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  #1  
Old 01-22-2009, 01:25 AM
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Scraping/whining noise

After many successful refurbishments to my 300D, thanks in very large part to this forum, the cold snap we are feeling even here in Florida has made a new gremlin appear that I'm not sure about.

When running from a cold start and taking it real easy, as soon as I get into third gear (~35mph, or lower even if I'm creeping out of the neighborhood first thing) I'm getting a sound from somewhere under the car (?) that is like a solid piece of metal lightly brushing against a hollow or flat piece. Kind of a rough "shing, shing, shing" noise.

The noise increases in frequency with speed until it becomes a steady metallic "shhh" sound of fair pitch at around 50mph. I opened the door once to hear it better, and it was pretty loud, but I could not localize it.

After a while of running when everything is warmed up, the noise is much less apparent on acceleration. On deceleration (using brakes) when warm, instead of a steady reduction in frequency back to "shing, shing, shing" as when cold, it becomes more of a turbine winding-down sound. The sound does not disappear if I coast when it starts happening.

I just got a new transmission mount and motor mounts but have not yet installed them. The installed motor mounts are completely squished with the metal shields sitting on the lower metal rims and the tranny mount just looks all cracked and crappy. There is pretty severe vibration if you really step on the brake coming to a stop (that continues once stopped). Vibration is still there on normal stops, just not as bad. When it's bad from a hard stop, putting it in neutral for a moment seems to help slightly. Vibes disappear with slightest forward movement in all cases. I was hoping that new mounts would solve some/all of the 'stopping vibe'.

After getting this noise and then reading through other messages on motor/transmission mount replacements, mostly SD related unfortunately, it seems like the mounts could cause things to be misaligned enough to cause the noise. Didn't seem like anyone was really describing what I'm hearing either though.

I got a couple of basic ideas on troubleshooting (checking the wheel bearings, brake dragging(not it, see above)), but I'm hoping for some direct advice as I'm feeling quite out of my depth with the driveline compared to adjusting valves and replacing filters! I'm a definitely a weekend warrior whose main mechanical experience has been with a couple of motorcycles that had fundamentally sound engines but were near death from neglect.

Luckily they are metric...

Any help or pointers will be most appreciated!
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Old 01-22-2009, 01:36 AM
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Damn cold!

I wonder if the flex plate cracked? is it an auto?
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  #3  
Old 01-22-2009, 01:43 AM
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There is a flexplate that mates the transmission's torque converter to the flywheel of the engine. A few members have posted failures of this plate and it is very replaceable. But I am sure it is no fun with the engine and trans still in the car.



Try to inspect the general area (bell housing) for metal shards.

*this is only one of many things it could be *
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Old 01-22-2009, 01:54 AM
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Yes peek through the Bellhousing window. You'll need to remove the black plastic covering, use a flashlight to peek in there and inspect all the bolts by turning the motor over by hand. You might find this. Pics of a Cracked Flex Plate
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  #5  
Old 01-22-2009, 08:33 AM
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Mine was doing that. I bought a new flex plate (called a washer by Benz), pulled it apart and..... nothing. Mine was perfect. Put it back together and only made it once sinc and it was light. A good mechanic friend said if it comes back put a coke can thickness shim under the starter. He said by removing and installing the starter I made just enough clearance to make it stop. If you do need a flex plat I will sell you mine. Paul
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  #6  
Old 01-22-2009, 11:05 AM
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Thanks very much for the replies. Yes, it is an automatic. I was afraid it might be the flex plate. Will try to get under it for a look asap. If it is that, hopefully driving as little and gently as possible will prolong the inevitable. Really mixed feelings about attempting DIY replacement on this. Seem to recall reading that it's a several hour job for a pro. Would be a nice opportunity to do the flex discs and support bearing though with the driveshaft out anyway. If all that's do-able without a transmission jack between Friday and Sunday sundowns, I may consider it. I'm guessing it would be 700-1000 bucks to have a pro do it. Cross that bridge if I come to it I guess.

There's one other symptom the car has shown consistently since I got it, but I'm pretty sure is unrelated. When starting off from a stop before the engine/transmission are fully warmed up, there is a wallowing sensation accompanied by a low pitch and volume grumbling sound until you hit about 10mph. Very light takeoff's lessen/eliminate it. Once everything is warmed up it stops doing it and you can nail the pedal off the line with no problems. Probably unrelated like I said, but I thought I'd throw it out there.
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Old 01-22-2009, 03:41 PM
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Try loosening and shimming the starter first. Can't hurt and I went through alot of headache to find out my flex plate was fine.
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  #8  
Old 01-25-2009, 11:46 PM
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Little update:

At 60-65+ degrees(F) ambient, the noise seems to (almost? may be imagining) completely disappear. Checked out the flex plate and all bolts are present, seem tight, and there are no discernable breaks or cracks in the plate around them. No debris beyond some small road bits in the chamber that I could reach in and feel. I need to get a cover for it or rig something as the original is missing. Definitely seems like something is just a little off like you are saying progun.
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