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Discussion Starter #1
When my T4 is idling and I turn on the lights there is a vibration sound which seems to be coming from deep within the engine.

I'm thinking the alternator is on its way out or something is loose in it causing it to rumble/vibrate when a load comes on it.

Anyone else have similar issues?
 

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May have to "eat my hat" here :eek:
(http://www.vwt4forum.co.uk/showthread.php?t=861730)

Normally, only time an alternator will make a "rumble" noise is if one or more of the diodes are duff.

Never heard of this on a Bosch unit unless some idiot was welding on the van with battery connected.

Not easy to hear, but does it get worse if you turn the heater fan on (or as much load as you can put on the electrical system.)
Get your head under the bonnet, and get someone else to turn as much as possible on.

Other situation could be that the bolts are loose!?!??!
 

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Discussion Starter #3
May have to "eat my hat" here :eek:

Not easy to hear, but does it get worse if you turn the heater fan on (or as much load as you can put on the electrical system.)

Other situation could be that the bolts are loose!?!??!
Yeh. Finding it quite difficult to hear over the normal chutchutchut of the engine but it definitely seems to vibrate/rumble when the lights are switched on. The rumble seems to be there slightly when I initially start the van but then goes away. The rumble does not seem audible when the park lights are switched on - only with dims and headlamps on.
 

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Never had this problem myself (touch wood, won't have!).
Look at other threads about the pulley system.
I think there is one in the belt system that is known to "crumble" internally, causing a rumble noise.
Been a long day here, so can't remember which, but it's one of the main pulleys (crankshaft?) that has some sort of damper built into it.

I'd be surprised if it was the alternator, but you can try to find if the rumble comes from it with a long piece of wood pressed against it and your ear. (LONG piece of wood, so you don't get your ear in the belt:eek:)
 

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I'd definitely have the undertray off and eyeball the damper-pulley on the crankshaft just to rule it out. It's basically a dual-mass affair with a metal inner and metal outer joined by a wodge of rubber. When they fail it can be a bit spectacular.

Mine debonded and started slipping - you turn on the lights and it would just scream as the inner rotated faster than the outer due to the drag from the alternator. Pick up the revs and the noise stops - because alternators need less force to turn them as the speed increases, so the drag was reduced.

Also check belt tension, the tensioner pulley bearing, and the tensioner action itself.

It's not that any of these are more likely than a failed alternator - but got to be worth considering.
 

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Discussion Starter #6
Good advice @redpla. When you say "spectacular" do you mean it can take out/destroy other parts when it fails?
 

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Don't think you noted which engine?

It's been mentioned on here that the 2.5TDi cam-belt can be 'affected' by the damper or aux belt fragments getting into it. You'd need to be having a particularly unlucky day, though, wouldn't you?

Then again, if you take a gander at the damper pulley you'll see it's about 30mm deep and nearly the size of a dinner plate. The outer part of that coming free at 3000rpm and going for a smart stroll around your lower engine bay could be... exciting.
 

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Same engine as mine.

I wasted time and money on a replacement aux belt and faffing about trying to see what was "wrong" with the belt tension. When all the time it was the pulley. Diagnosed by main dealer in the end, at cam-belt change. Quoted me £180 + VAT (and no labour because it was off anyway), though when I came to pay they gave me a bit of discount.

BTW for testing you might be able to double the load on the belt just by pulling the light stalk when the dips are on. Doing that turns on main and dips together on most vehicles. Quieter than turning on the interior fan. If you've got A/C then that really loads up the belt, but you need interior fan on #1 to activate it of course.

Good luck tracking it down, whatever it is. Generally if something is slipping you get a screech - whereas you're getting vibration. Which sounds more like bad tensioner, breaking-up belt, failing bearing, or auxiliary component working loose - but doesn't even really match those. You've got an odd one. If the alternator regulator has gone potty that could lead to rapidly changing loads on the belt - though I've never heard of it specifically - just thinking aloud here. Even the energiser wire having a dodgy connection - rattling on and off - might cause the alternator load to keep fluctuating. Straws. Clutching. At.

The only similar thing I've encountered was a seized freewheel-type alternator pulley on a Scenic. At idle the belt went mad with vibration and the idle revs were all over the place. But a T4 has a damper-pulley on the crankshaft and no freewheel on the alternator (I think).
 

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Discussion Starter #10
I've just recently had the timing belt and clutch full job done. I haven't driven the van far since that job. I would have presumed something like this would have been spotted then? Or perhaps it is as a result of the timing belt job that this is now happening.
 

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When my T4 is idling and I turn on the lights there is a vibration sound which seems to be coming from deep within the engine.

I'm thinking the alternator is on its way out or something is loose in it causing it to rumble/vibrate when a load comes on it.

Anyone else have similar issues?
Could be as simple as your timing is slightly out causing poor idle ! May require a simple tweak !
 
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