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Date: Thu, 29 Jun 2006 13:44:42 -0400
From: Charles Molhoek <molhoeknospaml.com>
Subject: 9000 Drivetrain noise . . . help!


Ok, please tell me someone knows what is going on here! I have a '97 9000 Aero with 200k miles. Recently (about 300 miles ago) developed a weird metallic knock in the left front drive train (it actually sounds like the 'click' from a torque wrench, just 20 times louder). It occurs when I accelerate and also when I let off the accelerator. The more gently I accelerate, or decelerate, the softer the noise. If I disengage the clutch before decel, I don't hear it. The noise sounds like a light clunk in the cabin with the windows up, but with the left window down, it's up to full volume. You can not hear much from the right window, so it's definitely on the left side. The weird, and disturbing, point is that it came on very suddenly, I did not notice it building at all. Listed (far) below are the steps I have taken to isolate the problem (so you can skip over as much of my OCD babble as possible). Being the cynic I am, I have now assumed that the problem has maximum PITA potential. There seems to be an abnormal amount of play (in terms of how many degrees you can rotate the wheel) in the transmission when rotating the left wheel back and forth (tranny in gear, right wheel on the ground). In addition, it sounds a little loud the differential housing when I rotate the wheel. It's much less noticeable if the tranny is in neutral and you can freely spin the left wheel, but it is still there. My thought is there is some slop in the gearing in the final end of the trans, and the application of power, and also the compression braking of the engine during decel, are making two gears slap together over some excessive play, but I have no idea where! If anybody has any experience with this problem, or even any advice on what to do next (other than going to a mechanic, transmission shop, or the local theivin' Saab dealer), I would greatly appreciate it. Thanks, Charlie What I have determined thus far: The caliper is firmly in place and the pads show no problems (~60% thickness). The rotor retaining screw and wheel locating stud are snug and there is no play in the rotor/spindle mounting. The ball joint is tight and shows no signs of problems. The steering rack and links are tight and visibly fine. The inboard universal joint on the left side appears to be OK. The rollers and their needles seem to be fine and the drive cup shows no abnormal wear spots. The outer CV new, but I checked it anyway. There appears to be no slack and it moves smoothly. It is a OEM replacement (Lobro, not ScanTech) that has about 2 years and 30k miles on it, so it should be fine. The wheel bearing was shot, but it was replaced before this came up, so that should not be an issue. Just to be paranoid (a frequent problem of mine, you may notice), I swapped out the new bearing for an old one I had. The knock was still there, it was just harder to hear over the noise of a bad bearing. After returning the new bearing to it's proper place (with a new axle nut), the noise remained the same. The struts are new and their bearing pads seem fine. All mounting bolts are snug. Upper motor mounts, lower tranny mount and front lower hydraulic motor mounts are all new and snug, no issues there. The rear hydraulic mount appears to be fine as well. Exhaust does not seem to be knocking on anything.

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