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  • Squeal AC Belt

    My AC belt runs off the water pump pulley. About 2 months ago it started squealing with the AC off and only while goosing the throttle. It got to the point where it became more constant and is more affected when the AC is on. I replaced the belt because I saw it "bouncing" on the top run only more under load. The new belt is tight when the compressor isn't engaged, and "bouncing" when the AC is engaged. I straightened the compressor, adjusted the tension, and sprayed the belt with CRC belt conditioner. The squealing always returns. I'd suspect the compressor, but if it just doesn't seem to be coming from the unit. Maybe it doesn't like my belt?

  • #2
    Dean:
    If you spray the belt with dressing and the noise goes away, there is a high probability that the belt is causing the noise.
    The AC compressor clutch has a bearing in it, which allows the clutch assembly to spin free until you want to engage the compressor. This should only give you some kind of noise when the compressor is not engaged.
    The bearings inside the compressor only rotate when the compressor is engaged. If these bearings or anything else in the compressor is giving you problems, there should be no affect when the clutch is not engaged.
    You said the belt is noisy when not engaged and gets worse when engaged. If a new belt didn't solve the problems it could be the drive sheaves themselves. In time they can get highly polished and cause a belt to slip. Maybe you could try to clean the sheaves up with some light sanding and see if that helps. You could do that with out removing the belt by manually rotating the shafts and cleaning the exposed area.
    One last note. You did state that the AC belt is going from the water pump to the AC compressor. I had put a belt on my car from the crank pulley to the water pump and over the AC pulley. Belt made noise like crazy. Took me a while to realize the sheave sizes were incorrect and it would never work that way. Put on the right belt and all was good.
    Nyles

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    • #3
      I'll try anything. I did use brake clean on the pulleys before putting on the new belt. Funny the noise goes away at freeway speeds then returns-if the AC is on-at idle or low RPM. I'll try the sandpaper. It definitely will not squeal if I never engage the AC from the start of the drive.

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      • #4
        Dean:
        Does the belt only make noise when the AC is turned on? From your original post, it sounded like it would squeal, even when the AC was turned off.
        Nyles

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        • #5
          I have an important but simple question... Do you have TWO belts that span the damper and water pump pulleys?

          If you do, that setup is WRONG. The crankshaft ultimately drives all the belts. Typically, the damper will have one belt span the water pump and maybe the generator. Another belt may come off the water pump to the power steering pump. Another may originate at the damper and drive the A/C. All that is ok as long as you do not have two belts that span the damper and water pump pulleys because different sheave diameters are NEVER identical. We've seen setups where the belts melted from so much friction from fighting each other.

          Follow your shop manual pictures and keep sand paper away from your sheaves because the abrasion tears up the rubber. - Dave
          My latest project:
          CLICK HERE to see my custom hydraulic roller 390 FE build.

          "We've got to pause and ask ourselves: How much clean air do we need?"
          --Lee Iacocca

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          • #6
            It is normal for the AC drive belt to "bounce" to sum degree as the AC is operating; as the compressor is a reciprocating unit with varying loads applied to the drive belt(s) thru out each cycle, and as a certain elasticity is present in the assembly, particularly in the drive belt(s). Excessive "bounce" may be present with improper belt tension, mounting defection and perhaps excessively high compressor pump head pressure?

            If the pulley(s) have developed a smooth bright & shinny (glazed) texture upon the drive face surfaces, it may be necessary to "break" this sheen and acquire a somewhat more textured surface for best "belt grip". Light scuffing with good technique (important) and appropriate sandpaper will work. In this situation, I will remove said pulley(s) and glass bead or sand blast these surfaces for a more uniform surface texture. Obviously, we don't want to create a surface of an excessively abrasive nature and therefor imparting such abrasion to the belt(s), but is is necessary for the belt to "grip" the pulley in order to impart the drive force required in operation.

            "In the old days" a quick-fix was to sprinkle Bon-Ami on these surfaces (belts & pulleys) to scuff-up the surfaces, close the hood before starting, or then you get to wash the car! Scott.
            Last edited by pbf777; September 24th, 2016, 09:52 AM.

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            • #7
              The AC runs off the outer water pump pulley
              My cars do not have AC, so I am guessing at this. Shouldn't the AC belt also go around the crank pulley? If not, could the belt that is driving your water pump pulley be doing the squealing? Probably wrong, but I've always thought the load of an AC compressor required the belt to go around the crank, that's all.

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              • #8
                Yeah Joe, you're right. Let me amend my post:

                My set-up has the alternator running off the inner water pump pulley and the inner crank. The PS runs off the outer crank pulley. The AC runs off the outer water pump pulley. Everything lines up perfectly.

                The problem occurs when I turn on the AC, but the squeal continues after I turn off the AC until something changes, like a load change, and the squealing stops. Once the squealing stops and if I never turn the AC on again, there is no squealing. It is as if the AC clutch doesn't disengage immediately after turning the AC off.

                The AC load definitely, most definitely, contributes heavily to the squeal.
                Last edited by Deanj; September 24th, 2016, 03:41 PM.

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                • #9
                  Your setup sounds ok (after your revision). And the pulleys are large, with a lot of surface contact area. If your belts have proper tension, you should hear squeal out of either the smallest pulley (your alternator) or a failed bearing.

                  Watch your compressor as it turns on and off. you should see the clutch disengage the pump, then 'freewheel'. If the bearing is shot the pump will not disengage. Again, I think you can see this from the outside.

                  Typically, the alternator or generator belt squeals, usually in winter when the battery is half dead, it's dark and the windows are frosted. With all that draw, the alt can only charge the battery when the engine is at running speeds. So I suspect, if your bearings are ok, your alternator may be the culprit, evidenced by the fact that squeal continues after the mechanical load is removed from the A/C. At that point, the alt is still trying to recover lost battery power. - Dave

                  Factory finish on all pulleys is simply black paint.
                  My latest project:
                  CLICK HERE to see my custom hydraulic roller 390 FE build.

                  "We've got to pause and ask ourselves: How much clean air do we need?"
                  --Lee Iacocca

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                  • #10
                    This brings back Old Shade tree remedies LOL
                    I remember as a kid seeing people take a bar of soap and with the engine running hold it to the underside of the belt until the squealing stopped, Knew several old timers that just kept a bar of soap under the hood for when it started squealing again

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                    • #11
                      Been there and done that (often)! Still have a couple of pieces of soap in the tool boxes for that quick temporary fix.

                      Does that make me an "old timer"?

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                      • #12
                        Dave, you might be correct about load because things changed again last night.

                        I drove her about 6 miles while still light outside and no squeal. After parking and shutting down, I started her back up to move to different parking spot and the squealing began, much to my surprise. After sitting for 2-3 hours, I started her up again and she never stopped squealing until I shut her down in the garage. Of course the lights and heater were on which means there was a good draw.

                        I'm going to zone in the alternator because it I installed that a couple months ago and the problem started shortly and slowly after that. Also, there's no noise at freeway speeds when the charging is optimum. It makes sense and fits your scenario.

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                        • #13
                          While you are at it, check ALL the belts for cracks and just as important, if the sides (gripping surface) are shiny or not. IF shiny, replace them. I would do them all at this time since they don't cost a lot and you have the tools out and working right there.

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                          • #14
                            Originally posted by Deanj View Post
                            ...Also, there's no noise at freeway speeds when the charging is optimum. It makes sense and fits your scenario.
                            Depending on the battery's ability to store (I'm assuming it has no shorted cells), charging may be complete by the time you get to the freeway.

                            We buy alternators based on their charging rate AT IDLE SPEED, not because we need 70 or 100 amps. The more output, the harder it is to turn. What's worse is, some higher output alt's use the same pulley diameter as a 30-amp generator.

                            I understand that smaller pulleys make the alt run faster but small pulleys have very little belt surface area. To remedy, either use a larger diameter pulley because it's easier to turn (a longer lever) AND it has more belt surface area OR use a double-groove pulley.

                            Alternators don't 'spread out' the charge. They give all they can until the regulator tames down the charge (when the battery is full). Consequently, the most charge comes when your engine is starting up from idle speed, like at a light. This is the most likely time for belt squeal. - Dave
                            My latest project:
                            CLICK HERE to see my custom hydraulic roller 390 FE build.

                            "We've got to pause and ask ourselves: How much clean air do we need?"
                            --Lee Iacocca

                            Comment


                            • #15
                              Dave, I bought Larry's Thunderbird alternator conversion kit back on May 31st. It contained the brackets and a "65 amp" Delco 10si alternator. I assume it's a 10si from descriptions.

                              Assuming Larry's quotes their express warranty and will not honor the implied warranty that it wasn't fit for its purpose, would I purchase a 63 amp Delco 10si and transfer the pulley? And since you recommended a double grove pulley, could I transfer the old pulley from the generator? I have fused this at 100 amps.

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