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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 07-30-2014, 09:21 AM   #1
Mindspin311
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Clunk/knock from the rear, can I see subframe cracks/tears easily?

So, I starting hearing a knocking sound from the rear of the car yesterday evening. It was about 10pm, so tough to see things. I took the right rear off (where I heard the sound) and did a quick visual inspection.

Everything seems intact. Though I could not get a good look at the subframe. I used a rubber mallet and tapped on the trailing arm, control arms, swaybar and all sounded solid.

My first thoughts are RTAB (mechanic told me they would need replacing soon) or dreaded subframe. Can an RTAB quickly tear away?

Would I be able to see damage to the subframe area without actually removing any parts of the rear suspension?
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Old 07-30-2014, 09:23 AM   #2
Mindspin311
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Forgot to mention, at first I thought it was a loose wheel. As the sound was feint, then gradually grew. At one point it sounded rhythmic, sort of what a loose wheel would sound like. Checked all 4 corners and they were tight.

The sound doesnt happen only over a bump. Just slowly crawling through my neighborhood I was able to hear the noise.
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Old 07-30-2014, 12:54 PM   #3
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you can usually see the ones you can feel without dropping the subframe. small cracks can hide, large ones are able to see. big tears are obvious.
i don't think it's your rtab.
could be your rear shock mounts. or something driveline like half shaft cv joint, your guibo or center support bearing.
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Old 07-31-2014, 08:12 AM   #4
Mindspin311
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Took some pictures last night. Everything seems solid.

Guess Ill move on to checking nuts and bolts to make sure everything is tight.

https://www.dropbox.com/sh/fxpsfk37h...6fc3CNYOO7g4Ia
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Old 07-31-2014, 09:10 AM   #5
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Did you check your differential bushing? I don't see a picture of that. In the past that caused a clunk/knock for me.
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Old 08-04-2014, 11:08 AM   #6
Mindspin311
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I checked all the various nuts and bolts to make sure everything was tight. The worst I found were the upper shock mounts in the trunk. I got maybe a half turn out of the 2 12mm nuts.

I proceeded to recruit my wife to hang her head out the back window to look at the right rear wheel to see if there was any movement.

As we were driving down the road, she felt a knocking through the rear seat, specifically very close to the door itself. Coincidentally, that is exactly where the RTAB mounts.

So, what is the possibility that my RTAB has just complete torn? When I was under the car, I could pry the trailing arm from side to side, but it didnt seem any worse than the driver's side.

What could I use to try and shim the trailing arm in place temporarily to see if the noise goes away?
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Old 08-07-2014, 04:49 PM   #7
Alex323Ci
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sure it can be the rear trailing arm bushing. but knocking while driving and rythmic sounds again more like a driveline issue. something like the guibo causes vibrations through the floor and feels like it's at the rear very often.

could also be the driveshaft center support bearing and/or the driveshafts.

here is a nice write-up of how to check if it's your guibo
http://www.rogueengineering.com/bmw/GUIBO.html
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CF CSL LIP - NAVI - BMWPERF CF STRUT BAR - BMW GROUP N MNTS - GRUPPE M CF INTAKE - SUPERSPRINT - UUC BRKLINES, TRANS, RTABs - H&R SWAYS - 4.10 M-SPORT DIFF
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