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Old 12-11-2004, 06:36 PM   #1
PROSOUTH
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Default Moving C-3 Rear Frame Rails in to Narrow the Rear Frame Section?

Has anyone ever moved the C-3 rear frame rails in to narrow the rear frame section?

I haven't measured yet, but with the batwing mount of the '80 rear end it sits just inside and below the frame rails in my pictures. This would allow me to move the frame rails in about three inches on each side and put the mount for the batwing directly under the rail retaining the same location and relationships with the exception of having more 3 inches more of wheel well room.

I realize this would require removing a 6 inch a center section of the rear floor and moving the wheel wells in and inserting a 3 inch section in each wheel well.

I am doing a frame up on the new '80 this spring. Gotta make the designs this winter. On this car I am more comfortable making extreme modifications too. I was looking at the frame notch (mini tub) that several have used and wondered why not just move the whole rail in for a cleaner look and no notching. I really don't want put L-88 fender flares on my car, not that they don't look well on Corvettes, just not what I want. I am trying to put a set of 305's or so under the rear.

I need input on this idea, pro or con to save my a** later if this is a mistake. Thanks, Jim
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Old 12-11-2004, 07:00 PM   #2
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Where do you want to start moving them in? You can't start at the kickup, this would require modifying the entire underbody and the section of birdcage behind the seats. It would also mistplace the trailing arm pocket.

If you want to start further back it still leaves the rear body mount but that outrigger is easily lengthened.

I think if you clean up the frame and use offset arms like norval has (they are his own built items) and some other minor clearance work, you should be able to run 305s. You don't need a 12" rim for 305s, 10 would do easily.


If you really want to get creative, why not use a Ford 8.8 rear end, the batwing on those is much smaller than on ours and they have those nice viper axles available that are splined and slide, just like the ones on a toronado No messing about w/ c cips and ground down stubs.
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Old 12-11-2004, 07:15 PM   #3
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I realize the floor has to be modified to move the rear frame rail in. But why can't I move it in? I see removing the welds and sliding it in a couple of inches and moving the batwing mounts under the rail. The relationship of everything else is not disturbed. I have moved inner fenders inside before to meet the frame rail and I have mini tubbed G-bodies by cutting the frame rail and narrowing it then steel plating it for strength.

This would not move the trailing arm pocket or cross member, only the frame rail itself.

"If you really want to get creative, why not use a Ford 8.8 rear end, the batwing on those is much smaller than on ours and they have those nice viper axles available that are splined and slide, just like the ones on a toronado No messing about w/ c cips and ground down stubs"

Interesting, What is it from Explorer?

The frame rail is the limiting factor of wheel well space and the narrow batwing from the Ford will not help.

I have Van Steel Offset TA's already. The TA's will not move just the rear section frame rail that holds the batwing and the rear body mounts. jim
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Old 12-11-2004, 07:26 PM   #4
norvalwilhelm
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I have considered this same move but my battery boxes would have to be cut also. Where would I go with a battery?
As for cutting and moving them in will it interfer with the gas tank??
305 tires are possible without moving the frame rails.
Isn't the ford 8.8 found under all the mustangs? Is that the rearend Marck it talking about???
What it a batwing??
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Old 12-11-2004, 07:27 PM   #5
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Since I am not familier with the 80 rear end, but on the earlier ones I kind of came up with this idea. Remove the storage bins and do some fiberglass work. You want the half shafts and strut rods where they are. Throw some coilovers on like I have and also a tubular rear crossmember like mine. Move the frame rails in. Cut the trailing arm off and offset it, but don't offset it back, just have it go straight into the near mount that is in closer. Do whatever is necessary to the rear to make all that work and the body mounts. Just an idea, will it work though?
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Old 12-11-2004, 07:27 PM   #6
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Quote:
Originally Posted by norvalwilhelm
What it a batwing??
The mounting for the 80+ rear ends. That big wing thing that bolts to the diff.
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Old 12-11-2004, 07:50 PM   #7
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"I have considered this same move but my battery boxes would have to be cut also. Where would I go with a battery?"

I think there would still be room for the battery. I would only move the rails 3" max.

"As for cutting and moving them in will it interfere with the gas tank??"

I'm dropping a fuel cell in where the spare tire was to lower the center of gravity and the cell can be configured to meet available space.

"305 tires are possible without moving the frame rails."

I thought you had to notch your frame rails to do the 305's? I might be able to go larger than 305's, just a thought at this time.

"Isn't the ford 8.8 found under all the mustangs? Is that the rear end Marck it talking about???"

Yes it is an 8.8 carrier in the Mustang, but it is available in several mountings. One is for leaf springs and I have one for my Jeep Cherokee still on a skid from Ford with a Detroit locker, Disc brakes and 4:10 gears. I think the Mustang is a four link? mounting solid axel and apparently per Marck there is an independent rear suspension housing now. I was also unaware of this.

"What it a batwing??"

The aluminum mount for the rear chunk of an '80 - '96 Corvette

I have back halved a few cars and have a good friend that was on our drag car years ago that does chassis work for stock cars now. He be the one that will actually move the rails if the decision is made to go forward. I really think that it will work pretty well. This will allow all of the room I would ever need in the wheel wells for tires or slicks. It will also still have a stock frame appearance. jim
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Old 12-11-2004, 09:38 PM   #8
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I think what you'll end up doing, is slicing everything rear of the kickups off the car, installing a 2x4/4x4 square box between the kickups, and welding on to that for your rear frame!

No "easy" way in my eyes to just chop and move... Just do it like youre "Z'ing" a frame to slam the car.

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Old 12-12-2004, 02:08 AM   #9
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Click the image to open in full size.

Click the image to open in full size.

I can't get a power point to load properly so I will attempt to describe this procedure.

In the top picture you can see the bracket that holds the rear mount of the '80 located below and to the inside of the frame rails. Then you can see the rear frame rails as they are attached in the front at the crossmember. I see taking enough out of the inside rail supports to allow moving them in three inches and re-welding them in. Simple?

The hard part is going to be cutting and moving the floor pan around to allow clearance for the rails. I see removing 6" from the center of the rear floor and cutting again in the center of the wheel wells and moving those sections in and meeting in the center. Then put a 3" band in each wheel well to form a larger well. I will also make a 3" cut in each of the lower compartments to move the outside wall in to allowing the front kick-ups of the rails clearance for being moved inward.

If I cut the complete rear section completely off and reformed the rear frame area to allow the increase for the wheel well areas it would still look the same. The only difference is it would not be a stock rail placed there but a 4x4 tube stock and it would be welded in at the same place.

I think the shock of this is because no one has ever back halved a Corvette with original frame rails and used the independent suspension. The relationship of the suspension, attachment points or widths are not being changed. Just the location of the rails inward to add clearance.

I have an old Corvette I stripped a couple of years ago that has a good back section. I may go get it and bring it to the shop to play with this spring.

I know, y'all think I'm crazy, Jim

Last edited by PROSOUTH; 12-12-2004 at 02:11 AM.
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Old 12-12-2004, 08:12 AM   #10
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Personally I think you're nucking futs to go through all that just to house some 305s, I would go the norval route. Look what he's running on the back...305s if I'm not mistaking and everything looks stock.

Basically moving the frame rail will pose the following problems
* body mounts
* gas tank
* floor & storage boxes/battery box
* birdcage, and this I feel is really importaant, the area behind the seats will have to be severely modified without screwqing up the integrity of the roll bar behind your head, that whole thing gets it's structural integrity from the area that you will have to move inboard to clear the frame rail.
* shock mounts
* batwing mounts

If I was going to do it your way I would pull the body apart and take out the cage, then with proper spacers weld the cage to the frame, no more body mounts. Then modify the rear birdcage section to get the proper clearance, since frame and body are 1 now you will be able to tie stuff together to reinforce it. Narrow the rear end enough to use... C5!!! rear suspension, the a arms there need a frame clearanced in the way you want to do it so I would then just do that. A cradle for the suspension shouldn't be too hard to build. The 1/2 shafts would be the biggest problem most likely.

After everything is welded up & done have the entire thing powdercoated and then stick the fiberglass back on, patch up sections like the floor and rear compartment and presto
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Old 12-12-2004, 11:37 AM   #11
norvalwilhelm
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Click the image to open in full size. Putting a 305 tire is simple, the problem was when you run 12.50 x 28 ET streets, That is when I had to knotch the frame.
For 305's all you need is a slightly shorter spring , offset trailing arms and yes you can make them easily at home and the proper offset on the rims.
I was running 12.50 slicks under the fenderwell before.
As for frame rail to battery box clearance there is no 3 inches of clearance, cutting the battery box would be a pain, besides my battery takes up most of the area already.
NO I agree with twin turbo. It is not worth the effort to just run a small 308 tire.

Last edited by norvalwilhelm; 12-12-2004 at 11:40 AM.
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Old 12-12-2004, 02:56 PM   #12
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The tube frames that are available for these cars... I wonder if you could use their style attachment points... (Cant find a picutre) Maybe someone has a link?
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Old 12-12-2004, 03:09 PM   #13
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I think all the tube frames use c4, or c5 components.
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Old 12-12-2004, 03:09 PM
 
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