I am about to purchase a '77 or '78 Z. I've seen a few in person that had cracks along the roof rail just as the rail leave the roof along the hatchback. What causes this and should I be wary? Also, where is the C-Clip located? I know about the floor pan and frame rail rust issue. Are there other structural issues I need to keep in mind before my purchase?

Is the engine modded for enormous horsepower? Maybe a V8 conversion? Enough torque can cause the body to distort and fatigue.

Monster power can do that, but a stiff suspension combined with years of fatigue and or rust, can cause the paint to crack in that area. It is a factory body seam that can crack. Although it is often just paint or sub-filler crack. It is very common, and usually not a huge deal. It's not a fatal sign by any means. Look closely for rust elsewhere.

C-Clip? I only know of a handful of C-clips on a Z car. Shifter, throttle linkage, brake linkage, clutch linkage maybe, and a few other places, if that is what you are asking.

Again, RUST, RUST, RUST, and it can be hidden very well, so look deep. A little bit of rust, the size of a dime, on the lower portions of the car, is often the tip of a large iceberg.

My car had a crack on the drivers side when I purchased it. After carefully sanding it down (the seam is filled with a lead bead on early cars, not sure about later S30s) my body guy cleaned and filled the seam with body sealer during prep work. The crack is starting to re-appear. I just spent over 7 grand getting the car painted and would like to resolve this.

I do have a rear anti-sway bar. Could that contribute to the cracking during hard cornering?

Sorry about the hijack but although it may not be a big deal you should know that the crack may come back even after it is "fixed".

Common issue.Had them on two cars in the past,and neither had"monster power".

Common issue.Had them on two cars in the past,and neither had"monster power".

But can they be "cured"?

It sounds like what you are referring to is the body seam where the roof is connected. From the factory it was sealed with lead before painting. Normal body flex and vibration can cause the small cracks over time

C-clip? Did you mean c-pillar?

Can you just post pictures of it? visual aids are worth a thousand words.

my body guy cleaned and filled the seam with body sealer during prep work. The crack is starting to re-appear.

Body sealer does not a mechanical joint make.

If there is panel flex happening, that needs to be remedied before any cosmetic is applied.

A few tiny tack welds along the seam THEN a body filler.

If you have any recourse with your body man I'd take it up:mad:

Body-flexing is causing that joint covering compound to crack. That body flexing, as mentioned, can be due to excessive horsepower for the car, or spirited driving over uneven surfaces at speed.

However, it may also be due to another set of spot welds elsewhere in the car having given way and therefore allowing that part of the car to flex more than it should. It should be noted however, that this particular joint is a known problem site.

Additionally, repairs to other parts of the car, being done without proper support of the main body can cause this same situation. A complete rocker panel replacement, floor pan removal and re-installation, are but two that come to mind.

But, as Graeme points out, Seam Sealer, caulking, even Bondo or spot fiberglass are NOT a substitute for a proper mechanical joint. The lead cracked due to the flex in the joint, and lead is used both for it's hardness AND it's malleability (i.e. flex), but excessive flexing is what caused it to fail (whether due to range or cyclic flexing).

FWIW

E

Just thought I would add a few illustrations to further define the problem and support what has been said.

My personal take on this problem, would point to a body design problem that was bound to show up sooner or later, depending on the individual cars usage, as well as the combined effects of time induced metal fatigue and the very likely (in many cases), rust corrosion which weakens the lower unibody structure, thereby putting an increased amount of stress on the roof support and quarter panel seam. It is not stout enough to carry the weight or flexing forces exerted at this point after weakening of the lower shell has occurred. Steps must be taken to strengthen the shell in its entirety to relieve the destructive flexing at this joint.