Front Sub Frame - Bend or Break
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Joined: May 2007
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From: Santa Clarita CA
Front Sub Frame - Bend or Break
Hello,
I am working to putting back together a C6 base that had some forceful unplanned bodywork done to the front end (:cough: an accident :cough: )
Passenger frame rail was bent, and it was bent straight up. Replaced the frame rail and measured everything 12 times it felt like and it measures within 1mm in every direction, and left matches right as well.
Went to put the drive train back in last night and front sub frame is not lining up with the mounting bolts in the frame rail (probably off by about 3/4 of an inch
)
After calming down that the frame rail was in the wrong place, and remeasuring the frame rail, which still is measuring within 1mm) and matching top and bottom no matter how i measure, i started looking at the sub frame.
If i measure from rear mounting hole on front sub to front mounting hole on the rear, the left is off by roughly 3/4 of an inch
found the problem....
Now the question, my understanding is these sub frames are aluminum, and aluminum likes to crack and not bend. I do not see any cracks, or bends, to the naked eye it looks as straight as an arrow. Is it possible to have a bent sub frame, and have no stress lines, cracks or wrinkles?
I am working to putting back together a C6 base that had some forceful unplanned bodywork done to the front end (:cough: an accident :cough: )
Passenger frame rail was bent, and it was bent straight up. Replaced the frame rail and measured everything 12 times it felt like and it measures within 1mm in every direction, and left matches right as well.
Went to put the drive train back in last night and front sub frame is not lining up with the mounting bolts in the frame rail (probably off by about 3/4 of an inch
)After calming down that the frame rail was in the wrong place, and remeasuring the frame rail, which still is measuring within 1mm) and matching top and bottom no matter how i measure, i started looking at the sub frame.
If i measure from rear mounting hole on front sub to front mounting hole on the rear, the left is off by roughly 3/4 of an inch
found the problem....Now the question, my understanding is these sub frames are aluminum, and aluminum likes to crack and not bend. I do not see any cracks, or bends, to the naked eye it looks as straight as an arrow. Is it possible to have a bent sub frame, and have no stress lines, cracks or wrinkles?
Last edited by Hellbringer; May 3, 2017 at 11:01 AM.
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Joined: May 2007
Posts: 50
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From: Santa Clarita CA
I am pretty sure mine is aluminum, I use magnets to locate centers of holes when measuring, and my magnets do not stick to the sub.
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From: Santa Clarita CA
Drifting
Joined: Jan 2014
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From: Jefferson City Missouri
The engine cradle will bend to a certain point before cracking. If the frame rail was bent as bad as you said then the cradle bent too. It would be better to replace the cradle because once that aluminum bends like that it will crack and break if you make an attempt to straighten it. If it does not crack when you straighten it, the stress point will be so weak that eventually it will break and you could have a mess on your hands.
Race Director
Joined: Sep 2007
Posts: 16,557
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
The engine cradle will bend to a certain point before cracking. If the frame rail was bent as bad as you said then the cradle bent too. It would be better to replace the cradle because once that aluminum bends like that it will crack and break if you make an attempt to straighten it. If it does not crack when you straighten it, the stress point will be so weak that eventually it will break and you could have a mess on your hands.
There are many different alloys and methods of manufacturing aluminum products to be able to handle the intended purpose with the least chance of failure. Just a visual tells me the cradle is a casting and the design is such that it's engineered for stiffness. The alloy isn't so hard that cracking under stress would be easy, however once stretched, you can't shrink it back to it's original shape.I'd suggest finding another undamaged cradle to verify the mounting measurements will match your current frame attachment points, since it sounds like the frame was also stretched.
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