Mercedes driveline rumble

[OM605]

I've had the car for almost a year and have been trying to get rid of various vibrations as much as i can had no luck solving this rumble issue. I have other unrelated vibration issues (engine vibrations due to poor quality motor mounts and a bad rear muffler).

It's more a feeling than a bad vibration that shakes the car. It's hard to describe but it feels like something is out of balance at all time and the noise level inside the cabin is pretty high. I think it is worse around 90 kmh and i can feel it even more when the road is nice.

So far i've had 4 new Goodyear tires installed, balanced twiced, new flex discs and new carrier bearing+bushing (the rubber was collapsed and i thought it was the issue), new trans mount. Rims aren't bent or damaged and rear diff mounts are tight. I've even wire brushed the surface between the rims and the hubs and tighten the lug nuts to spec and it didn't help. U-joint is tight too. I made sure both parts of the driveshaft are aligned as they should.

I've made a few other observations. When i grab the axle shafts near the diff i can feel and see some movement but i have no idea what kind of play is allowable in the diff bearings or even if the play is in the splines or the bearings.

Over the months i've realized that i seem to forget the issue more when the trunk is full of stuff or if the tank is full. The rumble is still there is neutral or any gear, under load or on decel and i've also tried cornering hard many times and rulled out wheel bearings (at least the front ones).

I'm curious to see what you think, this is not an easy one for me...

 

[Cujet]

It is good to note that many vehicles simply have a resonant speed at which noise and vibration are felt. This may happen when the engine, transmission and driveline are completely locked together. In the case of an automatic, the converter locks up, and in the case of a manual transmission, the car is in gear and the minor movement allowed by the clutch springs may in fact be in sync with the dynamic resonance.

Often, as vehicles age, these noises become more pronounced. As you noted, engine mounts, transmission mounts and differential mounts can play a role. Along with shafts that may be out of balance or out of round.

CV joints typically have some movement, but should run true and be vibration free.

Does the vibration go away upon throttle lift or in neutral?

 

[OM605]

Does the vibration go away upon throttle lift or in neutral?

No, throttle input or being in gear or neutral doesn't influence the noise/vibration at all.

 

[GMBoy]

I had a 2010 CLS550 in the shop for that had the same condition you experienced - it was the driveshaft u-joints. Had a driveshaft shop replace them and balance the assy and issue was gone.

 

[CDX825]

Drop the drive shaft and check how the u joints move. They should turn freely without binding. If you turn them from side to side and they bind up at all they need replaced. Just because they dont have any play in them doesn't mean they are good and you won't be able to tell if they are binding up when on the vehicle.

 

[OM605]

I'm going to ask the mechanic who installed the flex discs and carrier what he thought of the condition of the u-joint.

 

[OM605]

Went and he told be the u-joint was good, no binding and no play. He thinks i'm on the right path looking for something wrong with the CV axles and bearings.

 

[OM605]

Just drove the car again on a nicer section of road and to me the replacement of the carrier made things worse. It wasn't as bad before. This is doing my head in, almost thinking about getting rid of the car.

 

[OM605]

Found it! Pretty sure this is it: went under the car again and had a better view at the factory marks on the driveshaft and they're not aligned as they should. Took a rope to make sure it's not in my mind. I think it's off by one spline but enough to cause the whirring noise and vibration.

 

[sloinker]

I had a RWD Mercedes and I had to replace the rubber flex joints to get rid of vibration once. They had dry rotted and were coming apart. Sounds like you have something different than I did.

 

[OM605]

Front flex disc is only 6 months old and still looking like new and rear one was replaced a few days ago while relpacing the carrier.

 

[IcarusLSC]

edit, you checked this stuff already sry

 

[OM605]

Those shafts are splined to only go in one way from what I recall. It most likely is the center carrier bearing, or surround on it getting real soft.

I have seen two driveshaft, one from a W124 and one from a W211 and they weren't, i don't imagine the W202's driveshaft being any different unfortunately. The whole carrier is brand new.

 

[Chris142]

Drop the drive shaft and check how the u joints move. They should turn freely without binding. If you turn them from side to side and they bind up at all they need replaced. Just because they dont have any play in them doesn't mean they are good and you won't be able to tell if they are binding up when on the vehicle.

it dont have those. it uses flexable rubber discs instead

 

[Chris142]

test the motor mounts

 

[OM605]

test the motor mounts

They are new too, of poor quality but new. This whirring vibration didn't exist before i took the car to the shop to have them install the new carrier.

 

[Astro14]

Even one spline can cause balance errors in a driveshaft. When replacing those rubber flex discs, MB is very particular about keeping that alignment.

Have the shop redo it, then see what you got

 

[OM605]

Even one spline can cause balance errors in a driveshaft. When replacing those rubber flex discs, MB is very particular about keeping that alignment.

That's what i am thinking indeed. There's a reason those marks exist. If i am not mistaken there are 27 splines. 360° divided by 27 means it's probably off by 13.33 degrees.

Ever seen this video? Shows how sensitive driveshafts are to proper balancing.

 

[SubieRubyRoo]

No, throttle input or being in gear or neutral doesn't influence the noise/vibration at all.

Based on what my brother has told me over the years, this means it’s in the tires and/or wheel bearings.

Vibration/noise when in gear means it’s in the trans/driveshaft(s).

 

[OM605]

Based on what my brother has told me over the years, this means it’s in the tires and/or wheel bearings.

Vibration/noise when in gear means it’s in the trans/driveshaft(s).

But the driveshaft is always turning as long as the car is moving, i don't see how being in neutral would make it more "balanced".