Weird harmonic drone/vibration at ~2200RPM.
#2411509
11/30/17 11:06 PM
11/30/17 11:06 PM
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Joined: Jan 2004
Posts: 877 Pittsburgh, Pa
Jeff_383
OP
super stock
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OP
super stock
Joined: Jan 2004
Posts: 877
Pittsburgh, Pa
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I have this very annoying drone/vibration at 2200RPM. It sounds through the exhaust, but hard to nail down. It's in drive/driving and (a very slight lesser degree) in park too. It reminds me of a driveshaft that's out of balance/pinion angle off. That type of on/off drone. The car runs/drives excellent. In fact best it ever has, except this drone. Goes away as soon as it goes above/below that rpm. I'm pulling my already bald head hair out!
...It's a stroked 400/727/8.75 and a 67 Coronet.
Last edited by Jeff_383; 11/30/17 11:07 PM.
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2411522
11/30/17 11:16 PM
11/30/17 11:16 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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Same place, same RPM every gear? Or same place, same MPH every gear?
Boffin Emeritus
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2411615
12/01/17 01:23 AM
12/01/17 01:23 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Check to see if your balancer is tight on the crank(not a loose fit)..pull your belts off and try it
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2411760
12/01/17 01:44 PM
12/01/17 01:44 PM
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Joined: May 2003
Posts: 6,561 Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,561
Downtown Roebuck Ont
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That sounds like a bearing to me.
Will it do it parked and held at 2200?
If so it's engine or input side of the transmission related.
What does it do if you run it past that speed on the road, put it in neutral and let it coast back down?
If it does it then it's probably a tailshaft bushing or a wheel bearing if it's the kind of vibration that I think you're describing.
Kevin
Last edited by Twostick; 12/01/17 01:47 PM.
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2411761
12/01/17 01:54 PM
12/01/17 01:54 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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I suspect some resonance in the exhaust system. For a test, try hanging some weight on the clamps (small bar bell using bailing wire) - if it changes that's it. The cure may be as simple as moving a clamp, adding a clamp, or weakening a clamp (making it more flexible). Last: move your X-over or push the mufflers back a bit.
Boffin Emeritus
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: polyspheric]
#2411765
12/01/17 02:01 PM
12/01/17 02:01 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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I suspect some resonance in the exhaust system. For a test, try hanging some weight on the clamps (small bar bell using bailing wire) - if it changes that's it. The cure may be as simple as moving a clamp, adding a clamp, or weakening a clamp (making it more flexible). Last: move your X-over or push the mufflers back a bit. I believe its in the exhaust also... add any weight to it and see if it changes the rpm point
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2412178
12/02/17 12:09 PM
12/02/17 12:09 PM
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Joined: Jun 2016
Posts: 170 Wisconsin
Medlock51
member
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member
Joined: Jun 2016
Posts: 170
Wisconsin
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Do you have Drone (Flow) Master mufflers?
Last edited by Medlock51; 12/02/17 12:10 PM.
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Re: Weird harmonic drone/vibration at ~2200RPM.
[Re: Jeff_383]
#2412216
12/02/17 01:23 PM
12/02/17 01:23 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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If all else fails, you may have a short straight section of both pipes (but may not be in the same place) where you can insert an "empty bottle": a 3" ID X 6" can to change the resonance by adding another frequency.
Boffin Emeritus
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