'Belt chatter' like noise from a 2.3T 940

[gregharvey]

Hi all,

I've been reading a few threads on the forum around this topic, I guess I'm after some practical advice on how to diagnose the problem I'm having - what to listen for/check and where. I have a late ('97) Volvo 940 estate I've had for nearly 4 years now. When I first got it, it was pretty quiet. Then one day the alternator belt broke. I wasn't around, but a friend did something to re-purpose the air conditioning belt to drive the alternator so my wife could get to a garage (completely unnecessary, as the garage is only 5 minutes away - downhill - and the car was running, but he meant well and I wasn't there to stop him).

Mechanic put the aircon belt back where it belonged and replaced the alternator belt, but since then the car has made a noise a bit like belt chatter. At first it was intermittent, and we put it down to the replacement alternator belt, which was not a proper Volvo spare. It irritated me too much, and anyway, the 'wrong' alternator belt broke again after about 6 months, so I bought a set of Volvo belts and had the mechanic replace them all.

No dice, the chatter continued, initially intermittent but these days it seems almost constant and sometimes it seems to be a continuous noise instead of a 'chatter'. Mechanic said he doubted it was anything serious and 'it just does that', but it's always bugged me because it never used to - I'm now resolved to sort it once and for all, especially since I think something is getting worse and I don't want an expensive problem to arise from something that would've been easily fixed if caught in time!

So, what on earth is causing this and how can I diagnose? It had a new water pump about 3 years ago, timing belt was changed quite recently, I've read possibly oil pump, alternator, the belts themselves (don't think it's that), other suggestions? And how can I check each one?

Thanks in advance!

[david philips]

hi my advice would be to remove the belts (not the timing belt) run the engine to make sure the noise is not from the timing belt or tensioner etc if not then turn the alternator etc by hand and find where the noise is coming from, you could run the engine after each belt is removed to check if the noise goes.

could be a bearing failing in the alternator or water pump some non volvo water pumps do not last a long time, good luck .

[cumbrianmale]

Check your alternator mounting bushes. If they are worn when you tension the belt it will twist the alternator putting the pulley out of alignment.

[Sideways940Estate]

when i finished swapping my engine i had a really weird whirring noise when revved and when on rundown, turns out my alternator belt was on the wrong groove on the pulley and it was rubbing on the other belt!! il get a pic if u want to show the right pulled but i swapped grooves and it went away may explain why ur belt broke so quick too...

[MTerry]

You can also check the main belt sprocket coming off the front of the crankshaft. It has a hard rubber isolator between the metal hub and the belt grooves. It can separate and cause the belts to spin slower than the crank, and since it's rubber, it squeals just like loose belts. Eventually, all the belts will stop turning. Since an improper belt was fitted by your friend, maybe it was overstressed and separated. Listen for the squeal right at the crank, and see if there is a lag in the belt speed when the engine is revved.

[gregharvey]

Had a poke about with my dad, who is older and wiser and has spent a lot more time under cars than I have, and having listened here and there, it's definitely *not* belts or alternator. Doesn't sound like water pump either, nor is it oil pump - it's very loud at the front of the engine. Current theory is cam belt idler... As far as I can tell from the receipt when he changed the belt, the idler wasn't replaced... and the car's done well over 200,000 miles.

[gregharvey]

So having figured it wasn't the belts (though without taking them off) took it to the garage so the mechanic could have a quick look and he was adamant it was the belts and proved it. He dribbled a bit of what looked like de-icer on the offending pulley and the chatter stopped for a minute. So it is belts. He insists there's nothing you can do about it, but what's driving me crazy is we owned the car for 2 years prior to the alternator incident described in #1 and it *never* did this.

Why do we have terrible belt-chatter issues now, when we never did before? Is the mechanic right it's impossible to fix? Is it worth going to a proper Volvo dealer to get the alignment of everything checked?

*sigh*

[Steve940estate]

Mine started making a noise again. Gave it a squirt with WD40 just to see which belt it was and the alternator one was the culprit.

I took the belt off which has done a few years and it was showing signs of cracking. While it was off I cleaned the v grooves on the pulleys. They were a bit rusty and the surfaces where the belt runs were a bit shiny but not bare steel. Much rubbing with coarse Scotchbrite later and then a quick clean off with de-greaser and all is well again.

As you have a new belt try cleaning the pulleys up a bit and degrease it all before putting the belt back on.

[Husqyman]

Originally Posted by gregharvey

So having figured it wasn't the belts (though without taking them off) took it to the garage so the mechanic could have a quick look and he was adamant it was the belts and proved it. He dribbled a bit of what looked like de-icer on the offending pulley and the chatter stopped for a minute. So it is belts. He insists there's nothing you can do about it, but what's driving me crazy is we owned the car for 2 years prior to the alternator incident described in #1 and it *never* did this.

Why do we have terrible belt-chatter issues now, when we never did before? Is the mechanic right it's impossible to fix? Is it worth going to a proper Volvo dealer to get the alignment of everything checked?

*sigh*

Are you sure it is the right belt? I have read somewhere on here or possibly somewhere else advertising a belt that these are the correct width (do not remember the size, only owned a 940 for couple of months) if you have one thats two narrow it will bottom out in the "V" of the pulley causing chatter and/or squealing despite looking perfectly adjusted, could also be a worn damaged pulley?