Crack in the Body

[palosfv3]

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.

[geezer]

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.

[JohnnyO]

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

[kenz240z]

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

[cygnusx1]

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.

[geezer]

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 January 5, 2011 by geezer
inserted disclaimer in first sentence