AC belt coming off tensioner/roller

[CaseyJay]

I had a frayed AC belt on my '02 A6 tdi (AKE) and found no logical reason for failure except some serious grooves cut into the lower belt cover which made me think continued use and rubbing just wore it down in the end. Replaced belt and decided not to refit the cover as in current (poor) condition, looks like it would just contact the belt again. Tested it first and belt did move 1-2mm over the edge of the tensioner then reset itself when stopped. Checked torque as best I can in service position (I need front end completely off to get proper torque angle access).

Drove 350km this am nice and chilly. On the return leg, no A/C at all, quickly found belt had come off the tensioner, but seemed intact (will investigate further).

The other Aux belt also sits a little 'offset' on one of the rollers (it too frayed and cut into the cover a while ago). Is this normal? Is someting missing from the rollers/tensioner, like a cap that keeps the belt in line? I can't believe the purpose of the cover is to keep the belts on (see pic), so is something else wrong? thx2014-09-10 22.49.29.jpg

[zollaf]

a bearing or the tensioner has failed and is running at a silly angle, not quite straight, allowing the belt to run off.

[CaseyJay]

ok thanks, so if the tensioner 'seems' ok, I guess it could be the crank or the AC pulley which is gone bad, will pull the front and check both...

[zollaf]

with the belt on and under tension, use your eye or use a straight edge to see which one is running not true to the others.

[ceilidhalfie]

With regard to tensioner or pulley bearings going bad, with the belt off they should spin freely (by hand) and make little noise. If it is the aircon pulley, and you have a clutch type mechanism for engaging the aircon, then the clutch and then the aircon pulley can be removed. A local machine shop will press out the old bearing and press in the new for you. Check one of my posts on the subject to identify the supplier and replacement bearing number. When I came to do the cambelt changes on my 2002 Audi Allroad 2.5 AKE I found a sheared aircon belt, tensioner disintegrating and aircon pulley sound rough. All changed 22k ago and no problems.

[bagpipingandy]

For the large belt which does power steering, alternator, fan and a few rollers, it will be the tentioner pivot bearing bushes which are worn so the tentioner sits an an angle pulling the belt off the upper roller, you can tell if you hold the tentioner using the latge hex to retract it and if you can wobble it side to side,

the small aircon belt must be the tentioner bearing also causing it to rub off,

also note the belt cover must be fitted with 3 top hat spacers otherwise it will rub against the belts,

i recomend to check and change the bushes for the large belt, tentioner pivot, they are not expensive but a front off job, it is not the actual roller bearing but the pivit point of the tentioner which wears, their are small very thin bushed sleeves you can replace as long as it has not worn through the casting, mine were bad at 90,000mls with the belt rubing through the cover,

regards

Andy

[CaseyJay]

it will be the tentioner pivot bearing bushes which are worn

yes this caused my main Aux belt failure and replaced the bushes last year. It looks like all pulleys/rollers were last replaced about 65k ago, so I think I'll just have to check and replace the lot when I do my toothed belt next (due now anyway).

Cover spacers were in place so guess some wear in bearings over time has led to slippage.