Gas Tank Vibration?

[Grabinov911]

Hey guys I have vibration coming from the rear of my 70 Roadrunner. It only occurs at low idle (after choke is off) or at idle in gear (say at a stop light). It is definitely a low frequency noise, like two pieces of sheet metal vibrating together.

I crawled under the car and started banging on things and I discovered that the noise can be replicated by banging on the right rear of the gas tank from the bottom. I checked the tank straps, and it is not coming from them. The tank is about half full and is a replacement tank from Classic Industries which I installed about 1 year (but only a few hundred miles) ago.

Is the noise coming from a vibration between the sheet metal top of the gas tank and the underside of the trunk floor? I'll admit that I re-used the old "mat" which goes on top of the tank and between the tank and trunk floor. It was old and I though it looked kinda cool (probably made of asbestos or some radical new material like that).

Anyone ever had this vibration? Do I need to drop the tank (ugh) - or maybe just shoot a little triple-expanding foam between the tank and the trunk floor?

 

[67 coronet]

if your not worried about it just try the foam.old pad prob got a rip in it.

 

[anmracing]

I'd have to agree. Never thought about using the foam but that probably work pretty good. We used some of the Dynamat style insulation and it works out pretty good.

 

[Photon440]

Are you able to feel the vibration from above through the trunk floor?

 

[6pktgo]

I`ve seen it were the pick up tube from the sending unit was just making contact with the floor of the tank. It was an aftermarket tank & sending unit & i don`t think the pick up tube was bent correctly or the mounting hole for the sending unit was not on the correct angle. Ended up pulling the sending unit & tweeking it a little. Problem solved.

If after you try the foam & it still vibrates, that`s where i would go.

 

[Hemi Rebel]

Check your exhaust real good. It may be making contact somewhere.

 

[72RoadrunnerGTX]

E.C.S. car by chance? Could be a loose internal vent tube. Most reproduction ECS tanks solder the tubes to the inside of the top half of the tank prior to seam welding the halves together. Solder joint may have failed with no way to get at it, tank replacement likely if that’s the case. I would apply some lateral pressure to the nipples, one at a time, see if you can still duplicate the rattle.

 

[Grabinov911]

Genious! I'll check all of those things. I don't actually know if the vibe can b felt from the inside - guess I need a buddy to bang on the bottom while I listen on top. I did think about the sending unit question so I filled up the tank, and the vibration is still there. I THINK this rules out the sending unit, but that was my first thought too (thanks 6pk2go). Never thought about the ECS tubes. The car IS a 70 California car with the 4 tank vent tubes and the strange trunk vent pipe. I think I looked for exhaust issues, but I'll go back and look at that too.

If I DO remove the tank, I'm go with "anmracing"s idea - Dynamat between the tank and trunk floor. I LIKE that stuff. Makes everything quiet!

Thanks gents

 

[6pktgo]

Don`t rule out that tank/sending unit just yet. :eusa_eh: When your buddy is there, have him hold the fuel line were it comes out of the tank and have him apply a small amount of pressure up or down & then you bang on that spot to see if either the vibration sound changes or dissappears or he can feel it vibirating as well. Only then would i move away from that thought.

 

[Grabinov911]

Got it. Will do... Thanks

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So please please bartender I want a six pack to go
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Well I don't have enough to pay my rent but I ain't gonna worry though
I've got time for one more round and a six pack to go