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2-stage drivetrain clunk under light load


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Cannot find solution to this problem on threads so here goes: 2006 Legacy sedan with auto transmission and 130K miles. In slow stop and go traffic I can feel and hear a metallic "clunk" upon light acceleration, and sometimes another one right after it on deceleration. Checked all joints, tranny mounts, misfiring, drive train--could not see anything but may have missed something. Thought it was the tranny mount but the two rubber blocks look and feel solid. No problem under hard acceleration/deceleration. Feels like something heavy is loose, and is shifting its weight in the opposite direction that the car is accelerating in. Thanks for ideas and best guesses, and ideally how to diagnose too if possible!
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I have an '09 2.5i automatic with the same exact issue. It is driving me bonkers. I have a lift in my garage and I have been over this car with a fine-toothed comb and I can NOT find the source of this noise. To make it even more annoying, about half the time when it occurs it sounds like it's coming from different directions. I'm baffled.

 

It almost sounds like a loaded structural member that has developed a crack and is deflecting under a load - making the sound. Sometimes I can actually 'feel' it in the floorpan of the car with my feet.

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Sounds like a U-joint going bad.

 

In these cars its most likely the carrier bearing.

 

Grab the driveshaft (propeller shaft) near the carrier bearing and see how much play is in the joint. There should not be much at all. If you can move it with little force, replace the propeller shaft.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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mechanic58: Good to know I am not alone....we can start a support group.

Someone: Please help us!

 

Great idea. I studied mine some more last night after I got home from work. The noise is definitely originating in the vicinity of the engine cradle crossmember and seems to be stimulated by movement of the chassis. I have examined my lower control arm bushings very closely, however I have not removed the lower control arms for the purpose of this inspection. There are no obvious problems. During the course of my inspections I did find a loose ball joint that I was SURE would fix the problem...there was no change after I replaced it. :confused:

 

Edit: I replaced this ball joint a couple weeks ago. This has been an ongoing problem with this car ever since I bought it.

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Thanks mechanic58: Will check sway bar link. Would be amazing if were the cause.

Maxcapacity: No play in joint but need to turn shaft more than seems normal before rear wheels turn.

Additional info on my end: Definitely feel a mechanical sound and vibration in tight radius turns in either direction.

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I had a similar issue when I first bought my car. There was a knocking sound around 2.5K RPM. It turned out my front sway bar bushings was worn out. It split down the middle in the bracket and I didn't noticed it until it completely split 6 months later. I replaced it and the noise when away. Something to look for.
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Looky what I found...

 

 

This is on my car, just now. Problem solved.

 

Yup. Mine broke completely after a few months at the ball joint. Ironically it stopped making noise then, lol. Fix video I used below. And yes, I had to use an angle grinder on one of the bolts like this guy did...

 

 

2 hours and $40 later no noise and notably better handling

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