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940 Grinding/Screeching Sound Plus Stalling

FreeEMSFred

New member
Joined
Nov 2, 2009
Location
Kiwiland
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! :-/

Pop
 
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.
 
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.
 
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.
 
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
 
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.
 
I think there may be two issues related to the noises and behaviour I heard/felt/observed.

Recently been driving it again after a long time ignoring it and hoping it didn't get worse. Only managed to get it to misbehave a little bit a couple of times, nothing like that first day.

One of those times had no vehicle dynamics involved at all. It was very clearly an accessory locked up and belt shrieking as it stalled the engine. IE, aircon pump or power steering pump or alternator.

However I'll reiterate, the day it went haywire there was an obvious racket coming from the bell housing area that could not have been coming from anywhere else AFAICT.

Will keep updating this as I discover more or crush the car, minus the Polaris wheels, 7 seat setup, and fresh corner lights.
 
I have similar noise and one time stall in past month.
Same described noise and location except only while driving 10-20mph speed after letting car sit for a bit.
I was thinking mine is strut mounts bearing on the passenger side OR exhaust since mine is still original few times patched up and few times replaced cat converter.
 
Been driving it a bunch, I think two-noise theory is right, and both noises seem to have mostly gone. You can still provoke the ugly trans tunnel noise with enough RPM / sustained RPM, but otherwise it doesn't rear its head - perhaps self clearanced? or the unlucky rock fell out? No idea. One day, maybe, bigger fish to fry on that car though. Pic of the car in question with upgraded tail lights:

EJkndZeVUAAiWtU
 
Love those intermittent issues that make ya not able to diagnose without firing the parts cannon but that have ya wondering where she will leave you stranded!
 
She's been with her new owner for nearly a year now, and he's put more mileage on it than I did in 3 and that issue never came back. It must have been something in the bell housing somewhere doing that, and it must have just ground itself out in the end, I guess. Car has been mostly reliable save a few unrelated issues. I've helped the owner out with a few chores here and there :-)
 
Yeah, could be, however I couldn't see any evidence of destruction from something like that or a stone being trapped and I did at least try to look. I have an alloy trans brace from another B23ET engine that saw something like that and was completely eroded away though so I know such things do happen :-D
 
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