Glyn M Ruck

OK - well we are making some progress which can be difficult with multiple faults. I'm pleased.

Next step - Your car is RWD & not 4Matic - Yes? You are going to have to listen very carefully as to where the noise is coming from. If it's the rear & speed dependent then you must check tyres, wheel bearings & hope it's not the diff itself. If it's the diff pinion bearings that have lost preload then the noise should change from power on to trailing throttle. Try this. Also check the rear side shaft CV joint boots for cracks & grease leakage.

If the noise is front of car the engine belt tensioners & pulleys become suspect. If it is center of car it could be the torque converter & input shaft bearings. You need to track down where the noise is coming from.

Good luck!

panzafio

Dr Ruck, thanks for the quick reply. Yes its just RWD. When I removed the propshaft to remove the center shaft support, I noticed a collection of oil spray on the tunnel that definitely came from the U-Joint. Come to think of it, there was also oil spray on the transmission tunnel by the flex disc in the front.The Flex discs at the tranny and at the diff looked fine. When I drive the car, its hard to tell where the sound is comming from. I tried putting the car on jack stands and turning the ESP button on the dash off so that rear wheels could spin freely but that did not work.
Also, I spun the rear wheels by hand and tried to move the rear rotors. I removed the brake pads and they did not move. Does that mean that the rear bearings are good?? When I had the propshaft off yesterday, I tried have the bushing on it replace but I could not find a local machine shop that would do it. It seems like I may need to go to a local mechanic to put it on a lift and to put it in that special mode to turn the ESP completely off. the tyres do show a little feathering but did not seem to be the problem.the noise is speed dependent with pitch changing from low to high. I probably wont get to until Saturday. Thanks for your help.

panzafio

Took my 2002 c240 to a local mechanic and we went for a test drive. He said the noises while driving are not from the tires or the engine. It almost seems like two noises to him. While driving on the freeway here in So Cal back and forth to work it almost sounds like a high pitched whistling sound at 80mph. Around 60mph tonight it almost sound like the U-Joint. never really noticed it unless its getting worse. Anyways, the local mechanic said to come back and he will put it on a lift and try to diagnose it some more.

Glyn M Ruck

Diagnosing noises from halfway round the world is difficult. You are doing the right things now. You have to find the location. UJ's don't usually make high pitched noises but there is always a first time & if it's throwing grease - check it. On a W203 - tyres & wheelbearings are easily confused. Make sure it is not something stupid like wind noise on a loose heat shield around the exhaust. Also ensure transmission fluid level is correct. These cars do hit a natural harmonic with the diff at approx 80 Km/h not MPH. But it is so slight that most people would not hear it. Make sure the propshaft spline is properly greased.

Good luck!

panzafio

Dr Ruck, thanks for the quick reply. To answer your questions, the Heat Shields are on tight. I was wondering if I could actually remove the ones around the prop shaft and see if the noise changes while driving. Also, I put some white grease on the spline in the center mount too. Hopefully we can figure this out one noise at time. Thanks, for your help.

panzafio

So I just dropped off the C240 to the local mechanic and found that is was the Pinion Gear in the Differential. For $800 dollars he will replace it with a used one which he said he would have it done today. He said that they hardly go bad. hopefully that's it. Thanks for everyones help and especially Dr Ruck.

Glyn M Ruck

Pleased you found it. Make sure he gets the correct ratio replacement diff. A used diff is a fairly safe bet on these cars.

panzafio

Dr Ruck, Yes, that was the first thing that he had told me that he had to do. He said that the used diff he was going to use had a gear ratio that was closest to what I had. I just hope he put new gear oil in. thanks again for your help on this issue. I just really disappointed with the dealership that told me the before they could diagnose the car further they had to change the motormounts and the transmission mount. I cannot beleive that they did not know about the rear diff. Once the independent mechanic had it on a lift, you could totally tell it was the diff. i could hear it from the waiting room. I am definitely not going there again. Take care and thanks