Aux belt tensioner bolt snapping

[jgreenwell]

Hi all, my first post so here goes. I have an 03 plate Passat Tdi Sport estate, remapped to 160ish.

About 2 months ago she got a little noisy on tickover, rattling sound, and the tensioner unit shock bushes had failed, so replaced that, genuine VAG bit.

3 weeks ago, whilst pulling onto drive the tensioner bolt snapped, taking a chunk out of the pulley wheel with it. Anyway my father-in-law who works as a panel beater for main dealer repairer for VAG, BM's, Volvo's etc dismantled the front end, and we fitted genuine VAG components, pulley unit, and bolt, tightened to 25 lbs ft. Managed to get the bit out. Had sheared off just at the top of the threaded section.

All was fine, not sounding too bad, still a little clattery though. Anyway started her up this morning, ran fine on tickover for say 30 seconds, then engine note changed. Swicthed off, popped bonnet, sure enough, bolt had snapped again , no other damage though.

Stripped her down again tonight, sure enough gone in same place again. I love my Veedubs but this is starting to drive me nuts.

Has anyone got any ideas as to why this is happening, seams strange that she has gone 95K no probs, snapped bolt, then 3 weeks later another one gone.

Kind regards
Jonathan

[TheMadhatter]

I have heard of the free-wheel on the alternator malfunctioning and causing the bolt to fail and break belts. Could be worth checking out.

https://www.vwaudiforum.co.uk/forum/s...belt+tensioner
https://www.vwaudiforum.co.uk/forum/s...belt+tensioner

[jgreenwell]

I have heard of the free-wheel on the alternator malfunctioning and causing the bolt to fail and break belts. Could be worth checking out.

Cheers for that I will check it out. I have been reading elsewhere about that too, and I have been looking at a few forsale posts on pistonheads.com, a few mention "New alternator belt, tensioner, pulley and alternator pulley!", I will follow that route I think

Kind regards
Jonathan

[mcgoual]

Just Wanted to say thanks this thread was extremely helpfull, have an audi a4 1.9tdi 130bhp 2002, replaced aux belt tensioner & belt first.

Felt no binding in alternator pulley or power steering pump to suggest they were causing any problems, or indeed the fiscous fan was fine, went for 3 or 4 weeks, still vibrating a little but didnt think anything of it, then the bolt on tensioner snapped off , luckily the broken bit of bolt, almost an inch, was loose inside the threads and was able to turn by coaxing it out with a screwdriver mm by mm..

replaced bolt and 1 day later snapped again... read this thread, went back at it attempted to remove alternator which is trickier then it looks.. there are 2 connectors on the back of it, they come off ok, there are 2 bolts holding it on, the top one is fine, the bottom one will not come out fully as the hub of the fiscous fan stops you from removing the bottom bolt all the way.. so you must get a 6 or 8mm allen around the back of the fan, under the alternator and loosen the bolt that secures the fan which comes forward then, so you can get the bolt out and hence the alternator..

Brought the alternator to auto-electrician place that specializes in alternators and they changed the pulley and checked it was charging etc cost €50, fitted and tensioner no longer vibrates, all sounds alot better fingers crossed, so thanks again

[Gary03]

I reckon this is indeed a failing alternator causing these bolts to fail but my story is slightly differant.
My aux belt tensioner would 'chatter' and it done this for months, i didnt really know when it started but i could hear the belt and tensioner whilst it was ticking over stationary.
Then, the alternator stopped charging one day and needed replacement. Fitted new alternator and now the tensioner no longer vibrates. It was the alternator that was deteriorating over a few months before it packed in causing this vibration on the tensioner.