Tech Article: Lower Fender Rust on Early Zs
by Ben Pila
There are many areas on early Zs (1970-78) that eventually will rust. One of these areas is the lower section near the bottom of each fender. Usually you first notice a little paint bubbling below the emblem. As the bubbles continue to grow, the paint breaks and rust makes it's appearance. This is the common scenario with the early Zs that most of us who own them will see someday.
The rust on the lower fenders actually begins on the other side of the metal where it isn't seen from the outside. The rust problem is caused by two things. One is that the inside surface of the fenders (especially the rear/lower section,) are only painted with a light, reddish primer. This primer, in most cases is too thin and not able to thwart the long term effects of moisture clinging to it's surface. What keeps the moisture there is yet another Nissan engineering marvel. Some engineer back in the 60s thought is would be fine to allow the wiper cowl area to drain off it's water and leaves and debris right down into the bottom of the inside fender areas. The cowl I'm talking about is under the wiper grill. As water and such gets into this area, it has to drain out or it would flood inside the cabin. The Nissan engineers designed a rubber tube that attaches to the side of the fender well (just ahead of the door hinges,) which is about an inch or so in diameter and extends half way down. If you peek your head into the fender well, you would see this tube. Basically, when leaves and dirt accumulate at the fender bottoms, they form a sponge pack. This pack of debris holds moisture against the thinly primed metal and "Voila" rust. There is hope out there to remedy this situation, so don't despair, repair!
So you've removed your fenders and want to fix the rust. The actual rust fixing of the fender isn't that difficult if it hasn't gotten too big on the fender. If the rust is light, you can sand blast it off and either use fiberglass filler or fill it with a high quality aluminized filler (which is resistant to water.) If the rust is more extensive, then cutting out the "cancer" and welding in new metal is probably the best thing. Now, you've fixed the fender and you are ready to reinstall it. Wait! If you put the fender back on like it was before, the rust may come back again. What you need to do is to correct or remedy the engineering problem with the cowl drain tube. There are probably a number of ways to fix the tube right. I think in general, the outlet of the tube can't be allowed to dump anywhere near the bottom of the fender area. Perhaps lengthening it and redirecting the outlet to a different area would solve the problem. Also, apply a good top coating to the inside of the fender and wheel well areas before installing the fenders. There is something called Body Schutz which is sold by PPG through the paint and body suppliers. It can be sprayed onto the area leaving a hard and tough factory type of an undercoating in place. There are also many high quality coatings available from the Eastwood Company (215) 640-1450 (PA.) Call them and get their catalog of restoration supplies and tools. When you are done with the fender install, if you've gone the extra measure, you can rest assured that rust won't get that area again.