You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Yes, that car again.
There's a booming vibratey rattle at idle, and it's the auxiliary belt making it. It can clearly be seen vibrating, and if I put the (smooth) head of a ratchet on the section of belt that's vibrating the worst, it stops.
So my question is this: is this definitely the tensioner pulley, or could it be an old/bad belt? When I move the tensioner manually (with molgrips on it) it feels sort of sticky - not moving smoothly. I can see how this could cause it not to return quickly enough. But the issue is I changed it maybe 12-18 months ago. So it shouldn't be that. Could an old/stretched belt be the issue instead?
Pistonheads ------>
If you've worn out a tensioner pulley (and possibly belt) in 12 months I'd be checking all the loads on the belt to make sure they move freely. Anything getting hot?
Could be. Would you not change in a set anyway? Belt tensioners can often feel sticky/weird when manually moved, it's not that good a test compared to the normal movement so you can't read too much into that but obviously something's off. In these timescales it'd probably have to be some other issue taking the belt out with it it seems, like, a fitting issue or a bad aux component?
Is it definitely the belt itself making the noise? What I mean is, it's obviously the source but is it the "noise" or is it making vibrations that make something else vibrate that could be handled easily?
Also, is this an aux belt with consequences, or is it the sort that if it breaks you just gradually run out of volts and eventually break down painlessly? My mondeo took its original one to the grave, at least 50% past the deadline and with loads of cracks, I figured if it broke I'd fix it.
It's the belt that runs the alternator and aircon.
It's possible it's the alternator clutch pulley I suppose. Actually.. reading about it that might be it.
I would say alternator or even water pump bearings going.
Water pump is on the timing belt.
If it's the pissat
Then first port of call for any abnormalities in the aux belt area is alternator clutch.
It's a free and easy check.
Easy replacement too.
A friends Volvo V60 had a failed auxiliary belt and it borked the engine.
HTH
What car is it on?
I had similar with my old T5, it felt like the tensioner was a bit rough so I changed it with no improvement. The alternator sounded ok when it was in situ but when I removed it and checked it was obviosuly the bearing in the alternator which had failed. Once I replaced that it was good as gold.
What car is it on?
Passat TDI 2006.
Just about to order a new one and the tool. Thanks for the reassurance folks. I don't think I want to drive it in this state, which means the MOT re-test will have to wait.
Sounds like alternator clutch seized.
The clutch only really works at idle to take the resonance out the belt, so just rev it enough to get past the resonance. The worst it'll likely do is wear the tensioner pivot out and cause it to throw/shred the belt, but they usually take a good length of time seized before that happens.
On the Ford TDCi this rattle in the aux belt can be caused by the crankshaft pulley...it's got some sort of bush/damper that wears, or something that causes it to vibrate, and 'excite' the belt.
Mine used to do it at idle when at operating temperature, just the slightest increase in revs (even just turning on the air con) would shut it up.
they usually take a good length of time seized before that happens
It only started last Tuesday when I took it for its MOT in Newport - so it drove 15 or so miles. If I drive it back to get its re-test in the same condition another 15 miles do we reckon it'll be ok?
Oh apparently you can increase the idle speed on some VAGs, I'll give that a try temporarily.
It usually takes several thousand miles before anything will fail, unless something was on the verge of failing anyway.
Moly, you should disassemble/reassemble the entire interior - just to be sure as you never know... 🤔
Have had them go on slightly older passats and they normally also give a judder to the power steering towards full lock when stationary. I ran our for several thousand miles before changing it with no issue. Can't imagine it would failstraight away or constitute an MOT failure. Its easy to check if you can remove the tension from the belt, soin the pulley one way and it should free wheel and spin it the the other and it should be solid once they fail they are solid in both directions.
check the belt with the aircon on then off. my daughters aux belt makes more noise when the aircon clutch is engaged.
Assuming the alternator clutch is the problem, if you've 100k + miles on the clock, don't just replace the alternator clutch, fit a new alternator and then only a top quality one - OE, Delco, Bosch etc.
Noted, Marko thanks.
And thanks for the reassurance everyone else.
Moly, you should disassemble/reassemble the entire interior – just to be sure as you never know…
Actually.. funny you should say that. The interior temperature sensor seems to have gone a bit nuts, so I think I am going to have to do that again anyway!
Handy tip for locating noisy pulleys
I took to Newport to get the MOT re-test, only to be told I'd changed the drop link on the wrong bloody side.
took to Newport to get the MOT re-test, only to be told I’d changed the drop link on the wrong bloody side.
Shoulda parked facing the other way....
Also get on the pistons heads thread arguing about near and off side vs left and right and passenger and driver.