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Discussion Starter #1
I’m trying to find the source of a weird grind/rattle noise I hear whenever the ac is on in my 68 Coupe with a 302, T-5, and old air ac. Here’s the thing, it only does it when I’m at a dead stop at a light and I engage the clutch in first to get rolling. Once I’m on my way, all is good. I feel like the noise is rpm related, meaning that the initial slow move from a stop to go where the Rpms aren’t too high maybe don’t turn the compressor fast enough? Or the belt is slipping? Anyone experience something like this?
 

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Discussion Starter #2
Quick edit, meant to say the noise occurs when I dis-engage the clutch in first to get rolling from a light or stop.
 

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Quick edit, meant to say the noise occurs when I dis-engage the clutch in first to get rolling from a light or stop.
No, you were right the first time. When you let the pedal out to start rolling you are ENGAGING the clutch. I'd start by examining the driver's side engine mount and looking for something that is rattling against something else. Another potential cause is "belt slap" along the longest section of your A/C belt.
 

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Discussion Starter #4
I should’ve mentioned this as well, but this only happens when the AC is on. When it’s not the car drives fine and there is no noise from a dead stop to go. It sounds like it could be the belt, maybe a shorter one is in order and needs to be tighter.
 

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Like Woodchuck suggested, it could be "belt slap". I had the problem with my original factory compressor and cured it with the factory retrofit pulley. The vibration and noise was virtually eliminated.
736430
 

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I have a March Performance serpentine belt pulley that would freeze up during start-ups and then loosen up. Replacing the pulley took care if the loud noise and the belt slippage. Replaced the belt as a precaution. Spraying WD-40 into the pulley bearing verified the issue.
 
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