DaBo

For the owners of 75-77 Vettes who are having fuel fill and/or mileage range problems......This is for you!!!!

I have owned my 76' for almost 4 years. After about the first year and a half I started to have problems with fuel range from a full tank of gas. One day I ran out of gas even though the gauge read that I had a half tank. I got to the station and filled it up but it only took about 5-6 gallons.
I did some research and found that in 76 GM put heavy rubber bladders in the tanks. Over the years these bladders would collapse and you could not fill you tank to full capacity.

I drove mostly in town so I let it go and figured out that I could get about 100-120 miles from a tank and then "fill" it back up. Usually took 4-6 gallons per "fill".

This past weekend the wife and I took both Corvettes to Kansas City for the Hot Rod Power Tour. All was fine until the trip home. We had only gone about 30-35 miles on the last "fill" and the 76' ran out of gas.

Today, I dropped the tank in the 76' and this is what I found. Exactly what I had expected, the bladder had completely collapsed and was stuck onto the float for the gauge.
I knew almost 100% that this is what I would find but I just put off doing anything about it.

Now, I am able to pass this info on to any others that are having the same problems, but did not know what was wrong. I do not remember all the years that the liner was used. It may have started in 75. I am sure other members will share there experiance with these gas tank problems and solutions.

I am going to have the tank spray lined on the inside then reinstall it.










[Modified by DaBo, 11:24 PM 5/29/2002]

Markm10431

Grat info! Thanks from a newbie who would have paniked

terryrudy

Added to Corvettefaq.
thanks! :)
-terry

norvalwilhelm

My 75 had the bladder but I removed it when I install dual 1/2 inch pickups in the bottom of the tank. The inside does not need to be coated. It is finished like any other tank and I have never had a problem with the uncoated tank.

Kenzy

Thanks, I'm having a similar problem and will be dropping the tank in the next couple of weeks.

DaBo

Norval,

Thanks for that info.
I took my tank down to a local shop that specializes in this kind of thing.
He gave me two options. First, use some heavy duty adhesive to bond the bladder to the tank. Or, leave it as is. After looking at it he said that it was as good as a new tank. He was very impressed for the age. He wanted $125.00 to line it. I didn't want to take the chance with an adhesive, so I left it as is and bolted it back in. Glad to hear that you have not had any problems with yours.

:cheers: :cheers: :cheers: :cheers:

SteveG75

When I pulled the tank out last winter, my bladder was still in good shape so I left it installed. Average about 15 gal to fill from E on the gage. Never run out of gas yet (I think I just jinxed myself).

Interestingly enough, my owners manual states that if left unfueled for a long time, the bladder could collapse. It recommends that for long term storage, that the bladder be removed, coated with a light oil and stored in a cardboard box. :crazy: No reference however in the owner's manual that it is a total PITA to get the tank out of the car. :rolleyes:

Matt Gruber

in 1977 my friend got a then brand new 77. We took a trip, and we had a good laugh; the gauge kept going up the farther we went :crazy: Then i said: WE BETTER STOP AND DRAIN OUT ALL THE EXTRA GAS :lol: So we stop for gas knowing it HAD to need some even tho it said FULL. So Harry unscrews the cap and GAS SHOOTS OUT :crazy: .
hARRY, ARE YOU IN THIS CLUB?

Cookwithvette

Thanks for the info. I've had similar issues with my 75 but when I looked in the tank I couldn't make out what I was looking at. I had no Idea these bladders could collapse.

I'm going to regret saying this for sure but, I'm pointed in the right direction now. :cheers:

DaBo

Just to update.........

Filled the 76' with gas this afternoon. Just over 18 gallons!!!!! Most gas I have EVER put into it. Took a trip across town. Good news, NO LEAKS!!!!

R. Bruno

Thanks DaBo. I never get 18 gals. in my 76. More like 13 so I know the feeling. What a dumb idea this bladder was!!!

jwatty

Thanks for the info. My 82 which should hold 23.7 gallons only holds 15 gallons from empty to full. I recently asked the same question on this forum and got answers similar to yours ... thanks for confirming.

Paul Borowski

Went through all this back in '94, when coming back from the Corvette Museum Grand Opening, my '75 kept taking less and less fuel every stop on the way home. As I got home, the bladder had deformed so much it was completely against the opening for the fuel!!! I could'nt even push my finger through it. That material is pretty thick, for anyone that has seen this stuff out of the tank. Before I had my real trouble, my '75 would only hold 12.5-13 gallons of gas when nearly empty. I wrote an article for the NCRS Driveline last year on how I removed the bladder. Now, it'll take a full 17.5-18 gallons of fuel. I drove a '77 down to Asheville, NC a month ago, and after 200 miles the "low fuel" light came on(fuel needle all the way down to empty). Stopped for gas, and it only took 12.8 gallons!!! The "bladder" in that car too is "collapsing". You'd think the weight of the fuel would keep the bladder "pressed" against the sides of the tank, but it DOES NOT!!! You do not have to "seal" the tank, as it's just like a '70-'74 tank that does'nt have a bladder. Also, '78-'82's won't have this problem. Their tanks have some kind of "rigid" fiberglass or hard plastic liner, not pliable/flexible rubber bladders like the '75-'77s had. :yesnod:

DaBo

I had seen the year breaks for the bladder and non bladder tanks, but could not remember it when posting this morning. Thanks for the additional info.

bob

On a friends 76 we had the same problem while on a trip. We put a vented cap on and it worked fine for the rest of the trip and for a few months later until he took the tank out and fixed it. I guess when the liner comes loose, as the fuel is used it sucks the liner in if there is an unvented cap on. Then when you fill up it doesn't always go back in place and you don't get a full fill. What is the cap supposed to be on a 75-76, vented or not vented?
bob

Paul Borowski

bob, the tank(cap) is non-vented. Was this way since '71? The vapor or vapor fumes and pressure were designed to be "vented", "purged" or "recycled" through the "carbon canister", below your windshield washer fluid reservior. This is where the fuel tank vent line that exits the left side of the fuel tank runs along the main rear brake line goes to(carbon canister). :seeya

bob

I guess that is why my friend sucked the bladder in as he had a unvented cap on it to start with. Thanks for the info.
bob

jwatty

If the 78-82 do not have the rubber bladder then why would a 23.7 gallon tank only hold 15 gallons?

Paul Borowski

I myself have never ever heard of a '78-'82 having this problem. Was my understanding when I read up about '78-'82 tanks, they had some kind of rigid, fiberglass? plastic, non-pliable(bendable)liner as the '75-'77's had. If there is something happening like this in that tank, you may be able to see what is happening with a small flashlight and one of those "small inspection" mirrors like we use in NCRS judging. Would be interesting to see if the same thing maybe happening to '78-'82's in the future???

Ben Taylor

My 81 is also supposed to have a 23.7 gallon tank, but it only holds 12-18 gallons.