W202 C240 unpleasant noise from drivetrain under deceleration.

[steveE250]

Hi, my last post was about a S203 C220 CDI that i ended up not purchasing due to auto gearbox problems. Well I needed something estate shaped in a hurry and I ended up buying a S202 C240 Sport. It has 235K miles on the clock and looks like it has been well looked after by at least some of its previous owners. I have now done most of the things that I needed the car for urgently and put nearly another thousand miles on it. It does have a problem however, which is much more apparent with the window or windows open in the recent lovely weather. Between about 40 MPH and 15 MPH whilst there is a lot of engine braking (foot of the throttle) there is a constant noise which reminds me of an idler bearing that is about to fail. My wife says that it sounds like an old fashioned bacon slicer. The pitch is related to wheel speed and the loudness to the amount of deceleration. Just a touch of power stops the noise and a bit of brakes quietens it right down. There is no trace of the noise under load fast or slow. There are a few slight noises from the diff and the gearbox but I dont think this noise is from either of them. It seems kind of like it is coming from somewhere in between. So far I have not investigated the cause of the noise. but I thought I would ask if the description sounds familiar to anyone first. I have quickly grown to like the car and already like it as much as my old C250 Turbo (RIP).

 

[Uncle Benz]

Sounds like noise on the overrun then. Almost always differential pinion bearing.

Propshaft centre bearing always worse under load in my experience.

 

[LostKiwi]

Check all the exhaust hangers and heat shields. Not uncommon for heatshields to come loose and make an odd noise.

 

[EmilysDad]

I agree with Uncle Benz. Exactly what I had with the diff of my Senator cured by nipping up the pre-load of the pinion bearing .... best guess.

 

[steveE250]

Thanks for those ideas. I will try to get it up in the air this weekend. the noise does not sound like it is coming from the diff unless its being transmitted back up the propshaft. there are a few minor moans and groans from the diff depending on load that do sound like that's where they are coming from.

 

[steveE250]

Ok, I got underneath this morning, just on jacks and axle stands. Not my favorite thing to do on a Saturday morning these days. There is quite a lot of exhaust and heat shields in the way but I can say that the UJ in the middle of the propshaft is knackered. If i rock the back wheel i can hear the play ringing up the propshaft and the pitch is the same as the horrid noise. I can just about get my hand in to turn the propshaft and I can feel and hear the play from the UJ. I have never had a failed UJ make that sort of noise and just on overrun but I have a feeling that it might just be the cause. Has anyone out there had a similar noise from a worn out UJ. It looks like a horrid job to do in the drive.

 

[LostKiwi]

I take it you mean the rubber donut?
Not that bad. 6 bolts and lever it out. Lever in new and refit bolts.

 

[steveE250]

Hi, I dont think I do mean a rubber donut. I cant see or get my hand that far but I think there is a center bearing and a UJ that I cant see under the heat shield If I grab the front part of the propshaft as near to the center as I can get my hand and turn or push and pull it up and down, it there is a small amount of play that makes a metalic ring. I can also get the same sort of noise from rocking the rear wheel. The car is nice and smooth to drive and my previous experience of failed UJs has usually resulted in vibration when driving. But then the UJs have been at either end of the propshaft on non Merc. cars.

 

[LostKiwi]

Ah ok. That requires propshaft out and replace joint (probably easier to swap propshaft).
My Defender used to 'ring' sometimes when a UJ was on its way out.

 

[steveE250]

That's Just what I was thinking. Next I think I have to try to work out which 202s propshafts will fit. As you say another option would be to have a new UJ fitted to the existing one. There is a firm in Coventry, 20 miles from me, that offer that service. I have replaced UJs myself many years ago. but I think these days there is no circlip and it needs specialist equipment.