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Old 02-09-2019, 05:02 AM   #1
FreeEMSFred
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Default Grinding/Screeching Sound Plus Stalling

Let's start with this: Single weirdest noise I've ever heard come from a car in my entire life ~35 odd years I remember, ~25 odd driving, all makes/models in at least 10 countries.

Taking 2 friends and my wife down a windy country road in the 940 wagon with a bunch of gear in the back, not pushing super hard, but not pissing around, medium pace. Mostly 2nd/3rd gear from the AW71, a little 1st gear around the slowest corners and steepest bits.

Particular corner marked 25kph is good for 50+ in the right car and I guess I took it in the 35-40kph range, bumping the trans into 1st as I got below 50kph under moderate brakes into the corner. Half way around the corner the noise started.

Loud. Metallic grinding, bordering on screeching but not a rubber kind of screech. Noise persisted for the last few km to our destination and once parked. But varied significantly in style/character depending on accel/decel with idle being worst and cruising under mild load or more better.

Popped bonnet but noise came from the back of the engine, all front mounted accessories quite/normal. Noise obviously coming up from firewall direction. Sticking head under behind the front wheel it seemed to be coming from the engine's direction, indicating bell housing source.

Went out on the water for 10 hours and forgot about it.

Got in the car to leave after a great day and hit the key, noise starts immediately, and I wonder "will we make it home". No choice at 1030 at night in that location, so off we went. A couple of corners into the windy road and on lift off/up shift the engine *stalled*, felt/sounded like it was stopped *by* something. Yikes. Hazards on. Into neutral, hit key half expecting failure to start, started fine, back into drive, off we went. Figured out that it made less noise and was less likely to stall with food on gas a bit, so did that the rest of the way as much as practical.

Dropped one passenger off in the city, pulled out of his building's driveway and a more obvious stall. You could hear what sounded like teeth carving through alloy bring the engine to a stop. Had me convinced it was flex plate failure. Had my wife cross her legs on the passenger seat so as not to be in line of fire if it failed and grenaded somehow, and tucked my left leg up on the seat, too. More noise all the way, but motorway cruising with light/moderate throttle made less. Left next drop off and made it home okay, pulling into the drive possibly waking people up with the noise still happening.

Parked for 2 days unmoved. Fired it up tonight and chucked a jack under it and no noise. Pulled lower inspection covers/vent covers and torque converter, ring gear, 60-2, etc all look fine/normal/unharmed, no sign of any metal shavings or anything of the kind. No evidence of a rock stuck in the bell housing doing the rounds or machining the rotating bits. Nothing.

Took it for a test drive, nothing, nothing, nothing, turned firmly into a side road on the gas in 1st and bang, noise starts loudly again, persists until almost home to see if I could hear the source, and stops just shy of the driveway. Another lap, no noise.

I currently do not trust the car. But to my ears and understanding of all bits of a redblock auto driveline, it doesn't make *any* sense at all. None. However I don't understand the innards of the auto box overly well, so I'm now thinking it's something failing inside the trans?

Checked/dipped oil, auto fluid, power steer ATF, all good. No sparkles.

There's going to be metal shavings somewhere, no way can that much noise happen without some damage.

Thoughts? Theories? What am I missing? Can an auto trans soaked in ATF make those sounds? To my ear the noise sounds dry, but that could easily be wrong, I suppose.

Help! :-/

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Old 02-09-2019, 06:11 AM   #2
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You didn't by any chance bust an engine mount...?
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Old 02-09-2019, 12:55 PM   #3
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Have you been into the cover over the intermediate shaft lately? This requires a gasket not FIPG for proper clearance of the thrust bearing.
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Old 02-10-2019, 07:44 AM   #4
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Engine mounts are good, later hydraulic type, in good condition, visibly doing their job when jacking/dropping/revving/etc.

No, engine remains unopened, however after a severe overheating about a year ago it developed or worsened a head gasket oil leak that's annoying but not critical.

I think I took some video of the sound. I will try to upload it tomorrow and link here once I do.
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Old 02-10-2019, 08:44 AM   #5
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Destroyed cam by warped head?
Noise is related to revs?
I know a cracked flex plate will make strange noise too

Good luck, Kay
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Old 02-10-2019, 05:56 PM   #6
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I had screeching sound under the hood of the Mercedes. Intermittent. For at least a few days. Hmmmm.... Couldn't find a source of noise... Seemed like in the block (wth?) Gave it a serp belt and idlers. Started up quiet. Pulled out for test drive when it spat a front main bearing shell into the chains. Find the noise OP.
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Old 02-10-2019, 06:40 PM   #7
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Quote:
Loud. Metallic grinding, bordering on screeching but not a rubber kind of screech. Noise persisted for the last few km to our destination and once parked. But varied significantly in style/character depending on accel/decel with idle being worst and cruising under mild load or more better.
If I recall, a bunch of the planetary gears are still moving inside an automatic transmission even while in park. To confirm... does the sound vary with car traveling speed, or with engine RPM? If the former, then that likely points to the transmission and not the engine.
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Old 02-10-2019, 11:54 PM   #8
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My 940 with an AW71 would do this occasionally. Seems like it would do it under load while going up a hill? I never figured it out and all but basically went away. Never figured it out myself
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Old 02-11-2019, 06:29 AM   #9
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Kestrel, that's a good point. I'm not sure it correlated with either, which makes no sense at all. If anything it seemed low *vehicle* speed brought it on and higher vehicle speed diminished it. I think. Not confident in that though.

Given what's inside an engine, I strongly doubt the back end of the crank is capable of noises like that. Short of some end float and tight tolerances being exceeded, perhaps? Just speculating.

And no, no video. But it sounds like I'm not alone, anyway.
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