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Belt squeal mystery?


cb350

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Hi all,

 

I've searched high and low about this but can't find anything definitive...

 

Late last year (December) I replaced the two belts on my '03 350Z with the Gates aftermarket belts. The old ones weren't making any noise but were very highly cracked.

 

Then at the end of January, the belts started squealing/screeching like crazy at start-up. Or at least, I thought the belts were making the noise - it sounds exactly as you would expect belt squeal to sound.

 

So anyway, checked the tension of the belts again (assuming they have stretched a bit) - didn't seem to be any problem there.

 

Thought maybe the old battery was dragging things down and maybe this was the source of the problem - changed that - no difference.

 

Tightened the belts up a bit and this seemed to improve things for about 2-3 weeks, then the noise returned. I guess this was around March/April by this point.

 

So, I took both belts off and tried all the pulleys to check for any play, resistance to movement or noise. Everything seems totally fine. Put it all back together, tension correctly, noise disappeared for a little while but soon came back again.

 

I found if I select a high gear, bring the clutch up to try to stall it, let the engine revs drop sufficiently and then push the clutch back down, the belt noise goes away.. so I just started doing that in the mornings! (not ideal but I haven't burnt the clutch out yet ;) )

 

Anyway, a couple of weeks ago I got really fed up of it, got back under the car and had another look. Belts still seemed in good condition but the AC belt looked a bit loose so I decided to tighten it up a further just to see what would happen. I didn't go nuts but I took a bit of slack out. If anything, it may actually be worse now.

 

Having the AC switched on definitely makes it worse. Once the engine has warmed up, I can't get the noise to happen. Even starting it again an hour or two later, it won't squeal.

 

I'm slightly stumped. I was thinking my next move would be to have a good look at the idler pulleys on the AC belt tensioner - probably remove it to get a close look?

 

But what I don't understand is that it sounds exactly like belt squeal. Could the AC pump make a similar noise?

 

Sorry for the long post, but does anyone have any idea? What would be the next best thing to look at? I bought another brand new set of belts but after inspecting the ones on the car, it just didn't seem worth replacing them again... although I probably will replace them anyway next time I pull the undertray off.

 

By the way, it's really loud. You can hear it all the way down my road when I'm inside my house. At least I'll know if somebody is trying to nick it I suppose!

 

Chris.

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Thanks Alex.

 

Do you think it's possible that the same sound could be heard if it was under-tensioned or over-tensioned? I'm just wondering if I've over tightened that AC belt now.

 

Haven't tried taking each belt off in turn... the main problem is I don't have much space where I live, so I drive it to my dad's house (he has a pit in his garage).. and then of course it's warm and won't squeal. Even leaving it a couple of hours, I've never heard it while I'm there!

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  • 2 weeks later...

So, just an update on this...

 

The noise only happens at start-up, and although it can be heard with or without the A/C switched on, having the A/C on makes it more likely to happen (and switching the A/C off is a good way to stop it).

 

I already checked all pulleys, etc, but I decided to pull the A/C belt off again and dismantle the tensioner. Nothing wrong there, so far as I can see.

 

Put it all back together, retensioned the belt again, and the squeal is now worse than ever before!

 

I'm now thinking it has to be the A/C compressor. The pulley feels absolutely fine and turns without any play, but I've pretty much ruled everything else out. To test, I ran the car with the squeal happening, got underneath and fired WD40 directly into the centre of the compressor pulley (being VERY careful not to get any on the belt - not easy when you're being deafened). Conclusion: 1. Buy earplugs. 2. Squeal stopped immediately. Later when I restarted the car, the squeal was back.

 

Does anybody know if it's possible to dismantle the pulley/clutch assembly on the compressor with it in-situ on the car? I'd really like to take a look behind that pulley without having disconnect the entire A/C circuit.

 

Cheers,

 

Chris.

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  • 7 months later...

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