I have now set up a system where I can spray rust remover liquid onto the rusty parts on the undercarriage permanently. I´m using a recirculating pump to spray on the rust remover which is then dripping onto a plastic cover. From there it will flow back into a large bucket where the pump is in and recirculates the fluid back onto the car.
I´m using a german product called "Rostio" - it's a concentrate used for de-rusting fuel tanks. You have to mix it with hot water. I have also heard great things about Evapo Rust.

I let my system run for days until all the surface rust was gone. The advantage is that the liquid can now get everywhere and should remove the last little piece of rust.
You will be surprised how well this works. This area now looks like a new car. There is not the slightest trace of rust to be found after 12 hours of spraying the car.
After spraying it with the rust remover you then have to flush it with water thoroughly and then dry it properly to avoid flash rust.

I also used various wire brushes and other abrasive materials to remove rust and strip bad paint.

I simply used a garden hose and shower to spray the rust remover on.
As you can see it only leaves rust free metal behind - I always let it run for 2 - 12 hours - depending on the amount of rust that had to be removed.
The liquid is collecting in the big bucket where I put the pump in to recirculate it.

You can spray the liquid everywhere
A "before" picture
You can also remove the rust from the brakes without disassembling them. A before picture
After cleaning - the brake cylinder developed flash rust immediately again.
As you can see - the rust is gone

The liquid also works great on brake drums - the original factory markings were still there.
Cleaned the fuel tank with the wire brush and painted it afterwards with tank paint from Eastwood

Cleaned the wheelhousings as well - stripped all the paint in there as well.
≈
Cleaned the fuel tank with the wire brush and painted it afterwards with tank paint from Eastwood

Tags:1974, 1974 Cadillac Coupe DeVille, 1974 Cadillac Repair Tip, Underbody, Undercarriage, Undercoating, Rust removal, Rust removal gel

This is my winter project for 2015/2016: Cleaning the undercarriage of the 74 to look like new again. The plan is to remove the surface rust, change the shocks, do some brake work like replacing the brake hoses as a safety measure, change the heater core, rebuild the AC, change all fluids, give the car a good tune up, and to change the lights to be street legal to get the car on the road next year.
Some other smaller things could happen as well…
The plan is to make the car to look and drive like new until next season. It's such a great car!
I think there are many different approaches for removing the rust from the bottom side of a car.

My personal method and plan so far, was to scrape any loose rust off with a wire brush.
I then steam cleaned the undercarriage.
Next step was to apply a rust removing gel, which I let on over night. Then I steam cleaned the car again to get rid of the gel. The gel is a quite a bit of pain to remove if it's getting dry, especially as I had to do the steam cleaning with the car on jack stands and limited access to the undercarriage. (I can't do this inside the garage over the pit)
So a lot of manual cleaning is necessary after the pressure wash to get rid of the gel on areas I cannot hit during the pressure wash... I then applied the gel once again and did the same routine all over again.

I will now mechanically remove the more stubborn rust with some pneumatic tools and wire brushes of various sizes I borrowed from my dear friend Richard.
Once the rust is completely removed, I will use the gel for a last time.
I will then use fine sandpaper to achieve a smooth surface of all metal parts.
If afterwards there is still some minor corrosion left I´m planning to use a rust converter and rust encapsulator to paint everything.
The oil pan and transmission oil pan will be painted in Bill Hirsch Cadillac blue again. I will completely clean up the fuel and brake lines as well.

The frame and chassis parts will most probably get painted with Eastwood Extreme Chassis Paint in satin black. As a last step I will cover everything in a transparent undercoating wax. This project will keep me busy until next spring as I want to do it very thoroughly and as perfectly as possible. The most common approach most people would do, is to knock off any loose rust, and then paint it with rust converter and rust encapsulator. Thats perfectly fine as well - but I want the underside of my car better than new and in perfect show quality like the rest of the car

You can find all the pictures of the “Restoration“ here.

The 74 has some light surface rust on the undercarriage as most areas were left bare metal at the factory. The original owner did not have the car undercoated. Its nothing major - it is more a cosmetic thing than anything else. I want the car to look as good on the underside as it looks from the in and outside. I will remove as much rust as possible with a wire brush and then use rust removal gel to get rid of all the rust. It´s a messy job - but I want to do it as thoroughly as possible. After everything is clean I will paint the frame with rust preventive paint in semi gloss black paint.
The pit in my garage - this is how I will see my car most of the time for the next months… You can see that I applied some rust removal gel to some areas already. I steam-cleaned the undercarriage before.

A small test spot after only one application of the gel - 2-3 more are recommended.

Thats the gel I´m using - it seems to be a great product. I got it through www.rostio.de .
After the first coat of rust remover gel. It looks very promising.

Tags:1974, 1974 Cadillac Coupe DeVille, 1974 Cadillac Repair Tip, Undercarriage, Rust removal, Rust removal gel, Rostio