Serpentine Belt Tensioner

2004 Passat with 193,000 miles. Recently had timing belt and all that stuff done.

Also had to replace the serpentine belt tensioner because it was making a terrible racket and belt would squeal when turning at low speed (e.g., parking lot).

New tensioner was quiet for a few days, then the belt started squealing again but NOWHERE near as bad as it had been.

Took it back and for various reasons just tried replacing belt - tensioner seems tight, but how can you tell without doing some kind of test on the spring? How much does it need to be out of spec to be a problem? Anyway - it was quiet for a few days and started squealing again - but not nearly as bad as original problem?

The only thing I can think to do is replace the tensioner again, but the shop said they had another like mine that still squealed after a new tensioner. BTW - this is not a dealer, this is a respected VW dedicated mechanic who has had his shop in the same place since 1975....

Now What? Anyone else had a problem like this?

Hey, I get to be the first to say it - it's your alternator pulley.

How would the alternator pulley cause the serpentine belt to squeal when the power steering pump is causing a load (i.e., turning at slow speed)?

Search for it, tons of posts in this forum about it although I haven't seen a new one in a while. Basically the pulley on our alternator needs to freewheel and when that clutch breaks it can't do that anymore, putting all kinds of stress on your nice brand new tensioner, causing it to not do its job well and thus the squealing. Either that or your power steering is trying to pull more from the serpentine and since it can't freewheel around the alternator pulley there's some squealing going on.

Apparently a freewheeling alternator pulley is not a common thing so don't be surprised if your mechanic looks at you funny. And just getting a new alternator won't necessarily fix things - because it may come with the wrong pulley.

Same thing happened to me a few years back and the highly-regarded indie VW shop I took it to replaced my serp tensioner - that lasted an afternoon. Then they replaced it with an OEM tensioner and that lasted a day. I finally did my own research on this forum and found the answer. Haven't had a problem since.

Here you go, I'm avoiding my homework.

http://forums.tdiclub.com/showthread.php?t=364336

Thanks for the link - I'll check it out.

The tensioner did need to be replaced as it was REALLY bad with the noise and it was visibly bouncing around. Now, it may be that the reason the tensioner went bad was because the alternator pulley is bad....

ludwigmace said:

Hey, I get to be the first to say it - it's your alternator pulley.

Click to expand...

Hey watch it buddy, I'm the guru in this here town

Keith J. Barton said:

it may be that the reason the tensioner went bad was because the alternator pulley is bad....

Click to expand...

Roger that.

Keith,
I had the same issue. Loud squealing belt sound. And the belt was flopping around. New belt didnt solve it. A shop wanted to change the Tensioner for big bucks, but I did some forum reasearch in here first. Then I changed out the Alternator Pulley (it's an updated Part number too I believe) and all was well. The Alt Pulley is a one way pulley or something ( I forgot why) , and when it goes bad it manifests itself in strange ways, like a squeling bouncing belt.
There's a great write up on how to change out the alt pulley somewhere on here.

Dan

There is a sprag clutch/bearing inside the pulley.
It is like a mechanical diode that lets things turn one way but freewheel the other.
They are very common in a lot of applications like automatic transmissions or starter drives.
A diesel has a couple of things going on that is different from a gasser
#1 when you shut it off it stops so quick that the momentem of the rotor in the alternator wants to keep it spinning so it will give a short sqeek from the belt.
The famous sqeek when someone is shutting off a Dodge diesel truck.
So the trick was in that case to add the sprag clutch/bearing to the alternator pully to let the alternator rotor to keep on spinning for a couple of seconds when the engine stops.
#2 the little 4 cylinder diesel in our Passat has a pulse effect on the crankshaft far more than most engines.
Even though your tach will read a steady 850 rpm the crank is going for a split second faster than that when a cylinder fires and slower than that on a compression stroke.
With an ordinary pully or a failed sprag in a pully this effect jerks back and forth on the serpentine belt because the alternator rotor with its rotating mass does not want or like to speed up and slow down like the crank is doing that quickly.
So about 425 times a minute the little clutch in the pully is going to grab and release in normal operation to make the belt run smooth and not sqeek when you shut the diesel off.
If that helps!

Actually, for the record, one-way alternator clutch pulleys ARE a common thing. Nissan, Toyota, GM, Chrysler, BMW, MB, just to name a few, all have them.

So if your mechanic looks at you funny, he's an idiot.

Actually, for the record, one-way alternator clutch pulleys ARE a common thing. Nissan, Toyota, GM, Chrysler, BMW, MB, just to name a few, all have them.

So if your mechanic looks at you funny, he's behind the times

The alternator pulley was it. All works well again. Even without the belt squealing it was making a racket. I was concerned the balance shaft drive chain was going (194,000 miles and still as it was from the factory) because of the noise. I'm no longer worried about the bs chain.

You probably should be

Oh, I know I should be, but I can't afford to be worried about it right now - much better for me to pretend all is well: that job is too big for me and I can't pay for the parts or labor anytime soon....

glad i found this thread!

just started noticing the same squeaking, which doesn't necessarily go awhile while driving or revving the engine. don't know how long it's been doing it because i can't hear it unless i'm outside the car or have the windows down.

this also makes total sense why the traction control light would come on when first starting the car when it was cold this winter. thanks to this forum, found it was due to low voltage output. tying it together with this thread, it seems like it's due to the alternator pulley.

ordering the alternator pulley and tools from metalnerd today.

once again, a big thanks to everyone on the forum.

I have a regular pulley on my alrernator and it doesn't make any noise ever. The theory of it needs to freewheel or else it makes noise is not true. The siezed pulley is doing something else to make the belt squeel.

imo000 said:

i have a regular pulley on my alrernator and it doesn't make any noise ever. The theory of it needs to freewheel or else it makes noise is not true. The siezed pulley is doing something else to make the belt squeel.

Click to expand...

bs ^^^

Yeah, I don't believe it either. Not that it doesn't make a squeal, but that it doesn't hammer on the belt and tensioner. Because I've seen too many of these things like that.

This is on my Jetta. Shouldn't matter that much because the principal is the same. Don't be so quick calling BS. It has been on the car for some time and nothing has come loose.

My B4/1Z passat had a solid pulley when I got it, but I can't say if some previous wrench changed it out.

I did swap in a clutched pulley soon after I got it though. Factory or not, the belt chatters nicely without it.

just order the tool from metalnerd.

what is the best source for the alternator pulley?

Boraparts and IDparts carry them. Bora has free shipping....

INA Overrunning Alternator Pulley

The INA Overrunning Alternator Pulley (OAP) is an auxiliary drive solution that, in contrast to a solid pulley, allows rotational motion in order to dampen vibrations. For what this means exactly, watch here….

http://www.schaeffler-aftermarket.u...athek/videostore/video-details.jsp?id=3540995



.

Pretty much every manufacturer is using these nowadays.

Yup. Just replaced a pulley on my wife's 4 banger Altima. It was making a sound like a bad bearing. Replaced the pulley and the noise was gone. Also had the pulley separate on my ALH in Virginia 3 years ago.

I now understand the theory of why they want to use them. I disagree that they were necessary. What did we ever do the previous 100 years before clutched alternator pulleys?

Wish I could have had one on my old SHO. I recall hearing the belt chirp if I let off the throttle up near redline and the autotragic tranmission upshifted and dropped the rpm from 7000 to 2000 rpm or less.

And bigger, slower spinning alternators that put out less power. We also had these awful things called 'V-belts', many of which required the whole alternator to move in order to tighten them. Boy, the newer cars' accessory belt drive systems are many light years better than they used to be.

oilhammer said:

...We also had these awful things called 'V-belts', many of which required the whole alternator to move in order to tighten them...

Click to expand...

Wow, does that bring back some old nightmares, or what?

1854sailor said:

Wow, does that bring back some old nightmares, or what?

Click to expand...

Sadly, I still own some of those cars... and they are all diesels. Which means, I get to check/adjust/tighten/replace a lot of belts. I'm going on 90k miles on my ALH post untooefing,, and I don't think I've so much as glanced at the accessory belt in that time.

The Dodge/Cummins used that Sprague clutch on the alternator for a different reason.
On these the engine would stop so quick on shutdown that the spinning mass of the alternator would make a loud squeak from the belt!
Mine never got the upgrade and belt is still just fine after 126k miles
Being a larger 6 cylinder with a much larger flywheel it doesn't play havoc with the tensioner idler like the little 4 bangers do!