Somehow I missed out on the service campaign to replace the harmonic balancer on my 1998 ML320 with 94,000 miles. Two dealerships in the past few years never informed me and I did not get a mailing from MB.

So here is what happened. I was at a signal an noticed a big truck next to me and thought; Wow, that sure is one noisy truck. The signal changed and the truck went away and the noise was still there and it was coming from my ML320. Once I started to pull forward I noticed that I did not have power steering and the battery charge light went on.

I pulled into a parking lot and looked under the hood. The belt had no tension.

Fast forward.

Towing Charge - $180
Repair Charge - $644

The dealer replaced a "broken" harmonic balancer under the service campaign and charged me for a belt tensioner, belt & cooling block cover seals.

The dealer now says that the balancer was only cracked and that the lack of power steering was related to the belt tensioner failure and has rejected a request to pay for the towing charge. They also reject any reimbursement for any of the other repairs.

Since the loud metal on metal grinding noise continued even when there was no tension on the belt, I think that the sound was coming from the harmonic balancer. If the belt was loose it could not have been turning the belt tensioner and causing it to make so much noise.

My questions:

1. Could a failure of the harmonic balancer have caused the belt tensioner to fail?
2. Could a failure of the harmonic balancer have caused the oil leaks in the cooling block covers?
3. Or is it just a coincidence that the belt tensioner and oil leak starts at the same time as a "crack" in the harmonic balancer?

Your ideas on my problem would be appreciated.

in Hawaii

If the tentioner was the issue, getting a free balancer was about all MB accepts responsibility for. If they combined fixing the leaks (which probably have been there) you might have saved some labor having them done at the same time. It is logical for them to find these other problems while working in this area. The balancer would have only been the problem if it had come apart. The cracks would only be a warning if caught in time.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,

Thanks for your comments. Do you think that the very loud noise could have been coming from the harmonic balancer if it was only cracked? Or is it more likely that it broke apart at caused the tension to go out of the belt?

A cracked balancer would not have caused any problems. Based on the explanation the tentioner came apart. The balancer also comes apart and causes all kinds of problems, but it has to come apart to cause them.

If the balancer did not come apart it sounds to me like the tech did a thorough job repairing the damage and noticing other issues in the area.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve and anyone else,

I am not sure if the dealer is telling the truth about the condition of the harmonic balancer. At first it was said to be broken and then when they denied the towing charges they said it was cracked.

1. Would a "cracked" harmonic balancer cause the belt to lose tension?
2. Or, does the harmonic balancer need to "break" in order to create a loud noise and cause the belt to become loose?

It seems logical that if there just a bad tensioner the belt would have become loose and the battery light would have gone on. The loud noise cannot be explained to me by just a bad tensioner. Can anyone shed some light on this subject

A cracked balancer would not be noticed unless you looked at it. IT WOULD NOT cause noise or lack of belt tention. It would have to come apart to do that. If it is cracked it will probably come apart soon and reek any manner of havoc, but it has to come apart to do that.

The tentioner is a drum on a bearing the belt rides over. It also is spring tentioned into the belt. It does come apart and make a bunch of noise and the belt just hangs there.

I wasn't there so I can't tell you what happened. The story you heard is entirely plausible. Without any evidence to the contrary, I'd believe them and go on with your life.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I would call " C.S.I. " Mercedes-Benz and ask them to investigate.

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2007 C 230 Sport.

Lanikai, too bad you didn't ask the MB dealer for the damaged harmonic balancer. I've learned to request old parts when expensive repairs are involved ... or at least the opportunity to examine the old parts so I get a clear understanding of why the repairs are necessary. It seems odd to me that a belt tensioner would fail suddenly without some prior 'warning sounds' or 'strange noises' under the hood for days/weeks/months.

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Fred Hoelzle

Thanks guys for your responses. Since I live in Hawaii I thought of getting Charlie Chan on the case. Alas the physical evidence has been misplaced and we will need to build our case on circumstantial evidence alone.

From your input and with a bit of logic, this is what I figured happened.

While pulling up to the signal there was a sudden and very loud noise. It was not until the signal turned green that it became apparent that it was not the truck next to me but my 10 year old ML 320. As I pulled away from the signal I realized that I had no power steering and the battery light was on.

Something did not seem right when the story from the dealer changed. At first the harmonic balancer was "broken" and then when they wanted to deny my request for towing reimbursement it was "cracked".

"Suspicion is the father of truth"
Charlie Chan
Charlie Chan at the Race Track (1936)

If it had been just a cracked harmonic balancer, Steve with 33 years of experience tells us that there would not have been a lot of noise and lose of belt tension.

So, you say it must have been the belt tensioner that broke at the traffic signal. This is what the dealer would have me believe.

"Hasty conclusion like gunpowder. Easy to explode."
Charlie Chan
Charlie Chan in Paris (1935)

The key observation is that the sound continued after I pulled into the parking lot. When I opened the hood the belt was not turning yet there was still a loud noise.

If the belt tensioner had been the cause of the loose belt, then where did the loud noise come from? I could understand that a bad bearing in the belt tensioner could create some noise, but since the belt was not tight the bearing in the tensioner was not turning, the belt tensioner could not have been the source of the loud noise.

"Truth, like oil, will in time rise to surface."
Charlie Chan
Charlie Chan's Murder Cruise (1940)

The loud noise must have been coming from the "broken" harmonic balancer. The fact that I had little collateral damage when it broke is probably due to the low engine speed as I pulled up the the traffic signal.

The dealer should reimburse me for the cost of:

1. The towing since the harmonic balancer failure was under a service campaign and
2. The new belt since it very likely to have been damaged by the harmonic balancer failure.

I will never know if the belt tensioner needed to be replaced but I am sure that it was not the cause of the emergency tow that balmy Friday night in Hawaii.

Aloha,

If the harmonic balancer did break, you would have incurred much worst damage, e.g. timing cover, radiator, just to name a few. The harmonic balancer is spinnng with your engine (whatever speed that was) and when it breaks, you don't want to be in its way. It looks like your harmonic balancer did not break and your dealer just did you a favour by replacing it and claimed it under the service campaign. You should have thanked the technician for a thorough job.
If the tensioner broke, on the other hand, your belt won't be turning. As a result, it won't drive your power steering pump, won't drive the alternator, hence the battery lite came on. If the tensioner was never replaced, it is very well possible that it is the culprit.

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98 ML320 (gone but not forgotten)

I agree with Supradupe. I had a balancer fail and the damage was many THOUSANDS of $$....closer to $4,000 than $2,000. After a fight, we worked it out and after the recall, I eventually recovered ALL my expense.

The tensioner operates somewhat independently of the balancer. If the tensioner fails (not an uncommon event), there's no tension on the belt, regardless of the balancer condition.

For my experience, once the balancer failed, it tore into the timing cover. It never leaked because I shut engine down as soon as it failed. But the cover was severly scored and I suspect would have leaked in a matter of minutes. In my opinion, I don't think a balancer failure will be the cause of a tensioner failure.

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Jim