replaced alternator, now have strange vibration at idle

Last week I replaced the alternator with a Bosch 120amp unit. Car is 2002 with ALH motor and 5-spd tranny. The new alternator is putting out over 14 VDC at idle but there is a vibration now that wasnt there before. Once car is revved above idle or when I am driving, the vibration goes away. When I first started it up after the alt replace, I noticed the bolt holding the damper on the tensioner was a little loose, so I tightened it but still didnt fix vibration. Anybody ever had similar issue?

Followed Wingnut's how-to for the ALT replacement, GREAT write-up! Many thanks!

Where did you get the alternator ?

In case you didn't know, TDI alternators have a clutch in the hub. This allows the alternator to freewheel. Diesels have strong rotational pulses during the power stroke, this can cause problems with the tensioner and belt. Could be you have a bad clutch or you got the wrong alternator.

Is your tensioner jumping around ?

+1 on alternator clutch

I got the alternator at a local advance auto. I have tried to confirm it is the same part number as listed on several of these forums, Bosch AL0189X, and unable to do so, only that it is a Bosch part. I do remember before the install I was able to turn the alternator shaft both ways. Does this indicate a bad clutch, or even no clutch at all? Would it be best to see about returning this unit and getting the right part number alternator?

Thank you for the advice!

If you were able to turn the alternator armature both ways, you probably installed the wrong alternator.

One direction should have freewheeled.

Best bet is to see if advance auto will give you a refund and get a replacement alternator from one of the authorized vendors on this forum, like below.

http://www.idparts.com/catalog/product_info.php?cPath=123_129&products_id=3919

http://shopping.boraparts.com/product_info.php?cPath=21_26_34_63&products_id=1073

You might be able to buy and install a clutch hub while its installed, not sure if it would be worth it or if you have the right alternator. There is a special tool sold for this.

http://www.idparts.com/catalog/product_info.php?cPath=123_129&products_id=1118

http://www.idparts.com/catalog/product_info.php?cPath=123_129&products_id=564

To check the clutch pulley, remove the belt, block the alternators internal fan and try to turn the pulley both ways. It should turn smoothly in one direction and not turn in the other direction.

Ol'Rattler said:

To check the clutch pulley, remove the belt, block the alternators internal fan and try to turn the pulley both ways. It should turn smoothly in one direction and not turn in the other direction.

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Thanks, that's the correct method, hard to tell otherwise, especially in the car.

Do this before you conclude its the wrong alternator.

To check Alternator Pulley you do not need to remove anything.
All you need to do put your finger inside alternator and move impellers(Cooling Fan) clock wise , if they not moving then alternator pulley is bad.

Also if you have solid Pulley toy will see that very easy.

Got the belt off, blocked the internal fan and the pulley turns counter-clockwise (looking at pulley from passenger side of car) smoothly and not at all clockwise. Does that rule out any clutch problem or incorrect alternator?

The pulley is probably OK then. Next thing to try would be to remove the belt completely and run the engine. That would at least narrow it down to something that is turned by the serpentine belt.

From what you said about the vibration not being there before, and even though the Pulley is good, I would suspect the alternator. Was it a re-man or new? Probably time to take it back and tell them it's defective because of the vibration.

jetta said:

To check Alternator Pulley you do not need to remove anything.
All you need to do put your finger inside alternator and move impellers(Cooling Fan) clock wise , if they not moving then alternator pulley is bad.

Also if you have solid Pulley toy will see that very easy.

Click to expand...

Not a bad idea although with the tension on the belt, the fan might be hard to turn in the freewheel direction with your finger. Certainly worth a try.

Ran the engine with serpentine belt completely off, no unusual vibration. It was definitely coming from something being turned by the belt. This was a re-man unit. Going to order one off idparts.com and return this one to advance auto.

Thanks again for the help!

Ol'Rattler said:

Not a bad idea although with the tension on the belt, the fan might be hard to turn in the freewheel direction with your finger. Certainly worth a try.

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This how I check them and it takes less then 1 min.It will turn very free with belt on it.

Better to get the OEM as they are hard to change on an alh.

d2305 said:

Better to get the OEM as they are hard to change on an alh.

Click to expand...

Jetta is much easy compare to New Beetle.

jetta said:

This how I check them and it takes less then 1 min.It will turn very free with belt on it.

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Well sir, your technique for checking the clutched pulley is going into my "bag of tricks" then...........

Golfer49 said:

Ran the engine with serpentine belt completely off, no unusual vibration. It was definitely coming from something being turned by the belt. This was a re-man unit. Going to order one off idparts.com and return this one to advance auto.

Thanks again for the help!

Click to expand...

Seriously, The only thing I buy at the local parts houses is car wash stuff head lights and candy bars. Re-man anything from those places can really be a crap shoot.