Auxillary drive belt noise and vibration

[superdunx]

Hi group,

I wonder if anyone can help with a problem I have. The car is a 2000 registered W202 shape C220 cdi. The problem that I have is that on idle the top of the auxillary drive belt (between the power steering pump and the idler pulley on the water pump) vibrates and makes a brrrr noise. (best description I can come up with!) This is also very noticable when you take up drive whilst pullling away from standstill. The noise and vibration goes away when the engine is running at a speed greater than idle.

So far I have changed the belt and tensioner, inspected all pulleys for damage and rotated each by hand to ensure they are not stiff or binding. Everything seems to be as it should.

Then by chance, a discussion with an ex MB mechanic. He said it may be a freewheel pulley that they fitted to the alternator. Apparently they fitted this on later cars to avoid this very problem (due to the inertia of the alternator when it is not loaded) Whilst I didn't believe him at the time, the problem does go away when the alternator is under a heavy load. Anyway my local MB dealer say they know nothing about any of this and want to charge £90 per hour to FIND the problem let alone actually fix it when they do find it.

Has anyone else had a similar problem and may be able to point me to a cause? Does anyone know anything more about the freewheel pulley or may be able to point me to some information about this.

Many thanks in advance,
Duncan.

 

[andrew_eales]

Hi

I presently have the same issue with my 2001 W203 220 CDI.. I have had a new belt tensioner fitted with belt, but I still go the same noise. I would have you intercooler checked, as if this is damaged it will make the engine shake as there is a lack of air, mine was and the new one has helped.

I went to a MB dealer who told me that it was my injectors and alternator, I worked out that this would have cost me £2000!!!!!!!. I have since done some more investigation and found that it could be the guide pulley for the water pump, which although is spinning, may be warped which is causing friction on the belt, making the rough idle. I hope it is, this as my local man will be much less than the Merc bill, which would not have made any difference.

Regards Andrew

 

[tamrsoft]

Drive Belt Vibration

There is a classic fault that occurs on the 220 CDi engine (as reported by MB)
regarding excessive drive belt vibration which affects idle (very pronounced on initial startup). It is caused by the alternator drive pulley, not the tensioner. The drive pulley contains a freewheel clutch within it and its this clutch that has a very common habit of seizing up. It's easy to check, remove the plastic end cap on the pulley and check that you have a multisplined aperature in the end, this identifies the freewheel pulley. Now turn the pulley CCW, the shaft should not turn then turn CW and the shaft should turn. If it turns in both directions, the pulley has seized. It needs the special multisplined tool to remove and I believe it is about £90 + labour to replace. It can also retro-fitted to earlier engines that did not have it.

 

[tamrsoft]

Forgot to mention, remove drive belt first, this is also very easy as it is a pre-tensioned tensioner and only requires a 17mm socket and long'ish bar to ease the tension