Last fall (2021) the undercarriage project of my 1966 Cadillac Coupe deVille started. The car is in fantastic condition. The factory or dealer applied rubberised undercoating was still on the car, but on some areas it was dry and brittle. In areas where it was not applied there was some slight surface rust which I also completely removed.

VIDEO RECAP

I did not plan to do a video about the restoration, but here is a short collage of some footage I had: (on youtube you can watch it in 4k HDR

This is a short video showing what was done.

BEFORE

Some "BEFORE" pictures showing how the car looked before I started working on it.

A picture showing the entire undercarriage


The undercoating in the wheelhousings was getting dry and brittle. Some rust formed underneath it on some areas.
Even the rubber splash aprons were covered in undercoating!The before pictures - great condition for an original car

The goal of this project was to freshen up the underbody and to conserve the condition of the car.

DRY ICE CLEANING - REMOVING UNDERCOATING

The biggest challenge was to remove the old undercoating by dry ice blasting. While in some areas it came off easily, there were some areas where it just would not come off at all, no matter how much dry ice was used and how much pressure we applied. This was the first time old undercoating could not completely be removed by dry ice cleaning - never had this problem on my 74 and the Roadmaster underbody projects before.
Thats why I decided to leave some of the original undercoating on the car. This would preserve the original look, and the new undercoating I used was perfect for working over old undercoating anyway.

The front wheelhousing after dry ice cleaning

The rear wheel housing after dry ice cleaning. Notice the factory overspray!

RUST REMOVAL

Next step was removing the surface rust which was everywhere. The car, coming out of California, did not have a rust problem at all, but the factory just left some areas unprotected where surface rust could develop. Getting the rust out of all the nooks and crannies is another challenge if you do not plan to disassemble the car completely.
I'm a fan of chemically removing rust as it gives more thorough results. Sandblasting is no good idea on an assembled car and is too abrasive.
On my 74 I came up with the idea of spraying the entire underbody with rust removing liquid for a longer period of time.
I set up a system where I could spray rust remover liquid onto the rusty parts on the undercarriage permanently. I used a recirculating pump to spray on the rust remover which is then dripping onto a plastic tarp. From there it flowed back into a large bucket where the pump was and recirculated the fluid back onto the car.
I used 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.

The rear axle area after rust removal.During rust removal - I sprayed on rust removing liquid for many hours.

I let my system run for days until all the surface rust was gone. The advantage is that the liquid could get everywhere and removed the last little pieces of rust.
You will be surprised how well this works. There were only minor traces of rust to be found after 24 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.

PAINTING

After rust removal I started masking and taping off all the areas which should not be painted like transmission, lines, cables, exhaust, screws and bolts and more. This took forever to do. Painting the undercarriage was next. Some hard to reach areas where painted with rust preventive paint first. Afterwards I used "Timemax Color" (its from a company which won every comparison test done by a classic car magazine). The first coat I sprayed on was grey, followed by 2 black coats. This way I could make sure that I did not miss any spots.
After a couple of days of curing time I sprayed two coats of transparent undercoating followed by a transparent 2k stone chip guard. This product is normally used for rally cars and is impossible to destroy and basically invisible.

The Timemax products I used. I have used them before on my 74 Cadillac and my Buick Roadmaster with great results.

Masking everything was a lot of work…
In the rear wheel housings I only used transparent material, because when the factory painted the car there was a lot of overspray in the rear wheelhousings which were an integral part of the body. I wanted the overspray to be visible.
When everything was painted the drive shaft looked out of place and the tank did not look as fresh as well. I took the shaft off the car and painted it replicating the color coded factory markers which could still be found on the shaft. I cleaned the tank and also painted it.

I repainted the tank with Eastwoods fuel tank paint.
The removed drive shaft before rust removal
Remains of the factory markings on the drive shaft
The fender skirts also needed a lot of cleaning on the inside. I removed the old undercoating with a lot of scrubbing with tar remover. Afterwards I applied transparent undercoating showing off the original surface of the skirts.
The fenderskirts were full of old undercoating as well.

The fender skirts before and after cleaning

SPLASH GUARDS

Reproduction splash guards are available from a couple of vendors. They are made of masticated rubber like the originals. They look great at first sight. When I wanted to install them instead of my dirty old ones I noticed that one hole was too small to install the original mounting screw and washer. When I compared the original splash guards to the reproductions, I noticed that there are many small differences to the original ones. I could have installed the reproductions with some modifications but I decided to reuse my originals instead. They were full of old undercoating as well and it took a lot of work to get them look like new again. It involved a lot of scrubbing and a pressure washer. The chrome trim of the front wheel housings had a lot of undercoating overspray as well which I had to get rid off as well. Tar remover slowly dissolved the overspray.

The rubber splash guards before
After cleaning
Some of the differences between the original and reproduction splash guards

I´m glad that this project is finished and the car now looks great from the underside as well ;-) It should be well protected even for the harshest conditions, but it probably wont ever get wet again anyway.

While I was down there I also replaced all 4 still original shocks and the front stabiliser linkage.

New and old front suspension parts

The front bumper buckets were slightly rusted as they were not protected in any way from the elements. On many cars these are rusted through. I chemically removed the rust and sealed them from the inside.

The outer front bumper buckets were rusted and I used rust removing gel to remove all the rust.

AFTER
Here is how the finished car looks.

Tags:1966 Cadillac Coupe deVille, 1966 Cadillac Repair Tips, 1966, Restoration, Underbody, Undercarriage, Undercoating Removal, Undercoating