A bit concerned about chassis tubing

[Bill_VA]

Yesterday, the Capitol Area Cobra Club took a nice run through DC. A fellow CACC member was driving his FFR coupe and hit a curb at a relatively slow speed with his left-front tire. You would suspect that the LCA would bend or the mounting tabs would break/bend, but no. The 4" tubing ripped! Correct me if I'm wrong, but steel tubing probably shouldn't do this, should it?

https://lh4.googleusercontent.com/-nBeL6vK-Cgk/TwDd4vv5hMI/AAAAAAAAv8o/dh97SMVnzbk/s720/IMG_3287.JPG

[frankeeski]

Bill, Once heat is put to steel it does things. Depending on how the weld was allowed to cool the metal may have been compromised. I'm not a metallurgic expert but I have seen strange things like this happen to metal when welded. I'm not saying it should happen, only that it can. A call to FFR with pictures in an email are in order I think. I know it can be fixed relatively easily. Gussets over the open area with new tabs for the LCA should do the trick. It's a bummer that it happened though. Frank

[Ray]

Is that oxidation inside the tube?

Ray

[skullandbones]

I think that is great advice. FFR will be very interested from a quality perspective. I have seen some pretty extreme damage done to suspension when hitting a curb or other odd accidents where the forces (vectors) are much different than in normal design parameters. This could be a one off sort of thing that may not be seen, again. That would be my hope anyway. WEK.

[Richard Oben]

Looking at the pic I do not see a bushing but a rod end, that tells me this car has seen some serious track time. The heat affected zone from the weld appears to be work hardended by the suspension. I agree there is more to find out here than meets the eye. Jim or Jesper at FFR will take a Look I am sure.

The inside of all the tubes is bare steel, unless you coat it on your own it will get a coating of rust on it, just the condensation of the air will do that. Some have drilled holes in the front and rear to put a coating of some sort in the tubing. I do not see this dust of rust as a contributing factor. JMHO, YMMV, Richard.

[Mark Dougherty]

normally the lower control arm will fold up. There are a few things going on here though.
1)the lower arm has been modified to accept a Heim joint, and if you look closely you will see where the theaded end has been bung welded in the tube. by filling the tube with a solid plug greatly strengthened the arm.
2) also eliminating the bushings took all the give away. thus transferring the load through the metal joint directly to the chassis.
3) did you happen to see the 4" round tube bent around the 4" cross tube. this was a considerable hit. Ill bet when this chassis gets measured it will be out on both sides, and the x will have a kink in it just below the welded cross joint.
check everything well.
these types of things can happen when one thing is modified the next part down the line can fail.
Later
Mark D

[Wade Chamberlain]

Cut/pasted from my reply on the other forum....

Reality check :rolleyes:

Something not mentioned is this particular car sees more track miles than street miles....AND it's had some pretty decent off-track excursions in its life (lots of them).

Looks like rust to me in the break to the right in the picture. My bet....it was cracked for a long time.

I wasn't on the cruise this year so I can't comment on how hard he hit the curb. Looking at the pic of the wheel, I don't think he just bumped it.

[Jim Schenck]

The damage in the picture makes sense given the circumstances and is not something out of the ordinary for any car sliding into a curb even at a fairly low speed. Given the fact that there is no bushing on the lower arm to take some of the impact shock load, the metal tore instead of bending. There is not much information being presented here but just going off the picture that is what I see. Also looks like a relatively easy fix for a Fab shop with no parts needed just some extra gusseting around the repair.

The earlier coupe frames were .095 main rails but were changed to .125 to avoid confusion in manufacuring. (The coupe main rails are longer but the crossmembers are the same)