SwampeastMike

'79 L82

I get a really loud buzzing/resonance in the rear with the tach between 825 and 900 or so. It seems like it may be coming from the cargo shade but happens with the shade in any position.

Anyone else have this problem and discover the culprit?

Shark Racer

That's literally like right off idle. Are you sure your tach is correct?

I can find some bad resonance in the 1500-2000 ish range with my car, but that's more normal for these engines.

SwampeastMike

Yes, it is JUST above idle and occasionally at idle.

vbgod1

Dunno how big ya are, but can you get back there and look for it while someone else drives?

SwampeastMike

Despite my size (6'3", 260#) I did just that and nothing I touched stopped it. The only things I know for certain are the narrow RPM range when it appears and that it's coming from the inside rear. With that big glass window it's very difficult to discern the exact location even though it [seems] to be coming from the very rear.

vbgod1

How about a stethoscope, looking for where it is loudest?

SwampeastMike

Do have a stethoscope but hadn't thought of that. I will say though that it is a VERY loud noise and amplifying it may be unbearable.

Shark Racer

Any loose muffler hangers or possibly a blown muffler?

Revi

I had a fuel filler door drive me nuts thinking the noise was coming from "inside" of the car.

DUB

YES...I am aware of the noise and where it is.

I have had it literally be the handle on the sun shade.

I have had it be the black panel that surrounds the bottom of the rear glass.

I have had it be the factory rear speaker mounts.

I have had it be the drop-in storage compartment behind the passenger seat...and loose spare tire jack and wrench....and also loose electrical components that bolt to the back side of the rear panel behind the seats.

I have had it be the spare tire carrier and parts inside the spare tire itself.

The fuel door can do this...

DUB

Rky Mtn C6

I had the same thing and it was the shade roller. A temporary fix was to stuff a rag of the same color as my interior between the roller and the area it was vibrating against.

HBZ_81_C3

I had the same issue. I found mine to be the rear speakers/mounts as DUB stated above. I had aftermarket speakers installed on the factory speaker mounts. The larger diameter magnets on the speakers was making contact with the metal panel behind the speaker.
Pull the rear speakers out and see if it goes away.

SwampeastMike

Thanks all!

I can't be the original rear speakers/brackets as they are in my storage room The speakers I have back there until I figure out what sort of enclosure to build and I just move the out of the way when trying to locate that buzz.

I don't have either either a jack or wrench. The spare (an original) is in my garage--why lug it around when it wouldn't be safe for use?

Mufflers/piping seem nice and secure but I haven't gone over them with a fine-toothed comb.

All the electrical components inside the cabin are nice and secure.

I've definitely thought of that black panel that surrounds the glass but pressing on it in different locations neither stops the sound nor lets me feel the vibration.

Gas tank lid... Interesting... Will investigate but doubt it as if it were that loud inside the car it would be insane outside the car.

Sun shade handle... Will double check.

Sun shade mechanism... That's my suspicion but even when I replaced the carpeting, repainted all of that black trim around the rear window, removed the original speakers/brackets, etc. I didn't remove that mechanism as it works fine and the way to remove seemed far from obvious.

Where's a small wiry teenager when you need one? None in my nearby family.

SwampeastMike

Sorry all. I forgot to mention that this problem is intermittent.

As best I can tell it is temperature dependent and is most obnoxious between say 75F and 85F ambient and becomes insane on comfortable, sunny days--a rarity here in southeastern Missouri.

During my 5-mile drive yesterday the weather was glorious but the buzzing was hideous. Today it's cloudy and cooler (60s) and the noise refuses to appear!!!

DUB

OH BOY...I see that this is going to be total joy in finding. Nothing worse than an intermittent issue.

Is your spar tire carrier installed? I know you do not have a spare tire...but if the lower housing is installed...and not being held tight with the tire pinching it ...it may be making that noise.

DUB

mortgageguy

Does the 79 have the chrome trim rear lisence plate bezel? That became loose on mine and caused a vibrating noise when idling.

john 72-04

Many years ago I had a tool that was called chassis ears. You would clip sensors at different locations throughout the car that would go to a base unit with a dial on it that switched to all the sensors. Get the car making the noise and rotate the **** until the noise was most prominent note which sensor it is and start looking in that location. Maybe someone at a local shop would possibly have this tool or something more modern that could help you locate your noise.

SwampeastMike

Good idea!

No license plate bezel in '79--the plate just insets into the "rubber" bumper. BUT I have heard nasty buzzing noises near idle with eight cylinders (no matter how smooth) from license plates.

SwampeastMike

you got it!!!

There is nothing worse to diagnose and correct than an intermittent issue!!!!

terry82

https://itunes.apple.com/us/app/matc...949048816?mt=8 there are others that you can buy, but this gives you the idea.amazon should have several to choose from