97 ls400 190k. Car makes awful grinding 30% of time. Gets worse while accelerating peaks around 2000 rpm. First thought was mounts. No luck. It's been hard to diagnose because it comes and goes. Did a littler investigation today it started making the noise so I took the serpentine off and it ran quiet as ever. Power steering pump seems to work fine a/c blows cold noise present both on and off. It doesn't sound like it's anywhere near the alternator. I'm suspicious of either the fan idler bracket or the harmonic balancer. Any thoughts?
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Fan bracket, idler, tensioner or a/c compressor. Check and see if the noise comes and goes with the kick on/off of the A/C clutch. If it happens when the A/C clutch locks on it is a sign usually of the compressor going.
If it starts when the clutch kicks off and the Lully starts to free wheel, the clutch bearings are going. Usually spinning the compressor with the belt off will also make any roughness in the clutch bearings obvious.
Switching compressor on and off makes no change in noise. I recently had TB/WP replaced. I don't think it could be that because it quit with removal of serpentine. Tensioner felt tight and smooth but it's cheap enough to change anyhow. I'm really swaying toward fan idler. Can that bearing be replaced of is it one peice
I actually just ordered a fan bracket since the car is noisy while idling. Mad with myself for not doing it during my recent TB job. When I remove my serpentine belt it all smooths out though. All the pulleys spin freely except the power steering which gives slight resistance but does spin. With the belt on it is quite noisy and even shakes the engine enough to feel it in the drivers seat.