This crack is in the rear conversion pan between the truck and the floor pans. The crack, as you will see, is right on the passenger side shock access opening. Ever see this? Anything else i should be concerned about???

[IMG]local://upfiles/48675/16C7987FE467446FB8B9555F3A6EAF7B.jpg[/IMG]

[IMG]local://upfiles/48675/5A180352417045AF8A57CBB398B804F7.jpg[/IMG]

 

That seems like an odd place for a crack to me but it should be an easy fix. For starters, drill an 1/8" or so small hole at the end of the crack to keep it from spreading further. Clean it up well with a flapwheel and weld it up.

 

+1 on the drilling of the hole at the end of the crack to check its advance. On the fastback, I had them develop below the rear window on the passenger side. Sucks, but there it is.

 

It looks like those cracks are in the area where the rear shocks mount and there is a might more rust inside that void than on the outside. In any case, it looks serious.
Jim

 

I have the same crack in the same spot on my Mach1.

I'm going to weld it up. Not to worried because its the top layer of metal and not the metal holding the shock.

 

Looking closer at the first pic, it looks like you may have the beginning of a second crack as well. Jim may be correct and there are other issues present. In your investigation, make certain that you do not have shocks that are too long. If they are limiting your downtravel, you're going to have problems.

 

I appreciate the tip. The car has been in storage for 27 years and it was not kind to it. There are two cracks around that opening. There is the large one and the smaller one on the other side. Here is an additional piece of information... The frame rail on that side is rotten. It has not come through the floor, but anymore driving and it might have. So, there is obviously additional stress on that side of the car. I also think there is a possibility of an crash point on the front apron, but the car is square (we verified this first...)

I also inspected inside the shock openings and underneath the car and those are some of the best parts on the car. They are solid and on the inside where the crack is, is still painted body color with no rust on it..

So, who knows. I am getting ready to pull the floors out so more inspection can be done at that point. The car is rusty, but salvagable. I am starting to wonder if some of the "on and off" of the flatbeds may not have caused some stress fractures... Who knows.

Any additional feedback would be awesome!!

 

get the car straight and level check in a shop manual for the messurements on the frame rails make sure they are straight then go to town on it.i looked at your other pictures before it does have alot of rust but anything can be fixed.just dont do like alot of people start a project to big for you or quit caring about it and end up selling it for less then you have in it.dont forget its a unibody car brace it up before cuting anything off it.

 

Hard use and/or abuse may have been responsible. Wheelstanding, hard launches or hard cornering, and hitting one-wheel bumps all put the chassis in torsion (which is a much tougher sort of load to design for than ordinary bending of the chassis due to the weight of a full passenger and/or trunk load). These loads don't have to be severe enough to start a crack right away from a single occurrence; fatigue damage is cumulative, and a crack is evidence onlythat the fatigue limit has been exceeded at that specific location.

Fastbacks have generally been more flexible and weakerin torsion than their sedan counterparts because you don't get as much help from the roof in those cars. The result is that while the loads are about the same (sedan vs fastback), the distribution of loads through the chassis structure is different, with the fastback being more highly stressed in some places. The lack of either a rear bulkhead or even diagonal bracing across the opening behind the rear seat in the fastback means that stresses would be higher in that general area as a result.

I'd also look carefully for any evidence that the cracks started at a notch or other discontinuity left in the metal by some forming operation during assembly or even from careless loading by a previous owner. Fatigue failures will almost always start at a "notch" or other sudden change in material shape/thickness ifsuch is present.

Norm

 

Andrew, thanks for that. We have already verified all the measurements. We had her on a frame rack before bringing it back here. She lines up just fine. You are correct. She is rusty, but nothing overwhelming. Like i have said before, with a rusty one, you dont feel so bad about modifying it.

NORM!!!! As far as what you are saying, i can see that. With the stresses being distributed differently in a fastback, i would assume to see more stress cracks. Interesting point.Now that you mentioned it, i kinda feel stupid for notthinking about it before!!!

Thanks!!