VW Passat alternator belt just snapped for 2nd time

VW Passat alternator belt just snapped for 2nd time

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Discussion

jsmithakawilliam

Original Poster:

5 posts

84 months

Monday 20th March 2017
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My VW Passat alternator belt just snapped for 2nd time within a few months, with catastrophic effect ( took out timing belt and we all know what happens when that occurs !!!! ).

Has anyone else had this issue ?


TimmyMallett

2,811 posts

111 months

Monday 20th March 2017
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That would suggest there is a root cause somewhere that caused the first to snap as well, as opposed to just wear. Bearing somewhere in the run that is causing the belt to be out of alignment and rip?

cptsideways

13,535 posts

251 months

Monday 20th March 2017
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Alternator clutch pulley fobarred

Rich_W

12,548 posts

211 months

Tuesday 21st March 2017
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cptsideways said:
Alternator clutch pulley fobarred
This! It amazes me that so many garages (indy and dealer) never check this after the first failure (or belt getting noisy at full lock)

jsmithakawilliam

Original Poster:

5 posts

84 months

Wednesday 22nd March 2017
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If fobared the same as Fubar-ed ?

I'll mention it to the garage thanks.

There must be more too it that they're not letting on about.




SuperchargedVR6

3,138 posts

219 months

Wednesday 22nd March 2017
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There's 3 reasons why a serpentine belt would snap.

1) Wrong type or size fitted, or not aligned properly on the pulley grooves.

2) Seized tensioner pulley, but you would get an awful screeching racket to go with it.

3) Seized clutch in the alternator pulley, which is not obvious to most end users except when letting off the gas at high revs, but that's not applicable to diesels as they can't do revs :-)

The idea of the pulley clutch is to allow the alternator to 'free wheel' when the engine isn't accelerating. Modern alternators produce massive current and therefore need lots of (heavy) windings. These windings have substantial rotating mass which if not kept in check, can cause the belt to jump off, stretch, over heat, wear out.....etc.

It's easy to check. Relieve tension on the belt by putting a 15mm spanner on the belt tensioner and push it until the belt is loose. Now spin the alternator clockwise then quickly try and turn it counter-clockwise. You should feel the clutch free wheeling when counter clockwising it. If you feel the alternator turning in both directions, the pulley needs replacing.

annodomini2

6,860 posts

250 months

Thursday 23rd March 2017
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SuperchargedVR6 said:
The idea of the pulley clutch is to allow the alternator to 'free wheel' when the engine isn't accelerating. Modern alternators produce massive current and therefore need lots of (heavy) windings. These windings have substantial rotating mass which if not kept in check, can cause the belt to jump off, stretch, over heat, wear out.....etc.
Other way around, they disable the alternator under heavy acceleration to free up a couple of bhp when accelerating.

They can also save emissions when it's not needed, e.g. battery >95%, low electrical load etc

SuperchargedVR6

3,138 posts

219 months

Thursday 23rd March 2017
quotequote all
annodomini2 said:
SuperchargedVR6 said:
The idea of the pulley clutch is to allow the alternator to 'free wheel' when the engine isn't accelerating. Modern alternators produce massive current and therefore need lots of (heavy) windings. These windings have substantial rotating mass which if not kept in check, can cause the belt to jump off, stretch, over heat, wear out.....etc.
Other way around, they disable the alternator under heavy acceleration to free up a couple of bhp when accelerating.

They can also save emissions when it's not needed, e.g. battery >95%, low electrical load etc
That would imply some kind of electronic actuator? I'm talking about the one way pullies. Like a rear sprocket cluster on a push bike.

annodomini2

6,860 posts

250 months

Monday 27th March 2017
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SuperchargedVR6 said:
annodomini2 said:
SuperchargedVR6 said:
The idea of the pulley clutch is to allow the alternator to 'free wheel' when the engine isn't accelerating. Modern alternators produce massive current and therefore need lots of (heavy) windings. These windings have substantial rotating mass which if not kept in check, can cause the belt to jump off, stretch, over heat, wear out.....etc.
Other way around, they disable the alternator under heavy acceleration to free up a couple of bhp when accelerating.

They can also save emissions when it's not needed, e.g. battery >95%, low electrical load etc
That would imply some kind of electronic actuator? I'm talking about the one way pullies. Like a rear sprocket cluster on a push bike.
2 Different systems apparently:

http://www.pistonheads.com/gassing/topic.asp?t=127...

Stand corrected

SuperchargedVR6

3,138 posts

219 months

Wednesday 29th March 2017
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annodomini2 said:
SuperchargedVR6 said:
annodomini2 said:
SuperchargedVR6 said:
The idea of the pulley clutch is to allow the alternator to 'free wheel' when the engine isn't accelerating. Modern alternators produce massive current and therefore need lots of (heavy) windings. These windings have substantial rotating mass which if not kept in check, can cause the belt to jump off, stretch, over heat, wear out.....etc.
Other way around, they disable the alternator under heavy acceleration to free up a couple of bhp when accelerating.

They can also save emissions when it's not needed, e.g. battery >95%, low electrical load etc
That would imply some kind of electronic actuator? I'm talking about the one way pullies. Like a rear sprocket cluster on a push bike.
2 Different systems apparently:

http://www.pistonheads.com/gassing/topic.asp?t=127...

Stand corrected
Yeah 'Max Torque's explanation (number 1) was how I understood the 'freewheeling' pullies. I also see I commented in that thread. Where the hell have 4 years gone?!!