Surprising frame incompatibility

[denpo]

As you may know, I'm currently swapping my '76 to a better frame from a '75 (it's a '75, right Tom?)
Upon reinstalling the gas tank I discovered the cross member gas tank support is not located a the same place.
On the '76 this support it 12" away from the end of the frame, on the '75 it is 15" away.
But when I look up on vendors' site, they list my '76 tank (the one with the big oval hole) as a '75-'77 Tank.
I'm confused.
The two frame are definitely from the same year bracket, has they share the same back bumper round holes for the hydraulic shocks absorbers.
I looked at the only corvette frame comparison webpage I know http://www.71corvette.com/frames.html
And it claims the change in the tank support location is supposed to happen in 78, which seems bogus, since '78 frame have square shock holes.

With the support crossmember pushed away 3" further the gas tank is not supported anymore.
I guess those things happens when you don't use same year frame, and it can be fixed by making new holes in the frame, but would have like to more about it.

 

[mrvette]

I dunno man, all I can say there is no two of nuttin' come off a assy line identical since WW2 man.....

:gurney::bestwishes:

 

[BBShark]

Is there a serial number on the frame? That will tell you what you have.

 

[Tom Sarno]

Denis,

I was told it was a '75 frame. I have the tank that I think is from that frame. Is the problem the tank is narrower front to rear? I will take a picture and measurements in the morning.

Tom

 

[denpo]

Denis,

I was told it was a '75 frame. I have the tank that I think is from that frame. Is the problem the tank is narrower front to rear? I will take a picture and measurements in the morning.

Tom

Yeah, my tank is narrower.
It has the big oval hole, like this one :
http://www.zip-corvette.com/_Images/Blobs/GT-349.JPG

Only 75-77 are supposed to sport such a tank.
I still have to hunt down the frame serial number.

 

[Twin_Turbo]

Yes, that's the 75-77 bladder tank. The 78-82 tanks have a round access hole for the pick up tube/level sender (and fuel pump hung from it in 82), the later tanks are plastic w/ a steel outer case. Not a soft bladder like the above one.

The frame serial number is on the dr. side rear kickup, near where the shock tab is. (but on the top surface). However, it's probably only a serial#, no year distinction in it most likely.

 

[enkeivette]

Time to bust out the angle grinder and the welder.

 

[denpo]

The frame serial number is on the dr. side rear kickup, near where the shock tab is. (but on the top surface). However, it's probably only a serial#, no year distinction in it most likely.

Searched hard for it, but serial # is nowhere to be found.