Frame Differences
Racer
Joined: Jul 2001
Posts: 363
Likes: 0
From: Winston-Salem NC
Instructor
Joined: Dec 2004
Posts: 236
Likes: 0
From: Clearwater Florida
It depends on your definition of minor.
The 74 and 79 frames are pretty much identical from the transmission cross member forward.
The shape of the side rails is different where they meet the cross member in fron of the back wheels. This may affect how the outside seat belts are anchored.
The bottom of the cross member in front of the back wheels is shaped different on the bottom to accomodate the differences between the exhaust systems on the catalytic converter cars.
The gas tank cross member is different.
The side rails from the kick-ups to the very rear is square on the 75-79 cars and recatangular on the 68-74 cars.
The rear cross member is the same on 68-73 cars.
The rear cross member on a 74 car is one year only.
The rear cross members on 75-82 cars are basically the same but will not interchange with 68-73 or 74 cars.
The 74 and 79 frames are pretty much identical from the transmission cross member forward.
The shape of the side rails is different where they meet the cross member in fron of the back wheels. This may affect how the outside seat belts are anchored.
The bottom of the cross member in front of the back wheels is shaped different on the bottom to accomodate the differences between the exhaust systems on the catalytic converter cars.
The gas tank cross member is different.
The side rails from the kick-ups to the very rear is square on the 75-79 cars and recatangular on the 68-74 cars.
The rear cross member is the same on 68-73 cars.
The rear cross member on a 74 car is one year only.
The rear cross members on 75-82 cars are basically the same but will not interchange with 68-73 or 74 cars.
Thread Starter
Racer
Joined: Jul 2004
Posts: 400
Likes: 1
From: California
so i guess what im really asking is since Kalifornia....er California has to smog anything 75 and up forever now, is there any way to drop a 74 from on a 79 body and have it work or would it be useless?
Instructor
Joined: Dec 2004
Posts: 236
Likes: 0
From: Clearwater Florida
The 74 frame will fit under a 79 body.
However you will have modification work to do on the:
1) Fuel tank mounting and fuel withdrawal system,
2) The rear bumper mounting,
3) Probably the outer seat belt anchors,
4) Probably the exhaust/muffler mounting.
5) You may even have modification work to do in order to mount the transmission.
1 and 2 will require a torch/sawzall, a welder, a grinder, and extensive metal fabrication work.
You can't just cut the back part of a 79 frame off and weld it to a 74 frame. They aren't the same shape.
The 74 gas tank is not the same size or shape as the 79 gas tank. The 74 fuel sending unit mounts on the bottom of the tank. The 79 fuel sending unit mounts on top of the tank.
3, 4, and 5 can probably be accomplished by just swapping parts.
If both cars are manual transmission cars, mounting the transmission and the drive shaft will be a breeze because both cars came with manual tansmissions from the factory.
If you want to run a TH400 automatic, mounting the transmission and drive shaft will be a breeze in the 74 frame because it came with a TH 400 from the factory.
However if you want to run a TH350 or someother automatic you'll need the transmission mounting bracket that will fit the corvette cross member and is specific to your tranmsission. You will also need the correct drive shaft. The 74 was not available with a TH350 and the 79 was not availabe with the TH400 from the factory.
It may be that the transmission tunnel area of the 79 will not fit around the TH400 tranny without some cutting and patching fiberglass work as well.
When swapping frames around its best to stick within the same family and even better within the same body style.
68-72, direct swap, no modifications required. TH400 available in all years.
73-74, rear cross member is different between these two years. TH 400 available in both years
75-77, direct swap, no modifcations required. TH400 available in all years. TH350 available in 76-77 only.
78-79, direct swap, no modifications required, fuel tank is larger than 75-77 cars. TH350 was the only automatic transmission available.
My advice would be if you want to end up with a 79 car, look for a 78-79 frame. If you go with earlier frames be prepared to do some parts swapping or frame modifcation work or both.
However you will have modification work to do on the:
1) Fuel tank mounting and fuel withdrawal system,
2) The rear bumper mounting,
3) Probably the outer seat belt anchors,
4) Probably the exhaust/muffler mounting.
5) You may even have modification work to do in order to mount the transmission.
1 and 2 will require a torch/sawzall, a welder, a grinder, and extensive metal fabrication work.
You can't just cut the back part of a 79 frame off and weld it to a 74 frame. They aren't the same shape.
The 74 gas tank is not the same size or shape as the 79 gas tank. The 74 fuel sending unit mounts on the bottom of the tank. The 79 fuel sending unit mounts on top of the tank.
3, 4, and 5 can probably be accomplished by just swapping parts.
If both cars are manual transmission cars, mounting the transmission and the drive shaft will be a breeze because both cars came with manual tansmissions from the factory.
If you want to run a TH400 automatic, mounting the transmission and drive shaft will be a breeze in the 74 frame because it came with a TH 400 from the factory.
However if you want to run a TH350 or someother automatic you'll need the transmission mounting bracket that will fit the corvette cross member and is specific to your tranmsission. You will also need the correct drive shaft. The 74 was not available with a TH350 and the 79 was not availabe with the TH400 from the factory.
It may be that the transmission tunnel area of the 79 will not fit around the TH400 tranny without some cutting and patching fiberglass work as well.
When swapping frames around its best to stick within the same family and even better within the same body style.
68-72, direct swap, no modifications required. TH400 available in all years.
73-74, rear cross member is different between these two years. TH 400 available in both years
75-77, direct swap, no modifcations required. TH400 available in all years. TH350 available in 76-77 only.
78-79, direct swap, no modifications required, fuel tank is larger than 75-77 cars. TH350 was the only automatic transmission available.
My advice would be if you want to end up with a 79 car, look for a 78-79 frame. If you go with earlier frames be prepared to do some parts swapping or frame modifcation work or both.
