old98

I started hearing a small rattle a couple of months ago when I was stopped with the car in gear, if you put it in park it would go away, now it is all the time and seems to be getting worse, I have tried to locate it and when I relieve some of the tension off of the belt tensioner the noise goes away, the bearing seams to be OK in the tensioner, could it be the harmonic balancer? I have 157K on it. I live far away from a dealer and would like some advice before I spend a day going to the dealer.

nsfkid

It is most likely the tensioner, Look at it with the engine running. If it is jumping around that is your problem. the bearings rarely go on them. There is an updated tensioner now.

As for your harmonic balancer with the engine off take a close look at it, the out and inner metal parts are connected with a thin layer of rubber that fails and separates or becomes off center. you can normaly tell by looking at it.

My moneys on the tensioner. It is an easy job to do yourself in less than an hour with basic hand tools. (I did mine about 4 months ago my ml has 117K kms on it)
Use a new belt if you change the tensioner.
I drove mine for about a month with tensioner going, sounds nasty, was embarassing to drive
Mike

Let me know what it turns out to be.

old98

I am almost sure you are right, my thoughts was I would replace it, I was thinking it would be $100 or less, This parts guy takes care of me so I don't think he was jacking the price up, just wondered if this was about what yours cost.
Thanks

nsfkid

I got lucky, I bought one from a guy on Ebay who seems to work at a MB dealer new in box genuine MB part.
I think paid about $120 U.S. Here in Canada MB list is $264 CAD about $240 U.S.
It is an expensive part, I do not think it is available aftermarket. O.E is the only why to go for this part

The original tensioners have a metal pully, the updated ones have a plastic pulley.
Mike

I normally get a 15% discount from MB on parts, If I get lucky 20%
They don't give discounts easily.

sosh

Balancers generally do not rattle before a complete failure. My thought is one or more bad CATs. They typically rattle due to broken internals. There is a recall on them for this very problem and you may be eligable for free replacement. Visit a dealer.

VTBenZO

I just had the same problem, it is the CATS, I heard the rattle while on drive but it went away while in park. There is a recall,my dealer does not stock them, so CATS on order, no charge, covered.

old98

I am going to replace the tensioner, I had decided there was nothing wrong with the balancer, the noise is in the front of the engine, relieving belt tension makes the noise go away. The converters do not seem to be rattling, but I think I will see about warrenty on them. It will be the first of the week before I get to it. I will post result, if I wasted money or not. Thanks for the help. Now to the tranny cable leak.

old98

NSFKID, you were right, I gambled with the $192 tensioner (MB dealer)and it fixed my rattle, the new one was a update I believe it looked a little different and had a place you could use a 16mm socket to use as leverage to loosen the belt when needed. It took about 30-40 mitutes to change.