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Hey guys I have a few questions about the '74 project I recently picked up. My main concern is a broken control arm mount on the driver side. It looks like someone poorly attempted to repair it at some point before. What is the best way to make sure everything is in the proper place before welding the repair and I was going to add some gussets to prevent any future damage.
 

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Hey guys I have a few questions about the '74 project I recently picked up. My main concern is a broken control arm mount on the driver side. It looks like someone poorly attempted to repair it at some point before. What is the best way to make sure everything is in the proper place before welding the repair and I was going to add some gussets to prevent any future damage.

Its unusual damage for a Corvette.


Usually just see those problems on severe abused drag race cars.



Kinda looks like the frame is thin from rust corrosion.
Most would say to replace the frame with a used frame.


It can be repaired yet but the only safe way is to make a custom plate about 4-5 times larger than or diameter surface area that broke away.
Entire area should be blasted clean with brand new virgin glass beads.
Then wire brushed again or use a Flap wheel in a disc angular grinder.
Mirror image exact as the undamged side cross checking over and over at least 5 times.
Clamp it.
Use a TIG Welder for maximum strength.

Tack weld.
Check again at least 3 times.
Weld in full and lay down perfect weld beads.
Just like Race car chassis work.
Only perfection done.
 

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I know it's allot more work but considering the metal looks a little thin in the upper left corner might it be safer to cut out and replace the front cross member.
 

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That frame is garbage. And likely if you were to inspect the body mounts and pillars you would find the bird cage is rotten as well. Here's hoping you didn't just buy this nightmare.

WHY do I call this a nightmare? Well because if you look at the picture of the passenger side you will see 4 bolts that go through the cross member that look like they are to support the same piece that broke off the driver side?

From the time you see this you need to inspect the rest of the frame as best you can for other stress cracks. These frames are NOTORIOUS for stress cracks. They love to crack around both front spring pockets. They like to crack where the frame support is on the driver side for the steering ram. They like to crack right where the frame starts to turn up to go over the rear axle. You need to spend time making an assessment on the rest of the frame. For your own safety.
 

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Discussion Starter #11
Thanks for the input guys, either way it looks like I've got my work cut out for me. I'm really considering maniacmechanics method as this was my original plan almost exactly but someone local is parting out a c3 and I'm considering calling them and seeing how much they would sell their complete cross member for or maybe the whole frame.
 

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Thanks for the input guys, either way it looks like I've got my work cut out for me. I'm really considering maniacmechanics method as this was my original plan almost exactly but someone local is parting out a c3 and I'm considering calling them and seeing how much they would sell their complete cross member for or maybe the whole frame.
You can not change that crossmember. If you try to remove it the engine will separate the 2 frame rails as there will be no support. Furthermore even if you remove the engine and trans and even the body, if you cut out the front crossmember, the car will never track straight or have a pair of tires last on it for any meaningful time again. This is especially true if you are attempting this without a plethora of experience in suspension work already under your belt. Fix the perch if you like, But don't destroy the frame by chopping the crossmember out. Please don't turn a problem into an abortion. butt weld the perch back in place, and then make some plates and weld the plates over the butt welds. So it has strength at the welds where you got the metal super hot and brittle from the welding. And don't forget to pray.
 

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This..




WWhiskey TTango FFoxtrot?!?!
I am actually pretty sure that these 4 bolts are to mount the perch that holds the front transverse composite spring that some think it is cool to convert to. So let me bestow some more wisdom on all of you here. The frame was designed and intended to be loaded at a certain place. This is the spring pockets. This is the strongest areas, by design, to the front half of the frame. Where the holes were drilled and the new front spring perches mounted is a little ways away from the designed and intended point of load by the manufacturer of that frame. And i think that ultimately this is why more people don't convert their c2 or c3 to the transverse composite spring up front. This likely could have been what broke your perch if you were still running this spring up front. And drilling all those holes in the front crossmember for all them bolts doesn't exactly help matters. But that is just my opinion and my 2 cents worth.
 

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I agree with Wiz, there are many C3's out there with this problem. It's a stress point and poor metal thickness. I won't go into detail here but if you go to my build thread you can see how I made the repair to this section on my frame with the same problem you are having. Also there is no way to fix this properly without removing the engine and several other things in the way. https://www.digitalcorvettes.com/forums/showthread.php?t=148376
 
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