Mystery noisy bouncing aux belt & tensioner on c220 cdi w203

[Graham.]

Hello. Thanks in advance for any help with this problem thats driving me potty.
Tried some new parts. Problem persists.
On tickover my engine is noisy with a booming rattle. As soon as you bring it above tickover it runs smoothly. On full lock it chirps. Under the bonnet I can see the serpentine aux belt vibrating and bouncing across its widest span at the top. Also the tensioner vibrating horizontally.
I have replaced the belt. No change. Then replaced the tensioner. No change. Then tried a genuine mb belt. No change. And now a genuine mb tensioner and still no change. All the pullys seem to run straight and true. They all spin freely when the belt is off and I cant detect any free play in any of them.
The alternator pully spins in both directions.

Any help and suggestions as to what can be causing this would be greatly appreciated.
Thanks, Graham

 

[142 TPL]

This is your alternator pulley. It has a freewheeling pulley and it is seized. Just change that and the difference will be unbelievable.

 

[Ian B Walker]

It could also be the crankshaft pulley. They are bonded onto the centre hub with rubber. This can deteriorate and cause the crankshaft pulley to oscillate.

 

[tul214]

Gents,

I know this is an old thread but I have the same symptoms as Graham.

I have replaced the water pump because it had a bit of play in it but the problem persists.

Any other ideas?

Thanks Mark.

 

[tul214]

OK, i tried to lock off the alternator and turn the pulley......solid both ways so it looks like the pulley is shot.

Is it possible to remove the pulley in situ?

 

[Auto-mobile]

Yes but you need the tool to do it.

 

[tul214]

Thanks, are all the tools the same, i.e. M10 torx and 33 spline?

 

[Danny DeVito]

Pulley gone. Look up the numbers and find the appropriate tool

 

[tul214]

As per the comments above.....new pulley and its gone quiet again