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for those of you who read the above mentioned thread re:gas caps and tank vents....this is the retraction of that info...

the gas cap i recommended holds so much pressure now that it distorts the tank and the filler neck actually moves down at the end as a result of the tank distorting...
this is the same problem that jk aka
chev-hell reported...

i just noticed this today..the weather was warmer today so i guess this made the distortion problem show up that i didnt have experience when that thread was posted..

my parts guy told me that vented caps meant they let air in and pressure (over a threshold) out...not so apparently!!!!

so back to the drawing board!!!
my system has no vent so i dont know what to do to resolve the problem of pressure buildup in the fuel system???

getting frustrated with this one guys!!!!

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Rich
Cocoa Beach, Fla
Team Chevelle #380
46 but feeling like 20 when i'm in my 70 SS 454
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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I had the same problem with a MF tractor. Could not find a gas cap to replace it with. The one I tried would build up too much pressure and the tractor would die. I took a real small drill bit and drilled a hole in the cap and problem solved. May work on a chevelle to!!
 

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Rich how many hoses are on the front of the tank.Should be 2 one on each corner up high these should vent the tank.A vented cap will allow spillage under acceleration when the fuel sloshes to the rear.
On the other hand maybe the 70 doesn't have a charcoal canister. If thats the case I stand corrected...FRED

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I forgot the say that is not always pressure.I had a car that had a plugged vent cap that sucked the tank flat.Fuel out, air in...FRED

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My '70 Malibu, which I bought new in 1970, didn't have a canister, since it was sold in NJ. It came with a vented cap. During the oil embargo of '74/'75, I purchased a locking gas cap from a Gulf gasoline dealer which was non-vented. It wasn't too much longer until the bottom of the tank started sucking in!! A vented cap is necessary if you don't have the recovery canister under the hood. AND, yes, they DID leak if parked on a steep hill with a full tank! (like my driveway!!)

[This message has been edited by MalibuJerry350 (edited 01-30-2000).]
 

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Discussion Starter #6
fred, i know what your talking about but my tank ( new ) has no nipples wahtsoever...the only lines (2)come from the pickup assembly and run to the tank (fuel and vapor lines i am told)..is there a pickup available with a 3rd nipple that can be used as a vent???

MalibuJerry350...what about ender acceleration...did it leak then too??? certainly GM wouldnt produec a fuel tank system with these probs but you seem to indicate you bought your car NEW??!!!
how can this leaking vented cap be the original GM solution/design??




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Rich
Cocoa Beach, Fla
Team Chevelle #380
46 but feeling like 20 when i'm in my 70 SS 454
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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NOW. that i have a great understand of the inner workings of my gas cap
, my cap looked to be vented but didn't let pressure out so i took it apart and here is what i found..
there are 2 ways it can vent 1 way out has a large spring (that i cut in 1/2) and another small one for air to get in. i cut an reshaped the larger spring so it would still seal but would let pressure out at a LOT lower pressure than it was made for (obviously not our older cars
now i can blow thru it but its kinda hard but before i hurt my cheeks trying to. hope this works because bubbling a tank is scarry jk------------------
members.aol.com/jnkb2cool/chevelle9.jpg members.aol.com/jnkb2cool/350.jpg
John Krenn
1970 malibu SS look-a-like well kinda
307/200-4r (soon to be 355)

Ft.Worth, Tx




[This message has been edited by chev-hell (edited 01-30-2000).]
 

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Discussion Starter #8
fred, i know what your talking about but my tank ( new ) has no nipples wahtsoever...the only lines (2)come from the pickup assembly and run to the tank (fuel and vapor lines i am told)..is there a pickup available with a 3rd nipple that can be used as a vent???

MalibuJerry350...what about ender acceleration...did it leak then too??? certainly GM wouldnt produec a fuel tank system with these probs but you seem to indicate you bought your car NEW??!!!
how can this leaking vented cap be the original GM solution/design??




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Rich
Cocoa Beach, Fla
Team Chevelle #380
46 but feeling like 20 when i'm in my 70 SS 454
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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Discussion Starter #9
jk
how did you take gas cap apart??

mine is a stant and it has a rivit in the middle visible from the outside but not from the inside...
did you drill it out?? what did you use to reassemble??

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Rich
Cocoa Beach, Fla
Team Chevelle #380
46 but feeling like 20 when i'm in my 70 SS 454
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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Rich,
The cap never gave me a problem under acceleration, but if the tank was "topped off" and the car was parked on a steep hill, like my driveway, there would be seepage from the filler. My wife and I both bought our 70 Chevelles new a few weeks apart in May of 1970 and they both acted the same. The big problem is that in the summer, especially, the pressure builds up, the cap "vents", but some fuel seeps out. Depends how full the tank is and where the vehicle is parked. After a "fill up" I still back the car up the driveway instead, 500,000 miles later!
 

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