Tech Article: Bubbling Paint/Rust Syndrome
by Ben Pila
On the early Zs circa 1970-78, a common thing happens to all on the wiper valances. This part is also called a wiper cowl and probably some other names too. This part is the sheetmetal body part that is between the back of the hood and the base of the windshield. It covers the wiper arm linkage, wiper motor and the trough where water drains from the cowl vent. The vents cut out into the grill help with the ventilation in the cabin of the Z.
Now what happens to almost all of these valances is they rust on both sides (visible on the large surface area on each side.) The rust is exactly in the same location on every Z, 1978 and older. The 1979-83 ZXs have a rust problem in their cowls too but I'll talk about that some other time. What causes the rust is simply the fact that Nissan in the 70s didn't feel these cars would be around as long as they have been and consequently didn't put much in the way of rust proofing under or inside of the inner sheetmetal. If you were to remove the wiper valance, you'd find a red primered surface which is not very good at keeping moisture away from the metal under it. Either attached to the valance (most of the time,) or to the metal frame/support under the valance, you'll find a white foam pad about the size of a letter envelope and a little over 1/8" thick. This pad served the purpose of cushioning the ends of the flat areas of the valance. Unfortunately, Nissan again used the wrong materials with this pad. This pad is an open cell material which like a sponge and absorbs water while holding it against the thinly primered sheetmetal. The result is seen as a little bubbling under the paint that eventually breaks through the paint and continues to grow into holes.
How do you fix this rust or potential rust problem? If you have a clean looking wiper valance, you should remove it and remove the white foam pads. Replace the pads with a closed cell foam like a wet suit material or other suitable material and reglue with weatherstrip cement to the valance. If the primer surface is ok, then sand and paint the under side with a good paint to seal the underside from moisture attack. If your valance is bubbling like mine is, then you'll have to remove it and sand blast both sides to remove the rust. Filling the underside rust holes can be done with fiberglass and use a good body filler on the top surface. If the rust holes are large, you can either weld in new metal or replace the valance with another one. What you are trying to do is to fix the problem and make sure it doesn't happen again. To remove the valance, remove both wiper arms and the sheetmetal screws directly in front of the cowl and simply lift it out. Make sure not to loose the black plastic inserts at the windshield side. Replace these inserts if they are broken or missing. One other thing to do while you have the cowl off is to glue a sheet of window screen material under the vent slots. This will keep the tree and plant droppings from getting into the cowl and potentially plugging up the drains. Use a clear silicone adhesive to glue the fiberglass or aluminum screen material.
If you can catch the rust at the early stages, you can save the valance and any other parts on your Z too. Unfortunately again, the early Zs had very little rust protection so other areas rust the same. I'll detail which other areas have problems in future articles and how to repair them. With Summer coming and nicer weather, it's the best time to do the bodywork/restoration on your Z. Remember, "Rust never sleeps!"