The Stovebolt Site Forums The Shop Area General Truck Talk Undercoating

Did the original trucks have any undercoating in the fender wells or were they just painted?

Thanks

I can't tell on mine. The underside of the fenders were coated with road tar thrown off by the tires because is was a road construction truck. The underside of the cab, however did have some undercoating on it.

My understanding is no GM vehicle came from the factory with undercoat. It was a product sold and installed by the dealer as an add-on. Most did more harm than good because the person applying it would usually spray over and plug the drain holes causing more rust since any water couldn't drain away.

Interesting. So where are the drain holes?

My 54 has some thick tar like undercoat but only on the rocker panel area under the doors .I don’t know about the newer trucks but I don’t think undercoating would plug the drain holes on the A D trucks the holes are almost the size of a nickel.

More accurately I should have said drain openings. They sometimes were "holes" but often small arches along the bottom of the door skins where they meet the inner door, where inner fenders meet outer, etc.. There's no one map because every manufacturer had their own way of doing it. If we were together with your truck on a lift I could point some out to you. Anywhere rain water could get inside structure there were likely drain openings to let the water out. Most I've seen were much smaller than Kevinski mentioned. They don't need to be large to let water out so most I've seen weren't. That made them easier for the thick undercoat to plug.

Ok thanks for the explanation. So what is the general consensus on undercoating? I'm working on a '65 Chevy fleetside longbed and am planning to use rubberized undercoating on the bottom of the cab and fender wells.

I never had luck with that type of undercoating as it will also hold in the moisture and salt spray if it gets under it .In my area I use fluid film ,but if you don’t drive it in the winter or have salt spray that gets under the truck you may not need it.

In my experience the best undercoating is what was used in the 60s and it seemed to be the same thing they used to patch cracks in tarred roads and it was also used on flat roofs with gravel. It was nasty as anything, smelled terrible and had to be applied hot. There are three things I've found today that aren't bad. One is a water based paint sold under the name XO Rust. It is black, kind of flexible when dry and thick. It is also real hard to find now and it is expensive even if you find it in a hardware store that happens to stock it. https://www.amazon.com/True-Value-XO18-HP-Interior-Exterior/dp/B000C026CS That's what it looks like. I use that stuff in doors. Pour it in and turn the door one way and the other until all interior seams (where the skin and inner panel meet) are filled and the door is overall coated inside, too. Then let it dry really well and the door will be much less prone to rust even after a decade or so. Clean it as well as possible first and let it sit in the hot sun to dry for a couple of days before doing this. The other thing is a spray-on undercoating made by Permatex. It is the best of all the over the counter shake and spray products, but all of those have limitations. And the third thing is black plasti-dip. Thin it with naphtha about 1/3 naphtha to 2/3 plasti-dip and paint it on with an inexpensive chip brush. Wear old clothes because you'll get the stuff all over you. You can make it as thick as you want by adding coats, it is just like rubber once it dries and will deaden sound really well. But...it is very expensive. Good luck. Doing this today (just like in 1965) is hard work if you do it right. You have to start as clean and dry as possible and you can't just undercoat parts of things...coat everything you can get to. Water, salt, nothing will get through plasti-dip.

Unless you're working with a brand new vehicle fresh off the car hauler, the first thing to do is steam clean or pressure wash everywhere you intend to coat. otherwise, the undercoat simply traps dirt, road debris, and salt against the under body where it can do the most damage.
Jerry

Thanks guys appreciate the good advice

My 2 trucks 49 and 51 3100 have running boards which i painted top and bottom with bed liner. If you were to sand/wire brush the frame, the fenders you could paint/spray with bed liner to protect from rust FWIW Bill

Is bed liner better than something like 3M rubberized undercoating?

Definitely. The stuff is pretty durable. The same as any paint or undercoating, what you put it on has to be CLEAN, and scuffed so the product sticks.

Like 49 3100, my plan is to use spray-on bedliner for the running boards. They will be blasted and primered with epoxy first. Also considering it for the underside of the fenders to protect from rock chips.

In thinking more about the undercoating, I would like to see what you think about:

1. If the truck originally came from the factory without it, do I really want to do it?

2. It seems that the textured finish of bedliner or rubberized undercoating would tend to hold mud and dirt, whereas a slick surface not so much.

Thanks for your opinions

....my .02
On both my 37 (22 years ago) and my 52 panel, after blasting the chassis I painted with gloss black. I'm not a purist and no one see's it. I don't drive them on dirt roads, at least not very often, and its amazing how slick and clean they are when i slide under them. (and I drive them....drove the panel to homecoming and K.C.) the 37 has been a little of everywhere.
Even when working on them I can take a rag and it wipes off nice and clean.
....like i said, just my .02.

Thanks Achipmunk that is kind of how I'm thinking

The 2-part urethane bedliner can be applied textured or smooth. The shop I talked with said it was a matter of air pressure adjustment on the spray gun. When I had one of my fiberglass running boards on my F250 repaired and new bedliner applied, they did the top textured and the underside of the front end smooth where it gets peppered with gravel.

My panel truck has a generous layer of undercoat, presumably installed by the dealer when new. Every place there is undercoat, the underlying components are like new.

10-4 appreciate your input guys