Knock sound when hitting bumps at speed - Mustang Evolution

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Old 10-01-2016, 07:05 PM   #1
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Knock sound when hitting bumps at speed

So just within the last couple of days there has been an odd/terrible noise/feeling when i hit a dip in a road it sounds like something hits the under side of my car, not so much the ground.
This is confusing cause my car isnt lowered at all? im thinking maybe its the upper controll arm? i installed an adjustable one from BMR although i did that a while ago and didnt hear anything.
Also i installed adjustable lower control arms so im not sure whats going on.
it feels like im bottoming out or like the shocks/struts are stopping me from going down further once i hit the bumb.
The sound is coming from the rear center area of the car when the back end of my car hits the bump

in the video attached it made a different noise more like a scraping rattle ive never heard it do that before? usually its like a knocking thud just once, and only when the rear end hits the bump

---------- Post added at 01:05 AM ---------- Previous post was at 01:05 AM ----------

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Old 10-01-2016, 07:07 PM   #2
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Old 10-03-2016, 07:26 AM   #3
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Bad rear sway bar bushings?
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Old 10-03-2016, 07:38 AM   #4
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Did you make sure all the jam nuts are still tight on your adjustable LCAs? Had one loosen up on my adjustable PHB once.
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Old 10-03-2016, 08:06 AM   #5
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rear sway bar end link bushings?
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Old 10-03-2016, 09:07 AM   #6
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I'll have to check up on that and make sure it's all tight when I get the chance it's gotten worse recently hopefully it is just loose parts to tighten

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Old 10-03-2016, 10:15 AM   #7
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My adjustable upper control arm actually loosened up over time. (My fault for not tightening it right) and it did hit the underside and made a wacking noise any time I hit a bump or even if the road had a sharp divot in it. Like someone just smacked the underside my car with a pipe. When just looking at it parked, everything was tight and looked okay, but the actual angle was so far off from it extending out all the way that it caused the problem.

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Old 10-04-2016, 06:04 PM   #8
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Quote:
Originally Posted by ibejt View Post
My adjustable upper control arm actually loosened up over time. (My fault for not tightening it right) and it did hit the underside and made a wacking noise any time I hit a bump or even if the road had a sharp divot in it. Like someone just smacked the underside my car with a pipe. When just looking at it parked, everything was tight and looked okay, but the actual angle was so far off from it extending out all the way that it caused the problem.

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I was thinking that's where the knock sound came from I definitely need to check that.
So you tightened the bolt underneath the rear seats correct?

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Old 10-04-2016, 06:42 PM   #9
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For me it was the adjustment nuts on the actual control arm itself that came loose for me, making the "arm" or whatever far too long, which threw everything off and made the control arm smack any time the rear suspension had to do anything. Basically I didn't tighten down the one nut (on the arm itself) after setting it and driving/vibration loosened it up and it just slowly elongated itself.

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Old 10-05-2016, 09:18 AM   #10
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Quote:
Originally Posted by ibejt View Post
For me it was the adjustment nuts on the actual control arm itself that came loose for me, making the "arm" or whatever far too long, which threw everything off and made the control arm smack any time the rear suspension had to do anything. Basically I didn't tighten down the one nut (on the arm itself) after setting it and driving/vibration loosened it up and it just slowly elongated itself.

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Damn, I'll have to check that out, what did you use to measure the difference in angle from the drive shaft to differential? I used an app on my phone since neither I not the auto shop I used had any way to measure it

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Old 10-05-2016, 09:48 AM   #11
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I set it originally with my phone as well, but then I just had a shop set it and fix it when they did my 3.73 gears.

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Old 11-12-2016, 11:35 AM   #12
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So just as an update if anyone was wondering I fixed the issue finally so I called a shop about a read gear install (this will be the second set of gears not including original) they suggested I look at the upper control arm and tighten it with a crescent wrench.
I took a look and both nuts were so loose the tightened down on the center nut.
I'm assuming this is from not tightening them enough and the cars vibration. Also there were grind marks where my drive shaft joint sticks past the differential joint (one piece aluminum although the joint is steel)
I had the shop switch me from 4.10 to 3.55 gears, refill my differential fluid, and adjust my pinion angle. Total cost was $390 put in aliso viejo California from GRC performance they did a good job
Originally the did underestimate the control arm issue I guess they didn't think it would vibrate so much it elongated itself (it did) so tightening the nuts back down didn't help ( the drive up to their shop was brutal on my car just hearing it smack and grind)
I wanted to thank you guys for the help
Also the noise on the front end of my car has subsided for a time now, not sure why but it was once I got my car back?
I'll see if anything is wrong with my car again after I take it back out of storage in 6 months

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Old 11-19-2016, 06:14 AM   #13
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One of my end link bushings were bad and I heard a clunk every time I hit a bump. Changed out the end links and the problem is gone.
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