Undercarige Rust

[ladorn45]

Hey Everyone been reading up on things I can do to prep the under side of my car to prolong its life from rust. I was curious to what suggestion you guys might have to help ( products procedures). Thanks everyone in advance.

 

[Sub]

1. When driving over salted or brine covered roads, pressure rinse the undercarriage as soon as practical, every time.

2. Wherever rust appears, treat it with phosphoric acid. Let that sit for no less than 4 hours, but no more than one day. Neutralize the acid with baking soda dissolved in water, and be prepared to immediately coat with a protectant once dry.

3. Protectants: Different undercarriage components require different coatings, based on the function of the component.

A. Waxed Dipped Frame: The frame flexes, (especially the open G channel frame of the 2500... more so than the fully boxed but thinner frame of the 1500) so a flexible coating performs better in the long term on the frame. GM recommends NOX RUST X-121-B, a professional grade one coat rust preventative coating in a rattle can by Daubert Chemical Company. It is compatible with the existing coating applied by GM at the factory, and is recommended by GM following frame repairs after collisions.

Note: I personally don't use popular products that are target marketed to consumers with a lot of hype, such as Por 15 or Chassis Saver, but a lot of people do, and therefore those two products in particular should at least be mentioned here.

One product that I don't recommend is 3M Rubberized Undercoating. I have found that it is not as durable in the long term, especially in areas of elevated temperatures, such as near exhaust components. I also believe it is a water based product for consumer safety and/or regulatory compliance, and that may be a contributing factor in the lack of durability that I have found with that product.

B. NON-waxed dipped Painted Steel Chassis Components: Skid Plates, Transmission Crossmembers, Axle Tubes and Housings, Torsion Bars, Upper and Lower Control Arms, Shock Tubes and Towers, etc etc. The key product I use to prevent these items from rusting is FREE, and PLENTIFUL, and yet it gets thrown away by most people. Used automatic transmission fluid. ATF is loaded with corrosion inhibitors. Ever pull the pan down from an auto tranny? Notice how clean it is inside? If you service your Automatic transmission at the recommended intervals, then the fluid is still "good" enough for those anti corrosion inhibitors to continue to do their duty in protecting other chassis components under the vehicle.

I simply soak a rag with the stuff, and start wiping down every non waxed surface under the chassis that seems in appropriate need of protection. The ATF cleans the dirt off, and unlike motor oil or grease, the ATF doesn't smell, nor does it seem to attract as much dust and dirt after application. For this to be effective, it must be reapplied regularly, so it is a routine I incorporate into my oil changes.

 

[08grey]

Good info there^^^

If you want easy spray on products you can spray your undercarriage with fluid film before winter months and in the summer treat any already rusty areas and cover with a good 2k paint. Check under your spare tire to guage how much rust you really have.

 

[ladorn45]

Hey thanks for all the awesome info. I just want to make clear what the proccess is. So i was was going to get 80 grit sponge sand paper and just sand off as much rust as i can and then spray the spot with phosphoric acid after 4 hours spray with water baking soda then whip off with a towel and then was going to take the extra step and use a heat gun to make sure there is not water left. Fianly do i just spray on the NOX RUST X-121-B or do I have to use some type of primer. Also what brands and place do you get phosphoric acid, and is NOX RUST X-121-B my best option cause it seems there is only one place i can buy it and shipping is as much as the can lol. Sorry i know these might be dumb question but rather be the idiot that ask it then the idiot thats does not and does it all wrong.

 

[08grey]

I used por 15 and did it per their spec then top coated with uncoat and 3 years later it's still holding up well.

 

[jough]

For hot wax dipped frames, I use a motorcycle chain lubricant called Chain Wax to coat and seal any surface rust on the frame, under the body, bolts & nuts, etc. You can get it at most dirt bike shops.

 

[ladorn45]

I have thinking or por 15 or rustbullet. I know sub you mention that it might not be the best but i took a second look at my frame and pretty much all the NOX RUST X-121-B that gm put on is for the most part gone so i was thinking of going crazy and scrap the rest off and por 15 or rust bullet it and the even go the extra and spray NOX RUST X-121-B, over the por 15 anythoughts.

 

[08grey]

I have used por 15 for years now. It's a solid product.

 

[Sub]

I have thinking or por 15 or rustbullet. I know sub you mention that it might not be the best but i took a second look at my frame and pretty much all the NOX RUST X-121-B that gm put on is for the most part gone so i was thinking of going crazy and scrap the rest off and por 15 or rust bullet it and the even go the extra and spray NOX RUST X-121-B, over the por 15 anythoughts.

Just to be clear, GM does NOT install NOX RUST X-121-B at the factory. GM wax dipped the frames in our GMT800 era. Rather, GM recommended NOX RUST X-121-B to professional body and frame repair shops, as well as to upfitters who modify wheelbases to GM vehicles for vocational bodies, livery (limo), and motorhome applications. Once a factory frame is cut or spliced or welded upon, something needs to be done to it to protect it from corrosion. Since it is impractical to re-wax dip the frame after the fact of manufacture, GM identified a product in a rattle can that they deemed as an acceptable substitute, and that is compatible with the factory coating process.

---------- Post added at 05:46 PM ---------- Previous post was at 04:17 PM ----------

Here is an area of my chassis behind the rear wheel, traditionally one of the worst places on a vehicle chassis, as it is subjected to the sand and water blasting spray from all four tires that winds it's windswept way to the back of the vehicle before escaping into the departed atmosphere.

Granted, I live in a mild climate, where the roads are not salted. But I do drive through the snowy mountains from time to time. And, I have never garaged this vehicle, as I don't have a garage it would fit in.

But one thing I do is stay on top of even the slightest sign of rust developing. I may not wash the car in a year, but I will inspect under the chassis every month or two, and treat any corrosion cropping up immediately. I think that this photo encapsulates the essence of the recommendations I made in my earlier post. Ten years outside, and this is my chassis: