940 weird sound from diff or driveline

[Jelle9990]

Hello everybody!
I have just resently bought myself a 93” 940 2.3T 4 speed with overdrive. I have really started to like this square turbobrick and i want to keep it (hopefully for a long time)
It is NOT in the best shape(yet) but im slowly maintaining and upgrading here and there.
Today it started to make a strange noice from the rear, maybe differential or driveline i think?
The best way i can describe the sound is if you put cardboard in your tire on your bicycle when you were a kid but muffled alot... it “clunks/rattle” rappedlyer the faster you go from 10-120 km/h
It ONLY maskes the sound with 1-3% throttle, not when im rolling, past the 3%, half gas or full throttle....

I really hope you guys can give me some help...
Best regards from the Danish volvo noob...

[Laird Scooby]

From your description it sounds as if you have either a worn or dry diff, if it's not dry i'd certainly think about draining and renewing the oil in it, perhaps adding a treatment to it.

It could also be the propshaft centre bearing but what you've said points more to the diff.

Has it been lowered or are the rear springs weak?

[Jelle9990]

Okay i want to change all the fluids engine, trans, and diff so i Will try that first... how do i check that bearing?
Nope its completly stock ride height and suspension seems just fine

[Laird Scooby]

Chances are the fluid changes will quieten the diff down, as you're doing it anyway i'd try that first. The prop centre bearing is usualy a whine or rumble that varies its pitch with speed and seems to come from just behind you under the floor, which is more or less where it is anyway.

Could also be worn universal joints, worth checking those as well.

A useful little tip for refilling the back axle is to remove the load space floor (i'm guessing you have an estate/Kombi) which is only 3 nuts, remove the fuel tank sender/pump unit access panel from the floor (4 screws) and feed a funnel with a piece of hose into the space, crawl under and push the end of the hose into the fill hole on the diff then you can lay inside and pour the oil into the funnel.







Gives you an idea!

[Jelle9990]

Ill give it a look. I just couldnt figure it out because it only made the sound when i was barely giving it gas like i was describing in the post above...

No its not an estate but a sedan

[Laird Scooby]

Originally Posted by Jelle9990

Ill give it a look. I just couldnt figure it out because it only made the sound when i was barely giving it gas like i was describing in the post above...

No its not an estate but a sedan

Maybe my method for refilling won't be as much help for you then but hopefully gives you some ideas.

As for why the noise was most prevalent when you were barely giving it anything, that's the time when you get the most backlash through the diff (or universal joints) as the speed of the diff is matched on the input and output so the gears are free to move in relation to each other. Give it some beansand the propshaft is trying to speed the diff up so the gears are held tighter to each other and vice versa when braking.