Play in the diff, thicker oil?

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Hello guy, one of the few problems my car has is a metallic clunk when shifting between gears and when i abruptly release the gas pedal or put my foot back on it. I had the car on ramps a few times and none of the bushings or flex-discs are shot, everything is tight. I was able to recreate the noise i hear while driving by turning the driveshaft by hand and noticed a play in the diff.

I know it should be possible to adjust backlash but this isn't a job i want to tackle and i've heard about the central pin in the diff wearing out and therefore making this clunk in these Mercedes differentials. I don't know what it is but as a short term solution, i thought about trying a thick xW-140 oil just to dampen the noise a bit before having the time to get this fixed. I suspect this wouldn't make any difference but maybe i will need to get the car up to change the fuel filter anyway, this would be the occasion to give it a shot.

The car made this noise when i bought it with 128k kms. I changed what i believe was the factory fill and it was nasty, really thick and black. I changed it for a 80W-90 that is on the thin side. 20k kms later i changed it again and it was perfect just like the day i pourred it in.
 
What you are describing sounds more like a U/CV joint going bad and not a issue with differential gears.

Have you checked the joints and eliminated them from the equation?
 
Your idea for thicker lube can't hurt, but I doubt it will reduce the noise much.
My 13 year old did the differential setup on our Cougar. Dial indicator, dye marking and adjusting the gear contact.

I tried to find a shop - nobody would touch it even two shops that specialize in drivelines
 
What you are describing sounds more like a U/CV joint going bad and not a issue with differential gears.

Have you checked the joints and eliminated them from the equation?
I will check again but am 99% certain. CV joints are tight but again i checked them with the wheels on the ground, not the best setup. I could hear the noise coming from the diff when i checked the play by hand and it was the same noise.
Your idea for thicker lube can't hurt, but I doubt it will reduce the noise much.
My 13 year old did the differential setup on our Cougar. Dial indicator, dye marking and adjusting the gear contact.

I tried to find a shop - nobody would touch it even two shops that specialize in drivelines
On the Mercedes W202 i would have to drop the diff to check it's internals. :/

EDIT : Here's something similar :
 
Is this one of the models with the flexible rubber discs on the drive line and axles? If yes, I would check that those are all good. They can start to develop cracks around the bolt holes and add a lot of free play. That diff does have some free play but I've seen a lot worse.
 
They're all good, not very soft but not cracked or torn, no play in them.
 
They can look good from the outside but still be breaking around the bolt holes.

106228d1350069704-drive-shaft-tore-off-flex-joint-disaster-flex-disc-change-5s-oct.jpg


Note: not my picture, I linked to one online.
 
Interesting, I was looking for this kind of cracks but obviously you can't see it with everything bolted on it. I noticed they are quite hard, not very rubbery. Still, i don't think such a play in the diff is normal and i can't see it not making this noise even with new flex-discs.
 
What you are describing sounds more like a U/CV joint going bad and not a issue with differential gears.

Have you checked the joints and eliminated them from the equation?
Exactly what I was thinking . Absolutely check the U-Joints , before you mess with the diff . Of course , draining and refilling gear lube is not going to hurt anything , no matter how often . As long as you use a quality product . Also check & make sure the pinion and wheel seals are OK .
 
Thanks guys, i will check for play in the u-joint again but i remember it being tight. I will keep you posted whatever i do, might be in a few weeks.
 
Thanks guys, i will check for play in the u-joint again but i remember it being tight. I will keep you posted whatever i do, might be in a few weeks.
To easily see any u joint play, you should raise the wheels off the ground, put the transmission in neutral.
Heavier oil is not going to take out any play in a differential.
 
The mechanic found the culprit ! It's the driveshaft itself, the splines where the two halves meet. Said it's not worn enough to be a concern besides the annoyance. I will start looking for a used driveshaft.
 

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Is there a grease that can be put in there to help with the noise? Ford has this issue on the F-150s and have a service kit, 9L3Z-4W602-A which includes a packet of grease and clamps.
 
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