Play in the diff, thicker oil?

[M104]

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.

 

[ABN_CBT_ENGR]

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?

 

[tomcat27]

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

 

[M104]

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 :

 

[ripcord]

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.

 

[M104]

They're all good, not very soft but not cracked or torn, no play in them.

 

[ripcord]

They can look good from the outside but still be breaking around the bolt holes.

Note: not my picture, I linked to one online.

 

[M104]

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.

 

[ripcord]

You may very well be right about that. Internet diagnosis is very difficult

 

[WyrTwister]

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 .

 

[M104]

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.

 

[Donald]

Use the proper spec gear oil and fix what is worn or broken.

 

[Lubener]

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.

 

[M104]

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.

 

[bdcardinal]

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.