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tickhead

Crack in the Body

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    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?

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

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    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.

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    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".

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

    But can they be "cured"?

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    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

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    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:

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    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

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    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.

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    Body flexing is not the only cause of lead seams cracking and in the case of Zs there will be other evidence of fatigue cracking in the body structure. The most common cause of failure in a leaded seam is improper cleaning of the flux residue after the metal is tinned. This is a critical step that must be diligently done before the seam is finish filled with lead. If not removed the acid residue will eventually eat through both metal and lead . All it needs is moisture and even the morning dew is enough to make it active.

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    Body flexing is not the only cause of lead seams cracking and in the case of Zs there will be other evidence of fatigue cracking in the body structure. The most common cause of failure in a leaded seam is improper cleaning of the flux residue after the metal is tinned. This is a critical step that must be diligently done before the seam is finish filled with lead. If not removed the acid residue will eventually eat through both metal and lead . All it needs is moisture and even the morning dew is enough to make it active.

    ^^Excellent points to consider.

    Taking a look at JohnnyO's particular problem, it reocurred after his bodyman redid the seam with filler. This is a recent paintjob and a darned shame this happened. I would heed Nissanman's advise and bring it back and ask them to repair it. I just hope a few well placed welds will correct it and they blend in the paint repair so it is unnoticeable.

    Just as an aside to the amount of flex in these old Z bodies. Try raising the front end of your Z while both doors are open and then carefully try closing the doors, checking for door drop. Some of them don't fair too well, including mine when I first bought it. That was one of the reasons why, when I replaced the floors and outer rockers, I also made up some full length floor supports to tie into the rear frame section, in an attempt to beef it up and add some more rigidity. But, a guy trying to achieve an original restoration might not want to go to these extremes.

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    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:

    I have not talked to my bodyman since he finished the job. I questioned him about is work habits and withheld payment until the job was completed so at this point the relationship is over. I do have enough paint left from the job to get an exact match and I think that is an easy enough area to feather in so I think I will take it to another shop and have them strip it and take a look at his so called fix. He was supposed to tack weld it first then fill it.

    E & Ron, I stripped the car to bare metal top and bottom, only had a few pin holes of rust on the drivers dogleg which I had removed and replaced and inspected the entire undercarraige for previous damage and repairs. The only repairs needed were the replacement of the floor pan rails that were pushed up slightly by a dummy with a jack.

    I guess the last 40 years of spirited driving may have weakened the frame somewhat but I don't know how 300 miles of driving only slightly spirited driving could have caused this to recur if it were repaired properly. cygnusx1 suggested that stiff suspension could have contributed to the crack but why not on the other side too? I do have a rear anti-sway bar but have not replaced my rear struts yet. I plan on using KYBs with the stock springs.

    I do not plan on putting in full length rails so I will have to take a good look at it with the new body guy. I will have him clean it all the way out and inspect it thoroughly and come up with a plan for a permanent fix.

    Thanks for all the input.

    John

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    Just a thought, could putting the car up on a lift or jack stands contribute to cracking at this seam?

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    One side cracking before the other is just happenstance. 300 miles after the bodywork? This has got to be poor workmanship.

    Stiff suspension places higher loads on the unibody, and more often. It would simply accelerate the cracking. My 280Z has begun to crack again, after 11 years, and with about 70k miles on the bodywork. I don't know how the seam was handled when the paint was redone. The chassis has about 180k miles on it now. I run a pretty tight street suspension, heavy sway bars, and no other chassis stiffening besides strut tower bars. The car is relatively rust free but has had its lower frame rails replaced at the 70k mile mark.

    How about you totally stock Z cars with high miles? Any roof cracking NOT related to rust on the car.

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    Just a thought, could putting the car up on a lift or jack stands contribute to cracking at this seam?

    I could be mistaken but from what I've seen, this joint was finished using the same processes, with the same underlying structure for all models of the early Zs. It is a matter of how each of these cars held up over the years, that will determine how intact the seam remains.

    The image I have flash through my mind is a Z travelling at a speed sufficient enough to cause a substantial downward force when a dip is encountered in the road. The combined weight of the occupants as well will increase the stress put on the unibody. There are countless factors that will make each car unique as well over its history. I noticed a post recently where someone was puzzled about his car being rusted much more on the LH (driver's) side. Living in the rustbelt, I instantly recognized this as a car that has been parked on the street and subjected to traffic splash/spray. Putting a car up on a lift or on jackstands, seems to me, to be more of a controlled, slow movement, but who knows, its possibly a contributing cause. I think potholes, speedbumps, railroad tracks and general rough, uneven surfaces are larger factors.

    In conclusion, I think a few well placed welds before re-leading or filling, prior to a paint job sure can't hurt.

    Edited by geezer
    inserted disclaimer in first sentence

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