BrandenZ Posted July 17, 2013 Share Posted July 17, 2013 Okay so: 240z R180 WRX STi 3.9 clutch type differential with johnc side axles mated to stock halfshafts Wheel bearings replaced roughly 2k track miles ago Ujoints also replaced with wheel bearings I'm seeing a very interesting issue that I can't yet pin-point that is only reproducible under extreme circumstances / race conditions. It seems to be correlated to heat, but I can't prove this per se. It seems like after say 25 miles of hard track driving, or 15-20 autox hotlaps, the car will develop a very odd clicking noise out of the rear. It's timed exactly with the rotation of the wheels. It happens in neutral or in gear. The longer and harder I run the car, the louder and more pronounced the clicks get, but they always have the same frequency. I have yet to be able to track it down, because the second the car cools down, even as fast as it takes me to get it up on a hydraulic jack and stands, the clicks disappear. The exhaust also runs directly underneath the diff (PO did it, don't look at me!). My fear is that the exhaust temps climb, cook the diff, thin out the fluid, and I'm slowly destroying it. My alternative guess is wheel bearings, as I've never heard of u-joints clicking. I'm thinking of just swapping the darn wheel bearings in an effort to throw parts at the problem and see if it magically disappears, but thought I'd consult the oracle(s) here first. Any and all ideas welcome! Quote Link to comment Share on other sites More sharing options...
johnc Posted July 17, 2013 Share Posted July 17, 2013 I have yet to be able to track it down, Track it down before throwing parts. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted July 17, 2013 Share Posted July 17, 2013 Do you have a disc brake conversion installed? If so, perhaps the edge of the rotor is too close to the caliper and when hot is touching the caliper (and not perfectly round). Look for wear on the edge of the rotor and inside of the caliper to verify Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted July 18, 2013 Author Share Posted July 18, 2013 That's a terrific suggestion! I will definitely check that out. Johnc / all -- any suggestions for how I might be able to track it down with any reasonable degree of success? It is absolutely not reproducible on the street, at least not in any legal capacity or one I'm willing to take part in. If it was, I could get it up on a lift in a hurry. About the only thing I can come up with is to beat her up on a track again, and have a buddy waiting with a hydraulic jack, pull off course as quickly as possible and get the rear up as quickly as possible with a mechanics stethoscope on the ready. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 18, 2013 Share Posted July 18, 2013 Look for new wear spots on the e-brake cables, brake lines, anywhere on the halfshafts/CVs, etc. Its most likely an external rubbing not an inside the diff thing. You should also change your diff fluid every couple events if its getting really hot. Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted July 18, 2013 Author Share Posted July 18, 2013 Thanks John, Pete. I'll check it all out and report back my findings. Quote Link to comment Share on other sites More sharing options...
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