7 replies to this topic

[Wayne & Tru]

I have a 2006 Freightliner M2 Business Class truck with a 260 Mercedes engine.

The fan belt squeels like it is loose but it is not. It is so loud going down the road I can hear it in the cab.
A new belt quiets it for a few hundred miles then it comes back.
I have replaced the tension pully and the crankshaft damper/pulley to no avail.
Belt dressing makes it worse.

Any ideas?

[Stanley P. Miller]

Have you checked the belt tension spring? If it is weak it can cause problems.

Have you looked for a bent (wobbling) pulley?

Have you tried spinning all the belt driven stuff by hand and made sure it is spinning freely?

Does it squeal if you just run the RPMs up in neutral?

[SIBERNUT]

The belt does not drive by being "tight" alone. It sounds like it is bottoming in the pulleys, which is only a small contact area. It should drive by "wedging" down and the sides touching the pulley sheave. Are you using the factory spec belt, or just matching what's on there? Belts are made in different widths, it sounds like yours is too narrow.

[Wayne & Tru]

Thanks guys,

I will try to answer all your questions.

First, the tension spring was replaced with the tension pulley. The belt is very tight.
Second, there are no wobbling of any pulleys.
Third, the two tension and idler pulleys have some tension which the truck maintenance persion I took the truck to said was normal.
Fourth, the squeel gets worse when you turn on the a/c or run up the rpm's.
Last item, the belts all have come from Freightliner using my vin number to get the part number for the belts.
I talked to the Freightliner parts rep and he was also puzzled.

The only thing that my tech was concerned with is that the belt only contacts the crankshaft pulley about one quarter of way around the pulley.
With all that the belt is turning, the belt apparently slips a little. This is a design problem.

Thanks again for your input.
Any other ideas.

[SIBERNUT]

My prior reply was for a V belt. If you have a serp belt, check the routing. Sometimes a belt will go around pulleys several ways, but only one is correct.

[Stanley P. Miller]

The flat belts usually don't have a squeal problem if tensioned properly and none of the accessories are dragging. The low contact area might well be the problem and could be compounded by the tension roller being on the light end of the allowable range which doesn't seem to be your situation.

A search of the FL database might turn up a recall or service bulletin if you can get someone to spend the time on it. If you can't do that you might get your dealer to escalate the problem but that might take a while and you'd need to be near the dealer if they need to look at things in more detail for the support reps.

Something you could try is removing any glaze on the pulleys, it can be removed with a ScotchBrite pad and a bit of alcohol being careful to not get the alcohol on the belt. If you used belt-dressing meant for V belts it might be causing slipping, a good hot-soapy scrub might help to remove any of that if it is on the new belts.

Google was no help in finding anything specific to your truck / engine combination.

[Wayne & Tru]

Thanks again,

It is a serpentine belt and there are no arrows on it to say it is supposed to travel only one way.

My tech is checking with FL but I was hoping the someone here might have run into the same thing.

The belt dressing I bought from O'Reilly auto parts doesn't say it is only for V belts. It is a clear spray.

Thanks again

[ctooraen]

Sure the ac compressor is not locked up? I would certainly recheck the routing of the belt. Does the belt look chewed up or abnormally worn after some miles?