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I don't think you can correct the bladder. The one in my 78 was hard and brittle. And once liquid got between it and the tank all sorts of tiny leaks showed up. MHO just throw it out and get a new tank. You really don’t want to be messing around with gasoline and an old tank that isn’t going to get better with age.
If the steel of the tank is in good condition , you could cut out the bladder with a knife ( be careful its tough) and leave the edge around the opening as its the seal for the filler neck piece . That's what I have done when I welded a sump to the bottom of the tank . Leave the cap as is , it will still breathe through the charcoal canister as its designed to do
Obviously if the steels rusted , toss it all out and buy a new one , which wont have a lining .
You can certainly purchase a replacement tank. All Corvette vendors sell them as well as a number of other places.
The top of a 75-77 tank looks like this. (This one slightly modified for fuel injection).
the vent line from tank is the one in the center below the gas cap. See how it go's left to a T. Upper left above the T is the vent for the outside of the bladder. There is a small plastic restrictor in the end of the line to the bladder vent. Makes the hole much smaller, it's in there to help prevent fuel from going into the area outside the bladder, after the T off to the left, the line go's into the inside of the left quarter panel and then along the frame to the front of the car to the charcoal canister.
if fuel is getting into the backside of the bladder. First thing I would check is that vent line to the canister. Is it somehow blocked? Is the little plastic restrictor still in the vent line to the bladder? Is the rollover valve (in that hump in the top of the tank where the tank vent hooks up just below the gas cap). Is the rollover valve stuck open?
As I understand it. The bladder is in there for protection in the event of a crash. Lots of cars don't have one. I'm still running mine. One other thing to check. There is a "ladder " looking thing spot welded to the top of the sending unit door. It's there to keep the bladder from contacting the sending unit. Mine had fallen off and was laying in the bottom of the tank. You can see the weld marks in above photo from repairing it. I've heard others have had this problem as well.
You can certainly purchase a replacement tank. All Corvette vendors sell them as well as a number of other places.
The top of a 75-77 tank looks like this. (This one slightly modified for fuel injection). the vent line from tank is the one in the center below the gas cap. See how it go's left to a T. Upper left above the T is the vent for the outside of the bladder. There is a small plastic restrictor in the end of the line to the bladder vent. Makes the hole much smaller, it's in there to help prevent fuel from going into the area outside the bladder, after the T off to the left, the line go's into the inside of the left quarter panel and then along the frame to the front of the car to the charcoal canister.
if fuel is getting into the backside of the bladder. First thing I would check is that vent line to the canister. Is it somehow blocked? Is the little plastic restrictor still in the vent line to the bladder? Is the rollover valve (in that hump in the top of the tank where the tank vent hooks up just below the gas cap). Is the rollover valve stuck open?
As I understand it. The bladder is in there for protection in the event of a crash. Lots of cars don't have one. I'm still running mine. One other thing to check. There is a "ladder " looking thing spot welded to the top of the sending unit door. It's there to keep the bladder from contacting the sending unit. Mine had fallen off and was laying in the bottom of the tank. You can see the weld marks in above photo from repairing it. I've heard others have had this problem as well.
Thanks for a great explanation. Looks like I am going to wind up dropping the tank, which I was hoping to avoid.
I know many here kind of poopoo the bladder, but I think it is important and want to salvage it if possible.
When I drop the tank I will do an update here to let you know if I was successful.
Edit: BTW, I took off the canister line and drew vacuum through it. I could hear something sucking on the other end. So the line seems to be clear. I do want to check the smaller line and orifice. I want to pull vacuum through just the smaller line after the T and see what happens.
Interesting comment. I had my tank out recently. I was amazed at how clean it was in there! Absolutely no rust inside a Bladder. And my 40 plus year old bladder was in amazingly great condition. These things never see sunlight. I too like the idea of the bladder.
also, pulling the tank is really very easy. Pull out your spare tire carrier and the top cover of it. I had to lossen the left exhaust so I could nudge it a little to the left, but I didn't need to remove it. Unplug the sending unit wires in the left quarter panel. Loosen The strap bolts at the rear crossmember. Remove The forward member. Tip it down towards the front of the car. When you get it to about 45degrees. You can reach in and undo the fuel lines and vent line. Then out it comes.
Just thought I'd add. It's perfectly O.K. if the bladder moves. You started this thread with asking about a collapsing Bladder. The reason they put the ladder type guard in there to protect the sending unit, and the reason for the vent line for the outside of the bladder is because they knew it would move around. This is not a problem. It is the design of the bladder.
see this "ladder " looking guard inside the tank attached to the lid of the tank/fuel sending unit. Ignore the electric fuel pump. First photo shows std. Setup.
Chevrolet put that guard in there because they knew that the bladder would move. When you fill the tank, the vent on the outside of the bladder allows the air to escape and the bladder to form to the walls of the tank again.
When everything is working properly.
I personally think that the bladder is great. No matter how much the tank might rust. No rust in the fuel and no leaks. Somehow I find this to be a good thing. Not to mention it's intended purpose. Protection of bursting in a crash.
So yes, I think you do need to drop your tank. Pull the sending unit. Check the vent lines and make certain your bladder is in as good of shape as mine.
Me, I don't run a charcoal canister. My tank vent terminates just in front of the rear wheel. Some worry about fumes. I've never had an issue. And I've run it this way for over 20 years.
getting fuel on the outside of the bladder is an issue. Collapsing is not.
Last edited by 4-vettes; May 17, 2020 at 05:11 AM.
True indeed and I just had that done on my 78..
Most vendors offer the tank etc as a whole package and some you have to purchase each par separable..
FWIW I even have a few essential parts left over..
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Originally Posted by 4-vettes
Me, I don't run a charcoal canister. My tank vent terminates just in front of the rear wheel. Some worry about fumes. I've never had an issue. And I've run it this way for over 20 years.
I still have all the plumbing for my charcoal canister but the vent tubing from the canister to the carb has been plugged for 25+ years. Car is always parked inside my garage. Not a whiff of fuel ever. It's an emissions system that really is not necessary anymore for classic cars unless their are concerns for minute amounts of gas evaporating in the gas tank into the atmosphere. EGR valve also not necessary. If a car does not need to meet any emission systems regulations, then why spend money to fix them? Unless of course it's for originality.
My 75 did the same think and yes it is not repairable. To many years to go any longer pulled bladder tank damaged. Installed new bladder less Tank all is well.
Fuel tank bladder
