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Author Topic: Resonance from rear of car  (Read 2249 times)
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Pmustang
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« Reply #15 on: July 09, 2017, 12:43:18 PM »

Wife was with me today driving spiritedly and it was doing it quite a bit. Said she definitely thought it was coming from rear as I do. I need to get the car on a lift and check for loose items

It's so strange how it's almost always "Grnt, Grnt" two noises in quick succession. You would think it would vary in length  or continue longer.



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Pmustang
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« Reply #16 on: August 06, 2017, 09:59:25 AM »

No real update.

Had a friend with me today and by pressing down on tye rear corner of the car we could hear a bushing type squeak but that does not appear to be the noise

It's happening quite slot but it's nearly impossible to make it happen when you want it to.

I cannot make it happen on demand but low speed slight uphill roads seem to cause it more times than others 

Higher speeds may do it but with 65 side exhausts it's hard to hear the noise

I need to put the car on a lift to see if something can be seen

Cheers  Peter

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NC TRACKRAT
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« Reply #17 on: August 06, 2017, 11:21:44 AM »

I know this may sound rather simplistic but have you checked your emergency brake cable for any interference with the exhaust when released and not under tension?

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« Reply #18 on: August 06, 2017, 05:21:44 PM »

I've been monitoring this thread since the beginning and have been patiently waiting for someone to ask "how (or if) the side pipes were hung from the chassis". Since no one has asked and you (Pmustang) have not mentioned this topic, I will "officially" ask "how"?

I presume that the mufflers are suspended with rubber like all Hipo's. Is that a correct assumption? Next, are the side pipes somehow attached to the chassis? Are they isolated by suspended rubber hangers or they attached via "muffler shop" urethane isolators with a through bolt going to something solid on the chassis. My experience with this type of isolator is that they provide little isolation if they are attached correctly and NO isolation it they are crushed by the through bolt. The through bolt is the means of transmitting the vibration. If your situation is the latter, I think that you are experiencing the transmission of the natural frequency of the exhaust system somewhere into the chassis which is the resonance that you are experiencing. Also, the louder the exhaust system is, the more amplification you receive.

What is your situation? It is certainly something worth looking into.

Frank 

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Pmustang
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« Reply #19 on: August 07, 2017, 03:13:25 PM »

Guys. I promise to get the car on a lift and check these things

I work on these cars all day at work so working on my own gets the short shift

This will be a great one to figure out.

I have a repeating noise as well but thinking that's tyre related.  Need to chuck on some torque thrusts for a spell.

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1175
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« Reply #20 on: August 07, 2017, 03:52:29 PM »

Sounds like a ring and pinion issue to me.  New gears?  Aftermarket or original Ford gears?  Brand of gears can make a difference.  Was posi gear additive used after rebuild of rear end?

Jon

« Last Edit: August 07, 2017, 03:54:44 PM by 1175 » Logged
stickshift
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« Reply #21 on: August 07, 2017, 06:06:11 PM »

Sounds like a ring and pinion issue to me.  New gears?  Aftermarket or original Ford gears?  Brand of gears can make a difference.  Was posi gear additive used after rebuild of rear end?

Jon

Wow! I never considered that the "sound" might in fact be the normal sound of a "performance" ratio? I'm speechless. Huh?  Shocked

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Pmustang
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« Reply #22 on: August 07, 2017, 10:15:26 PM »

Car was stock with a 389 gear, made the noise and more before having the work done. Now a new 389 gear and the car still makes the noise.  I am sure it is not the diff. It was also rebuilt by an extremely well recommended thought of shop  here in the U.K. The noise is not related or in tandem with a specific speed or action as far as I can tell.

Thanks to the folks making constructive comments.

« Last Edit: August 07, 2017, 10:16:57 PM by Pmustang » Logged
Steve McDonald (formally mcdonas)
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« Reply #23 on: August 08, 2017, 02:32:11 AM »

Had weird noise in the rear of the car while driving and traced it to the right rear exhaust hanger, themtwo,bolts through the frame rail were slightly loose and it allowed the exhaust resonance to transmit through the car.
Was difficult to duplicate and was found by accident when I was cleaning under the car and notified the bracket moved when pushed against. A couple of turns with a wrench on the trough bolts and the noise went away

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6S1431 owned since 1971, driven cross country 3 times, daily driver until for almost 20 years, has over 200,000 miles on it. Every time I drive it it makes me feel like I'm 21 again
Pmustang
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« Reply #24 on: August 09, 2017, 12:08:50 AM »

Thanks Steve

My car has 65 Shelby side exhausts.

I will check the mounts for sure

Cheers  Peter

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67350#1242
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« Reply #25 on: August 09, 2017, 04:49:05 AM »

I've seen mufflers with loose internals causing random resonance noise like you describe. Have you tried banging around on the exhaust and listening for a rattle?

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Pmustang
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« Reply #26 on: August 13, 2017, 10:22:18 AM »

Okay, finally grabbed a video on a drive today

https://youtu.be/qAIUMWWk-GA

You may struggle to hear but it's happening a ton

I hear it in seconds 1-2, 5-6, 18-19, 22-23, 38-39 and 52

Let me know your thoughts

I've not had it on a car lift yet and it sits too low to get under.  But here is the sound nonetheless

Cheers  Peter


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OldGuy
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« Reply #27 on: August 13, 2017, 11:17:43 AM »

I think that you are at a point where you are going to have to start implementing some of the great suggestions that have been offered up by others. Unfortunately these gremlins usually don't go away by themselves and you can only diagnose things so far without going through the process of elimination of the things that it "could" be.

Let us know what you determine as you progress down this path. We can't help you much more until you actually try something.

Frank

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Pmustang
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« Reply #28 on: August 13, 2017, 11:43:51 AM »

1000 percent correct

I am sorry it probably seems daft I keep mentioning the issue and then not getting off my.
 Keister and looking myself

I work on Mustangs all day at work and that's where the car lifts are.  I leave very early for work so taking the Shelby wouldn't make the neighbours happy and we have so many cars to finish I haven't worked on my own stuff for ages

This week I need to bring it in though so will update

Sorry for seemingly acting helpless

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2112
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« Reply #29 on: August 13, 2017, 01:38:18 PM »

Not to be discouraging but I thought I would share this experience.

I ordered a '92 Bronco with all the extras. I loved the truck, but there was the most Annoying buzz/rattle between the speeds of 55 and 70mph. I had the dealer try to resolve it but stopped that when they just wanted to start caulking everything.

The noise drove me bonkers. I tried securing and cushioning every single part of the vehicle that I could. It did make an improvement but the noise was still there.

Finally, I took out the entire interior, and with a friend driving I crawled over everything using a cheap stethoscope to try a pinpoint the noise.

I found it.

There was a somewhat large piece of loose plastic inside the passenger side side view mirror that would fly around banging into everything when the wind speed reached a certain level.

Replaced the mirror, problem solved. But this little story doesn't come close to imparting the hours wasted on this frustrating nuisance.

The moral? You may have to pull the interior and as a passenger  locate where the sound is coming from. It is amazing how things echo in the cavern of a vehicle interior. I was convinced it was interior trim in my case, nobody suspected the mirror.
.

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