy generic rubber hangars at the auto store? By the way, how smooth do these engines run when idling in park and drive. When sitting in the drivers seat, the car vibrates, more so in drive when stopped, less when in park. How can I tell if the car idles right? But runs pretty smooth when I give it gas. The engine and transmission mounts where replaced in 2008 and less than 3K miles on them. How can you tell if they are bad?
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  #10  
Old 09-08-2011, 07:34 PM
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If the generic doughnuts fit, they'll do the job. If they don't fit, the others are pretty cheap.

"Idling right" is relative.

As a new-ish owner, if you haven't done the obligatory valve adjustment, then you're overdue. That will either improve the idle, or at least eliminate valves as an issue.

I found a few tanks of biodiesel smoothed the idle. Maybe coincidence and wishful thinking, maybe improved fuel delivery. A diesel purge is sometimes recommended, sometimes dismissed as snake-oil.

Regardless, clean filters, quality fuel and a valve adjustment should be the baseline. If the idle is still rougher than you'd like you can always look for more: injectors, engine shocks, etc.

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