Help diagnose this noise please. - Chevelle Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 11 (permalink) Old Jul 4th, 19, 6:54 AM Thread Starter
Simon
 
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Help diagnose this noise please.

Got a noise coming from my 66\327 SBC that I can't pinpoint. Sounds like it is coming from the back of the engine or around the flexplate/transmission inspection cover, and is loudest on the drivers side. Thinking maybe its a exhaust header gasket, flexplate issue or potentially inside the engine. Car drives ok, can't hear the noise in the interior when driving, but concerned it could get worse in the long run.

Video is in the link below, I tried to capture the sound best I could.
https://1drv.ms/u/s!ArAK8basDQk6sT8yoWKGgDArdakl

I have done the following:
Checked for exhaust leaks where the headers meet the exhaust, fixed this with a new exhaust gasket. Sound still there
Tightened headers bolts all the way in
Removed rocker cover and looked for obvious play/movement in any components, can't find any.
Jacked up the car for any noticeable damage, none found. I can see the flexplate spins freely when the car is running.

Any idea? I think next I will try a new header gasket, if that doesn't work maybe remove the rocker cover and crank the engine to see if the rockers move like they should.
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post #2 of 11 (permalink) Old Jul 4th, 19, 9:24 AM
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Don
 
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Re: Help diagnose this noise please.

Sure can't hear anything in the video? What type of noise,knocking,rattling,scraping? Usually a flexplate issue will change when trans is put in gear/loaded,have someone do that for you while you listen underneath,exhaust noises usually sound different under load also.
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post #3 of 11 (permalink) Old Jul 4th, 19, 6:19 PM Thread Starter
Simon
 
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Re: Help diagnose this noise please.

Quote:
Originally Posted by Don B View Post
Sure can't hear anything in the video? What type of noise,knocking,rattling,scraping? Usually a flexplate issue will change when trans is put in gear/loaded,have someone do that for you while you listen underneath,exhaust noises usually sound different under load also.
Thanks Don, its more of a rattle I would say, seems the loudest when listening from next to the wheel well or underneath the car. I'll try to listen once it is under load, good idea.
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post #4 of 11 (permalink) Old Jul 5th, 19, 9:57 AM
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Jeff
 
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Re: Help diagnose this noise please.

An easy way to find exhaust leaks without burning yourself, get a shop vac, put the hose on the output side of the vacuum, shove the hose into the tailpipe and seal it with shop rags. This will pressurize the exhaust pipe. I usually try to put the vacuum outside of the garage and close the door as much as possible to block the sound. That way you can feel for air leaks and know you're on it when your finger passes over it as the sound will change.

I'd recommend doing that before just going crazy on replacing gaskets. Do you see soot marks anywhere on the spark plugs, boots, head?
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post #5 of 11 (permalink) Old Jul 5th, 19, 10:51 AM
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Re: Help diagnose this noise please.

Wife's Cadillac had a rattle at the front of the engine whenever the A/C was on. I figured it was the idler pulleys so I replaced both of them. Rattle was still there. Took it to our local Cadillac dealer who pronounced the A/C compressor was bad. After replacing the compressor, still had the rattle. Service advisor had one of his long time mechanics look at it. He put it on a lift and found the flex plate was cracked.
I guess it goes to show that an unusual noise can transmit itself to different areas making an accurate diagnosis somewhat difficult.
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post #6 of 11 (permalink) Old Jul 5th, 19, 12:38 PM
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Hank
 
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Re: Help diagnose this noise please.

You don't have a blown out tube on the header do you. Check the tubes for holes.

71 Malibu, Cottonwood Green, 396 BBC, AutoGear M22W 4 speed, 12 bolt 3:55 posi.
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post #7 of 11 (permalink) Old Jul 5th, 19, 12:52 PM
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David
 
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Re: Help diagnose this noise please.

Run 'er till she smokes!


later, dozer

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post #8 of 11 (permalink) Old Jul 5th, 19, 4:57 PM
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Randy
 
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Re: Help diagnose this noise please.

Check for header leaks where the 4 exhaust tubes are welded into the collector. I had one years ago that leaked at this junction.

Randy
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post #9 of 11 (permalink) Old Jul 6th, 19, 3:02 PM
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Eugene
 
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Re: Help diagnose this noise please.

I would drop the cover on the trans and check for a cracked flex plate. Seen it many times.
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post #10 of 11 (permalink) Old Jul 6th, 19, 9:09 PM
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Gary
 
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Re: Help diagnose this noise please.

Quote:
Originally Posted by Bonkerman View Post
I would drop the cover on the trans and check for a cracked flex plate. Seen it many times.
Also check the bolts on the flex plate, I was doing a cruise a couple years ago, and every time I was next to another car, it sounded like that car had a serious rod knock, I figured it had to be mine since several other cars all sounded the same. Got it home and it was discovered that the flex plate had come loose and when the car was at a low RPM the flex plate was slapping around on the bolts.
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post #11 of 11 (permalink) Old Jul 6th, 19, 11:29 PM
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Re: Help diagnose this noise please.

I had a cracked flexplate no noises but it caused a vibration at a certain MPH and caused the front trans seal to leak.Above or below that MPH it was gone but drive around at 45 to 50 it was always there.

PS:How come everyone who posts a sound bite for us to listen to a noise, posts a sound bite that's only around 10-15 seconds ?
Whats wrong with 30 or 45 seconds ? it might make it easier for people to pick up the noise before it shuts off.

John
71 El Camino SS
406 SBC M21 3.31 12 bolt
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