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Old 09-01-2021, 12:04 PM   #1
SalvadorPalma
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Default My 940 is making a weird noise when reversing

My car is a 940 Turbo Wagon, B230FK, M90 Transmission.

It has been making this noise while reversing. It seems to only make the noise at clutch point. I don't know if it's becuase the noise is transmission or clutch related, or simply becuase when the car picks up speed, the noise stops.

Need help diagnosing please.

Here's a video of the noise: https://www.youtube.com/watch?v=F9-776vCjaI
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Old 09-02-2021, 04:58 AM   #2
Janspeed
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Because you say (and i heard it in the video) that the sound happens at clutch (engagement) point i think it might be a worn friction plate and the sound might be metal on metal contact (rivets?).
Another possibility: your car is a late model M90 car. This means it has a dual mass flywheel. That could be broken as well.

To really be sure there is no escape, you will have to take the gearbox off and inspect all clutch parts, throw out bearing and flywheel.
( before you take the flywheel off make SURE you mark the position of the flywheel IN RELATION to the crank. If you re-install it clocked wrong the car will not start.)
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Old 09-02-2021, 05:57 AM   #3
Fa182
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Can't help other than to say I've experienced this too.
Suddenly had that sound appearing when taking off in first gear on my 940 a few times over the last few years (can count on one hand though).

As OP said, it only happens when everything was cold and always when it was a bit cooler outside.
Still quite randomly though.

I've had the dealer replace the rear main seal about 2 years ago and they said the clutch and everything is in perfect condition.

I have no idea what's causing it and would be curious to know as well.
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Old 09-02-2021, 07:56 AM   #4
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The fact that your car only does it in reverse may mean the problem is something else.
Although I just did a clutch job on a mint 740, that did a kinda similar sound during heavier clutch usage. It was doing it for years, but started slipping at full throttle only during the last weeks. Months ago i drove the car a bit to realise that i can reproduce the noise, with holding the clutch pedal in a certain position, applying throttle.

During disassembly, i seen a bit too much amount of grease on the input shaft, and it also seemed that the pilot bearing was puking out its grease. Clutch disc looked pretty normal, but both friction surfaces (pp and flywheel) were fully brown, which i never seen in my life.

Installed a new bearing, cleaned the bellhousing, resurfaced the flywheel with 100grit sandpaper, installed a lightly used pp and disc, lightly greased the splines, pivot points, assembled, no more noise and its better than ever. Owner says cluch now grabs way quicker than before.

Also the M90 does not use a pilot bearing, so it could not puke out its grease.
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Old 09-02-2021, 03:36 PM   #5
SalvadorPalma
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Hey guys so after going nuts over this for 2 days I think I finaly know what's going on with my car.

I am yet to completely confirm this. But I'm very confident saying that in this situation this noise is due to low fluid level on the transmission. It was pointed out by someone on volvo forums uk that it could be the reverse idle shaft making the noise, because it was above the fluid level (or rather the fluid was bellow).
This was made worse by the fact that I've been parking the car downhill recently, so the already low fluid level was pushed to the front of the transmission.
This theory is further validated by both the fact that after driving for a while the car would stop making the noise (because it got lubricated during driving) and by the fact that swaping the direction of the car at the parking spot, with the front of the car facing up, forcing the oil to the rear and therefore submerging the rev. idle shaft which caused the car to not make this noise anymore. (It also never did it if the car was parked on level ground, I just didn't connect the dots)

I'm yet to check the level because I'll just order the oil first. But I'm pretty sure that's it. Quite a weird one I guess.

For future reference if anyone has a weird accute squeaking noise only in reverse driving uphill that goes away after driving a bit, check the tranny fluid level.
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Old 09-02-2021, 04:18 PM   #6
283SD
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A friend of mine had me rebuild the diff for his V8 MGB. Nothing really wrong with it, but he wanted all new brgs/seals,ect. A few weeks later he calls me a said that it made a terrible noise when he backed up. Brought me back the rear and he watched as took it apart again, nothing,nothing was wrong. Put in the car again, this time it made noise in 1'st and reverse. turns out the clutch disc was oil soaked causing the chatter.
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Old 09-03-2021, 08:49 AM   #7
Janspeed
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goes to show, never completely go by the assessment of the client/friend, always do your own diagnosis and try to get confirmation. Then draw your own conclusions.
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Old 09-07-2021, 10:26 AM   #8
SalvadorPalma
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UPDATE

It took me a while because the plug wouldn't come out so I had to order a breaker bar.
Today I went under the car, with the front on jack stands (not too high, but high) and when I opned the fill plug, oil started coming out. I lost a bit of oil but not too much I don't think.
This leaves me with 2 question:
First: Is it possible the front was too lifted that the hole was dropping oil even though the level was low, or does this defenitely prove the level wasn't low in the first place?
Second: Does the car need to be absolutely level in order the change transmission oil?

I kind think the car's front wasn't lifted enough for the hole to drop oil if the level was low to begin with. So that leaves me with the same issue from before, but more confused than ever. Because the theory did make a lot of sense, since the car stopped making the noise when I started parking uphil isntead of downhill.


PS: the oil that did come out looked super clean and didn't smell bad or anything.
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