Gator81

On the passenger side, there are two holes in the frame, one on top, one on bottom, right next to where the engine mount is welded on. These holes are ovals, maybe 7/8" by 1-1/4". They serve no purpose now, so I figure they are alignment holes used when the frame is being assembled. That's where my frame is cracked.

There are two cracks radiating out from that lower oval hole, going toward the engine mount. They run all the way from the edge of the hole, across the bottom of the frame rail, and then turn up the inside of the rail, under the engine mount, extending upwards perhaps a half-inch. That makes both cracks maybe 1-1/2 inches long. You know how these frames are made - they're like mirror-image C-shaped sections, placed together with a little overlap, and then welded to make a boxed rail. But the welding is not continuous - there will be 3 or 4 inches of welding, and then a 3 or 4 inch skip. Well, those two cracks are at the end of one of those welds. There is a space of 4 inches or so, rearward of those cracks, where the frame sections are not welded together. Then, at the beginning of the next weld, there is a third crack, about 1 inch long, in the same frame section and running in the same direction.

It is obvious that I'm getting some significant flexing of the frame there. I can't say how long those cracks have been there. I certainly didn't notice them when I was rebuilding the front suspension 2 years ago, and I was doing a lot of work right where the cracks are. I like to think that I am more observant than the average Joe, but who knows? My gut feeling is that there was some minor damage in this area years ago, before I had the car (I know that corner was hit and repaired), and that the extra stress of the much more rigid new suspension (springs, sway bars, tires) caused that minor damage to expand and become obvious.

Regardless of all that, I guess I've got to weld those cracks up. Does anyone here have any experience with this? I don't. I'm a pretty good stick welder, and I'm not afraid to tackle it. But perhaps it should be done with a MIG, by a pro at a shop that repairs frames. And what about pre-load? Should it be welded with the weight on the wheels, or not? If not, where should the weight be supported? How do I know that I've got the frame twist back into a neutral position before the welding occurs? Help!

Gator81

73 views and no responses? C'mon guys, somebody on here knows about this stuff! I've got to get this fixed, and I need to know what you know!

Twin_Turbo

You should weld a bar across the frame so it doesn't collapse and then cut out the affected section, weld a plate under it to reinforce the section and weld the original section back on, using plug weelds and beads running along the parting seams, cutting the sections off lets you repair the cracks and the extra metal reinforces the area...at least that's how I would do it.

The flexing is there on all c3s and can be a big problem, there are ways to help the frame in this area with gussetts. Before you start measure the frame dimensions and check if everything is still straight. Shouldn't be too hard a fix, just a lot of work. You will probably have to remove the engine to do it properly.

Stick welding will get the job done, in fact stick will have more penetration than a low amperage mig welder but a good mig welder (160 amps or so) with gas is preferred to get nice clean welds. You can reinforce it with the extra metal and grind off the outer surface for a clean stock look without compromising the strength, I would not just run beads on the cracks and grind it off, chances are it will crack again.

American Boy

We welded a crack on my 1980. What we did prior to welding was to jack the car since the crack went from the middle of the frame rail in height toward the floor. That closed the gap and then we welded it. Be sure to grind a V in the crack and weld 3 passes. One in the middle and one on each side for added strenght. You see it more but you're sure it won't crack again there.

Stephan

nostgry

Ok... I do frames. First , forget the stick weld stuff. Go to a frame shop or a Chevy dealer. Make sure they have a frame measureing system. Make sure they use a computer, some shops still just use tape measures. In particular a Genesis or a Shark measureing system. These use either laser or ultrasound to measure precisely the height, length and width of your frame. If you do have a twist or an area that's "short" due to an accident it will come up on the diagnostic check. It will show down to a single millimeter off. You then can resolve a price to correct any old damage and have the welding done too. Also make sure you get the pre-repair inspection sheet and the final inspection sheet from the repair shop. Don't hesitate to ask them questions either. The whole thing if they have to pull it shouldn't be more than $500.00.

Hey how bout that a Shark may just measure a Shark.

ckerch

I am up here in the flint area and have called many shops here to do the kind of frame checks you mentioned. Can you reccomend any shops around here or would you be interested in checking mine?

45ACP

Do you have access to the dimensions of C3 frames? For a number of years I have wanted that data to stash away for reference.

nostgry

Ok 2 answers. First CKerch - I'm not familiar with any shops up in Flint, but a Chevy dealer should have access to the program needed to measure your Corvette. If you're not satisfied with anyone in your area then I can check into getting the program from Chief. I may be able to help in the repair area if you run out of options.

Now 45ACP - I guess I'm gonna have to look into this further. I just checked my Corvette assembly manuel and they only give 2 frame dimensions. Those are only for the center "box" section. Very vague.
I'll check fellas PM me in a week.

MotorHead

For cracks that big you can mig weld them and they will be fine, try not to burn through. This is no big deal in my opinion and would take someone 1/2 hour at most including jacking up the car.