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Old December 27th, 2010, 18:14   #1
Bellyman
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Default Serpentine belt tensioner bounce

Hoping maybe you guys can give me a few clues on this one.

First off, my serpentine belt tensioner is bouncing like crazy when at idle. I'm assuming I need a new alternator pulley.

I get some vibration from it at idle, as expected.

But I seem to be getting a lot of vibration at higher speeds and I was trying to decide if it's related or a separate issue.

New cam went in about 700 miles ago. And it runs smoother than it did before, especially in the 1200 to 1500 rpm range.

The "sound" from the muffler at highway speeds seems to be a nice steady note, just like I would expect, not a "missing" kind of sound.

Acceleration seems to be very good, lots of "umph" when pressing on the go pedal.

Fuel economy seems to be doing about like always, 46 or 47 mpg, which is about what I normally get.

I'm in the middle of a trip and not close to any tools or anyone I know so much more than a cursury glance under the hood is about all that's likely to happen.

I seem to be getting a lot of vibration at engine speeds between about 2000 rpm and maybe 2500 rpm, which seems to work out to the area between 60 and 70 mph. Honestly, the last few hundred miles have felt like I've been riding in a giant orbital sander.

It definitely is tied to engine speed and not vehicle speed. The vibration doesn't go away when letting off the throttle completely but it is made more intense by heavy throttle.

I can understand how the bouncing serpentine belt tensioner can cause some vibration at idle. That's pretty obvious with that thing bouncing like it is. But would that translate to severe vibration at higher speeds?

It seems like if I were having an injector issue, I'd be going through extra fuel. I'm not. If it were a DMF issue, I read a lot about clanks and clunks and rattles, none of which are present. I can hear just a bit of valve noise in the 1500 rpm range but nothing abnormal. There are no warning lights lit on the dash.

I forgot to check backpressure with a hand over the tailpipe but even though it sounds a lot like an exhaust leak, it doesn't let up when letting up on the throttle and I can't recall an exhaust leak causing so much vibration.

Just thought maybe I'd run it past you guys and see if some of you may have already been down this road and found the "aha" moment.

Thanks for any thoughts.

Brian

P.S. It's an '04 TDI Jetta wagon, 5 speed manual, 110,000 miles.
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Old December 27th, 2010, 19:37   #2
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Quote:
I'm in the middle of a trip and not close to any tools or anyone I know so much more than a cursury glance under the hood is about all that's likely to happen.
My first suggestion is out then - starting with a process of elimination.

Since your serp belt tensioner is bouncing, you might want to eliminate that first.

If you had a couple tools with you, I would simply remove the serpentine belt, then take it for a short ride to see if your vibration persists or not.

If the vibration quits, then you know the problem is something in the serp belt path.
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Old December 27th, 2010, 20:04   #3
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Most likely the root of your issue is the alternator Pulley. It has a one way bearing in it that wears out. When I had my issue i replaced the belt, tensioner and pulley. The pulley needs special tools. You should be able to finish your trip. After I noticed i had issues with it i put on nearly 2000 miles before i collected all the parts. The worst thing that could happen for me was to loose a belt.
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Old December 27th, 2010, 21:49   #4
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Quote:
Originally Posted by rentstdi View Post
Most likely the root of your issue is the alternator Pulley.
10x as the hands-down favorite cause of serp bounce at idle.
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Old December 28th, 2010, 01:17   #5
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Thanks, guys. The middle of the trip may find me near a mechanic (with some tools) where I could perhaps get a pulley overnighted in, maybe. (If I do, I'll get a new tensioner, too.)

I'm hesitant to mess with it on the road as long as it's still running. One thing I do like is the fact that the water pump is running off of the timing belt so I potentially have a bit of range should I lose the serpentine belt. Far from ideal, but should be able to limp for a good ways.

I did have a look at the belt path while it was idling at a rest area. I wondered if I could have put the crank pulley on wrong when I did the cam job (had to loosen the timing belt) therefore creating a wobble, but it's turning very smoothly and evenly, not at all wobbling. I'm sure I put it on correctly.

Still wondering what that bouncing tensioner does at high speed but it may have to wait until I get where I'm goin'.

Thanks for the thoughts.

Brian
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Old December 28th, 2010, 04:16   #6
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It's the alternator pulley. Just replace the thing. It's cake on a PD due to where the alternator sits. I wouldn't wait too long as it could possibly throw off the belt, break the tensioner, or worse.
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Old December 28th, 2010, 04:46   #7
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Quote:
Originally Posted by turbocharged798 View Post
It's the alternator pulley. Just replace the thing. It's cake on a PD due to where the alternator sits. I wouldn't wait too long as it could possibly throw off the belt, break the tensioner, or worse.
I agree. If the vibration is EXTREMELY noticeable the alt pulley is on borrowed time. if you can see the belt/tensioner bouncing around at idle, the high speed vibration is just more of the same.

I'd order ahead if you can and have the pulley,tensioner and the special alternator pulley tools waiting for you at your trips midpoint. It's my understanding that these car don't go very far without a functioning alternator.

Temporarily removing the surp belt would be a good trouble shooting step. is your car a PD or an ALH? with the ALH, you would loose the power steering with the surp belt removed.

Good luck.......................
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Old December 28th, 2010, 05:17   #8
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Don't drive the car with a siezed alternator pulley, they can (and often do) break off and tear up ALL KINDS OF THINGS when they do.

Your other vibration might be a DMF, but seriously you need to replace the alternator pulley FIRST.
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Old December 28th, 2010, 05:57   #9
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If your travels take you near a trusted mechanic, contact them. Many of us keep the alternator pulleys on the shelf 'cause we replace a lot of them!
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Old December 28th, 2010, 10:08   #10
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My alternator pulley made a hell of a lot of vibration but not at speed. Usually, mine was just at idle but it was A LOT. Mine was only (I would say) half way seized as I was able to remove the belt and actually get the pulley to spin with some initial persuasion.
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Old December 29th, 2010, 20:19   #11
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Update...

Hope I won't upset too many apple carts by what I'm about to post, but here goes...

I was able to get some garage time with my brother this morning. We did some searching for what might be available for a VW alternator pulley. Closest we could find was $112 at a dealer and we didn't have the tools we needed to change it out. Dealer wanted $150 to change it.

So, my brother remembered a "starter & alternator" shop that's known to be very good that's in this area. His shop (at work, a very large local plant where he's working foreman for a good sized fleet of trucks) uses this shop for a lot of their starter and alternator work.

We pulled the alternator off the car (very easy on an '04 PD) and took it to the place. They didn't have a VW alternator pulley but did have one of the same size & shape that has some flex in it. It doesn't free-wheel in either direction but can move a short rotational distance in either direction. The guys at the alternator shop said that they've been very happy with the way this pulley has dampened serpentine belt vibration. So I bit.

$39. Installed. We set the alternator on their counter, the shop guy picked it and the new pulley off of the counter, disappeared into their shop, and 3 minutes later, reappeared with the new pulley installed.

I was skeptical, but figured it was only $39 and if I didn't like it, I could always change it out at a later time with the VW pulley.

Put it on and started the car up. The tensioner was VERY quiet and barely moved comnpared to the old one bouncing around like crazy. The old one was seeing a rapid fire vibration of what looked like about 3/4 inch of movement. The new one shows something that looks more like about 1/8 inch of movement, if that. I mean, the difference was HUGE!! Way less vibration. And the guys at the alternator shop seemed to think it would be way more reliable than the original.

I dunno if I've "toofed" it or not. But so far, I'm pretty happy with the results.

I haven't had a good road test yet, only a very short jaunt of what ammounts to about 1/2 a block. Tomorrow should give me a chance for a bit more of a run to see.

Another little thing that changing out the alternator pulley fixed was a serpentine belt chirp, which my wife was complaining about. It would often chirp when turning the steering wheel even just a little while anywhere near an idle, which is pretty often when taking off from a stop. Chirp gone. So a happier wife.

Time will tell about vibration at higher speed. I'll update when I learn more.

Just thought you guys would want to know.

Thanks agian for the earlier feedback.

Brian
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Old December 29th, 2010, 20:27   #12
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P.S.

I don't remember the name of the part and I didn't get a part number.

The shop was a Mennonite shop in Denver, PA. It was "Weaver's Repair Shop" but I think they may have changed the name to "Chestnut Hill Auto Electric". They're on Chestnut Hill Rd in Denver, PA.

They appear to really know their stuff, do it well, and are very reasonable in their prices. They're also well respected by a number of local diesel truck service places in the area.

Just in case anyone wants to know.

Oh, I don't think you'll find a website online. But they do have phones.

Brian
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Old December 30th, 2010, 05:08   #13
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They just stuck the low RPM damper pulley on there, many Bosch alternators use them on lower turning engines, like gensets and farm equipment, and it is not suitable for your Volkswagen automobile. My dad's John Deere tractor's Bosch alternator has one.... it's 4cyl turbodiesel engine operates between 1000 RPMs and 2500 RPMs, and does not rapidly change RPMs ever. That pulley is better suited for those.

Usually when people put those on cars, they break apart after a short while. I would get the proper sprag-type pulley. That shop should have known this...
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Old December 30th, 2010, 05:18   #14
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I agree with oilhammer.

IDparts has the pulley for $59

Order one and swap it out as soon as you can.
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Old December 30th, 2010, 05:23   #15
Bellyman
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Oh well... bubble burse once again... (sigh)

Hopefully, it'll at least give me a little less vibration for a week or so while I order the correct parts and tools.

You are right, though. This shop does a LOT of farm and BIG diesel work and those rarely travel beyond 2500 rpm, if they even get that high.

Was hoping I actually found something good. But alas, that proved optomistic.

It's 1000 miles back to home but mostly interstate, which turns out to be mostly 2500 rpm. And with the tensioner much happier, maybe the new pulley will at least give that a better ride home.

Thanks, Oilhammer. I'll fix it right ASAP.

Brian
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