Over a period about two weeks, in between work and family, I restored the rear undercarriage of the Cutlass. The fuel tank had to be pulled to repair a pinhole leak, and I saw some exposed metal on the floor and trunk pans that we didn’t like. I figured, as long as the fuel tank is out, which took about 30 minutes to pull, I might as well spend 20 hours painting half of the car, right? Why do we always work on the parts of the car that no one will ever see? This is one of those projects that quickly snowballed out of control. It ended up taking about 20 hours and a lot of elbow grease.
Before Pictures
Here are the pictures of the fuel tank leak and removal that started the whole thing.
Here are the before pictures of the rear undercarriage body and frame, at various stages of cleaning, but before painting or wire brushing. Notice the evil dirt and rust that had to be exorcised.
Scope
Since I knew I wasn’t ready to do the whole car, choosing where to stop was fairly difficult. I decided to do from the front of the rear wheel wells all the way to the rear bumper brackets. I did not do the wheel wells themselves at the time, since they were well coated, and I haven’t decided my preferred approach for them yet. I left the brake lines and exhaust on the car and attached. The exhaust I would spray around, and remove any over spray that found it’s way to the pipes. For the brake lines, I didn’t mind if paint got on them to help protect them. I did not do the rear axle at this time, since I plan to replace it with a POSI unit and disc brakes.
Prep
Before doing anything else we needed access to all the relevant areas. We raised the rear of the car, removed the wheels, disconnected all four link arms to the axle, removed the fuel tank, removed the rear bumper and lights, removed the rear light wiring harness. All in all disassembly didn’t take too long since it’s fairly simple, but this is one of those times I really wish I had a lift. We lowered the rear axle to get more access to the frame above, and to remove the springs and shocks so we could get to those areas. In hindsight, we should have just completely pulled the rear axle from the car and restored it too, but we already had a large scope to deal with.
Once most areas were removed, we soap and water washed the whole rear half of the car, including spraying in all the hard to reach areas on the bottom. This was amazing. All of the nasty grease, sand, mud, water and soap obeyed the laws of gravity nicely and ran off of the car directly onto my face and body just like I wanted. Seriously, if you can find a lift you should pay any price to use it for this. The scrubbing took a great deal of time, approximately 6 hours to get into all the hard to reach areas. This was a lot of work, probably the worst part of the whole project. Frame-off certainly would have helped.
After tons of scrubbing, we scraped any loose old coatings off of the body.
After scrubbing, I decided to wirebrush the entire area to be painted. This was EXTREMELY dirty. Wow. I basically used a couple hand brushes, as well as a wire wheel attached to my power drill. This got the bulk of any loose coatings and surface rust off of the frame and body. The dust was incredible, and it left metal, wire, and dirt everywhere. Make sure you wear a face mask, gloves and safety glasses for this part. Even with a face mask I was coughing dust for a couple days. Turn on a fan for good ventilation.
Here is where I probably made a mistake. After wire brushing, I decided to use phosphoric acid rust converter to treat any remaining rusty areas. I left the acid to work overnight per the directions. The rust converter did a good job on the rust, however the acid dried overnight and left phosphate precipitate all over the place, also known as the “dreaded white residue”. This residue is not paintable, and had to be removed, although there really is no good way to do it except to wirebrush the entire area again. Soap and water didn’t have much impact. So I ended up scrubbing the entire car underside again, AND then wire brushing the entire underside again. this was terrible. If you’re reading this, just skip the rust converter step unless you’re doing a couple isolated areas. Rather wirebrush the area until you get to good metal. It will be easier in the long run.
Here are the pictures after cleaning and wirebrushing, with the rust converter applied. Compared to the before pictures the rust was significantly converted/reduced. Look at the pictures of the bumper bracket for a direct comparison to before and after.
Paint
Finally it’s time to paint! Paint and primer choice is up to you’re personal preferences, but make sure your primer is compatible with your paint. What I would recommend staying away from is “undercarriage” coating. This stuff is terrible. It was actually applied to my car by a previous owner, and most of it fell off requiring all of the work above. Truck bed liner is not the same as undercarriage coating, and is a very good product. But, it doesn’t have a smooth surface, if that’s what you’re after. It will also tend to look dirty. I opted for good old fashion paint and primer. Regardless of what you choose, it will be better than exposed rust or metal that was there.
After ensuring everything was clean, we used primer on all areas to be painted. We made sure the primer we used was a different color than the paint so any missed areas would be apparent. The primer laid down well and the type we used could be re-coated after 15 minutes. Since the car was largely assembled, I used pieces of carboard as paint shields to avoid overspray, and obviously masking taped anything necessary.
Here are the pictures with primer applied.
15 minutes after primer, the paint went on. Semi-gloss black was my choice for the body and frame. I made sure to hit any nooks and crannies really well. After 15 minutes a second, and the again a third coat was applied. Including the primer, 4 coats of paint are on the car now and it should last a good long while.
After painting, we used some paint thinner to remove and overspray from the exhaust pipes or other areas.
Here are the final results at various stages of re-assembly!
Finished Job!
Obviously a frame off restoration is the preferred approach. However the project turned out very well and the car is certainly better off for it. While we were in there we replaced the rubber fuel lines, and did some light socket repair since the bumper and tank were off. Thanks for reading!
I’ve since decided to clean and restore the original rear axle as well. That write-up can be seen HERE!
LEFTLANEBRAIN
