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Old 08-08-2016, 09:42 AM   #15
OldNuc
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Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 64,752
 

1998 SC2
Default Re: subtle "rod knock" like sound, but the pattern is wrong

Quote:
Originally Posted by cityhawk View Post
I'm kind of thinking along these lines. I have a long drive to my second job in the morning. I'll double check the lug nuts before I leave... I did just do my front brakes. Otherwise I was thinking axle as a possibility. Perhaps I can put the front up on jack stands and get the car up to speed and see if I can reproduce it.

The sound is most pronounced while coasting in gear or under constant throttle or light load conditions. Pretty much goes away under acceleration.

I'd be very surprised if it were an internal engine condition... 163k, well-maintained engine (I've had it since around 67k miles, faithful oil changes and never running it low, full synthetics for the last 30k or so miles with minimal oil use (some leakage around the valve cover). Just to come out of the blue with a rod or piston problem would be surprising.... and the sound pattern just seems wrong.... it seems to be related to the drive train somehow, though only present when the engine is running with the drive train.
The caliper could be the issue and is easy to test. Induce the conditions that result in the noise and while holding throttle constant very gently press on the brake, if noise quits it is a sticky spot on a rotor. Declutching changes the thrust direction on the drive system, makes noise quit.

It is not excessive crank end play either.

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