Took out the alternator to check out the pulley today. I was expecting a Valeo but it's a Bosch.
The question: my understanding of the sprag bearing is that when I hold the shaft with a torx bit I should be able to spin the pulley, correct? Mine doesn't budge in either direction. The pulley and shaft move as one.
The VR is also worn, I am gonna weigh the options between replacing VR+pulley vs the whole alternator.
Inputs please!!

 

Just replace the whole thing I assume you have over 100k on the car by now so replace or have it fully rebuilt.
If you search on here there was a discussion about the sprag bearing taking out other components such as ac compressor it will be useful for you.

 

Thx, I am aware of that, spent 5 hours + reading up...I still wanna know if the pulley should move independently of the shaft, for future reference....

 

I am wondering why it is necessary to have a sprag set up. Found this explanation on another site.:-

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Quote:
Originally Posted by maschwar
Not the news I wanted but thanks. I will do that.
Can anyone explain why the alternator has a clutched pulley?

To prevent excessive belt flapping. Every time a cylinder is compressing, the crankshaft slows down. Every time a cylinder fires, the crankshaft accelerates, even at a constant RPM. Especially when there is high load but in the diesel, even more than any gasoline engine.

Since drive belts can only "pull", the belt also speeds up and slows down which creates vibration on the tensioner. Since the alternator has the smallest pulley, it sees the most from these accelerations and provides the most rotational inertia. With the sprag clutch locked, when the engine slows down, it now PULLS the belt from the tensioner, making the other normally tensioned side slack! And it pulls the tensioner up.

When your sprag clutch locked up, it caused the tensioner to vibrate far more than design limits of the damper, placing a great load on the mounts which caused the mount to break as it is cast aluminum which doesn't have an endurance limit. VW engineered this part for high cycle life with normal operation. When the sprag clutch failed, the applied stresses were far in excess of low cycle fatigue.

So, the answer why VW uses a sprag clutched alternator? Noise, vibration and harshness. And you need to replace BOTH the clutched pulley and the tensioner. Sorry.

This is the same reason for the dual mass, damped flywheel. "

 

Heading over to oreilly auto parts, they have a couple in stock.....easy way to find out.

 

https://mbworld.org/forums/5828264-post22.html

How the pulley should behave:
https://mbworld.org/forums/5821320-post14.html

 

Thanks VVF, also confirmed it at the parts store. Reman unit on order.

 

Excellent Info . Thanks VVF

 

Just changed out the alternator, engine is suddenly WAAAY quieter! I guess the seized pulley was causing the belt to slap around or something. I was on the verge of buying a $400 PS pump coz I was sure that was the culprit! Cold and warm start idle rock steady.
On a side note, just dropped the car off at the stealer for the cam solenoids, they found oil in the harness and and putting in a new one. They even gave me a ride home, said they'll call and pick me up when it's ready! Great folks at MB of North Houston

 

Those great folks once charged me for the pigtails for the solenoids but "forgot" to install them... Although the manager admitted SA's fault.

I guess you may also need to change the belt, idler and tensioner pulleys because they may have sustained some wear.

 

Yup....belt sitting in the trunk, idler and tensioner pulleys arrive Thursday. My other ride is a 5 spd e46 3 series, I'm finding that I tend to want to drive the c more....

 

.... Really? No way!