When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I purchased my 1976 in November and I've only ever been able to put 12 gallons of gas in it, so my bladder is collapsed. It has always been the same 12 gallon capacity. Does this mean that I have 4 gallons of old gas outside of the bladder?
I'm assuming if it was air taking up the space outside the bladder, the volume would vary. If it is 4 gallons of gas outside of the bladder, could that mean there is a hole in the bladder?
My car came with an MSD Atomic EFI and an external PWM fuel pump mounted on the passenger rear frame rail that pushes 45 pounds of pressure. I wonder if that higher pressure being pulled from the tank helped to collapse the bladder.
The connector from the charcoal cannister to the manifold is cut. Did that contribute to the bladder collapse?
I've read several threads including by @4-vettes about keeping the bladder, cutting out the bladder or buying a new tank. Are there any safety issues with cutting the bladder out and using the old tank? I've read several posts that say the bladder is not needed in newer models, but ae there any construction differences in the stock tank that make it less safe or reliable without a bladder?
A new tank is not very expensive. Should I just buy a new tank? Should I pull the tank and try to get the bladder to fully expand, but what would keep it from collapsing again?
Apologies for the multiple questions. I appreciate everyone's insight and advice.
my 78 OEM had a bladder. It was hard plastic. It developed a leak and I decided rather than fix and cross my fingers ( still not sure how to fix that) and since I had already dropped the tank, I bought a new one. It was not very expensve.
GM first started using the tanks with a bladder in then in 75, marketing them as a safety feature. GM also added a shield around the tank in the 70's. This was about the time the media first started carrying on about exploding Pinto gas tanks, and maybe about the time the NHTSA started making noise about tougher regulations on fuel tanks. Whether the bladder make the Corvette safer is open to debate, but something is better than nothing. Tanks leaking around the inlet I think have been found to be more likely to leak and cause fires in a collision, then the tanks themselves. The Corvette's filler being located in the top of the tank makes it much safer and less likely to leak in an accident then the rubber hose connected rear or side mounted filler necks found in most cars of the 60's and 70's.
If the bladder collapsed it's usually because it's developed a leak allowing fuel to become trapped between the bladder and the tank. The leaking bladder's have been a common problem with 75-77 and 78-82 Corvette tanks for quite some time. There use to be a replacement bladder available for 75-77 tanks, but I haven't seen them offered in a while. I'm not aware of any way to patch or seal a tank bladder and have to think that if your 48 year old bladder started leaking in one spot, patching it wouldn't guaranty it wouldn't develop another leak somewhere else in the bladder.
If you're going to go to all the trouble to drop the tank, I can't imagine putting the old one back in. Years ago radiator shops use to repair and seal coat the inside of old gas tanks, but this was usually something we did for old cars that replacement gas tanks weren't available for, forcing us to have to reuse an old tank.
Since you tagged me, thought I'd reply. Yes, I still run the factory bladder with no issues.
Before I would spend any money I would pull the tank you have now and investigate. You seem worried that perhaps you have a hole in your bladder. Yet you haven't confirmed this. And the fact that your capacity hasn't ever changed makes one wonder about that.
There is a vent that allows air to escape from between the tank and the bladder. If that became plugged. Air would be trapped. And it would be a very simple fix.
Dropping the tank out is not a big job. Not at all.
No the fuel pump didn't collapse your bladder. The pressure is on the line to the throttle body. Not in the tank. The Carcoal canister has been disconnected on many, many cars. Including mine. With a intank pump.
perhaps drop the tank out. Take the top off and have a look. Stop guessing.
There is a vent that allows air to escape from between the tank and the bladder. If that became plugged. Air would be trapped. And it would be a very simple fix.
Dropping the tank out is not a big job. Not at all.
No the fuel pump didn't collapse your bladder. The pressure is on the line to the throttle body. Not in the tank. The Carcoal canister has been disconnected on many, many cars. Including mine. With a intank pump.
perhaps drop the tank out. Take the top off and have a look. Stop guessing.
@4-vettes as always, I appreciate your insights. I've already ordered a new tank, but if the old one looks good, I could always return it.
While I wait for the tank arrive by next weekend, could I put my mity-vac vacuum pump/gauge on the line to the charcoal canister and see if it flows freely? If it does flow, it could also be a leak between the charcoal canister and the tank, but if it holds a vacuum, then the vent line is likely plugged, right?
Your tank is fine, with or without a charcoal canister.
your idea of putting vacuum on the line won't work. On the top of the tank, the vent line has a T. One line goes to the roll-over valve to vent the tank, the other T's off and goes to another fitting that vents the outside of the bladder. There is a small plastic retrictor in that line. To prevent fuel from entering the side of the bladder. No, your best bet is to drop it out and check everything. It's a really easy job on jackstands.
The spare tire carrier can be a pain. The bolts holding it to the crossmember were rusted. Suggest getting up there with some PB Blaster a day or so before work. I never reinstalled it.
The spare tire carrier can be a pain. The bolts holding it to the crossmember were rusted. Suggest getting up there with some PB Blaster a day or so before work. I never reinstalled it.
good advice. I will blast it with penetrating oil tonight.
I was able to remove the tank yesterday. I have the car up on Harbor Freight ramps with jack stands under the jacking points for added safety. All of the bolts turned easily and I found very little rust underneath the car.
The bladder looks fine, and it wasn't collapsed, but given the 12 gallon capacity, I am not going to mess with the old tank anymore.
When I pulled the tank I realized I need a new sock for the fuel pickup tube. It turns out the 1975-77 sock has the inlet on the side / top instead of the end and this sock is no longer available from most vendors, but I posted another thread and got several recommendations on where to find an NOS unit. I ended up ordering a GM part number 561723 on eBay and hope to receive it mid-week.
The front side of the bladder is slightly oxidized and noticeably loose from the tank wall. $7 siphon pump zip tied to a hanger to reach bottom of the tank No build sheet.
04-27-2024, 08:54 AM
My 76 12-gallon bladder gas tank. Fix or replace?
ve.
